Since I'm starting from scratch, I'm creating my final thread on this chassis/TV. I know multiple threads are frowned upon and that's why this one. It will serve as an update and help request in a single thread.

Okay, so I am tired of chasing issues, so I'm going to tackle the entire set, piece by piece. I'll start with the chassis and replace all electrolytics. I did that 13 years ago, but I know a little more about replacements than I did back then. I have ordered, where available, the exact replacement noted in the SM (Vishay and Cornell). I will also be testing, as best as can be while in circuit, all resistors and diodes.

My first task is to measure B+ and scope it. I will start at the test point and from there, test and scope at all the in and out points on each module. From the schematics I see that from the regulator it goes in this order: Chroma-->Subcarrier-->Video Processor-->Vertical-->Horizontal-->125V source for a complete loop. I want to do this before and after recapping and other diags to see if there is any noticeable change. I figure if it starts out clean, then gets noisier, I can pinpoint the issue better.

After the main stuff, I'll be replacing pots on the convergence board with NOS, replace IC on sound board in hopes of getting tone control back and fixing the channel motor as it gets stuck pretty often and requires a change up and down to get it to fully change channel. Once that is done, I'll do all adjustments per SM.

So that's my plan. Parts will be here Thursday, so I have plenty of time to measure and scope. I know I'll be here often to ask questions and request help, that's for sure. I've learned quite a bit from everyone here, so I think this will go well.

Now for my first questions. If the B+ is 125V, does that need to be dead on, or is there a +/- that's acceptable? The filtering comes from the multi-cap canister that I bypassed already, wanting the keep the canister for aesthetics. I wasn't able to find 400uf 150V, so I used 390uf 160V. I'm pretty sure that falls within the 20%. See attached pic.

Do the RGB output transistors have affect on image and such? The reason I ask is it originally came with 121-743 TO-5 package, but to replace one cost more than buying all three 121-868 TO-220 package. While this works, I miss the original look of the heatsinks with the plastic cage. As it stands now, they are just plugged in with a small clip-on heatsink on each. Looks crappy. If they do the exact same job, I'm going back as I got my hands on an NOS TO-5.

Well what do you know. I have another question.

I am searching for the 3 pots I don't have for the convergence board, but Zenith parts aren't out there. I started looking under the other part numbers. I managed to find all I need, but I'm not sure if they'll really do the job. The resistance numbers are off. For instance, the 300 ohm factory's replacement is 500 ohm, 60 ohm replacement is 50 ohm, 120 ohm replacement is 100 ohm and so on.

I can see how the 500 ohm works as it goes beyond the 300, but the others don't even reach the original. Zenith did put them down as replacements, so they must work, right?

My first task is to measure B+ and scope it. I will start at the test point and from there, test and scope at all the in and out points on each module. From the schematics I see that from the regulator it goes in this order: Chroma-->Subcarrier-->Video Processor-->Vertical-->Horizontal-->125V source for a complete loop. I want to do this before and after recapping and other diags to see if there is any noticeable change. I figure if it starts out clean, then gets noisier, I can pinpoint the issue better.


I just want to make sure you know not to scope the B+ unless your set is plugged into an isolation transformer, or you're using an entirely battery powered scope. You cannot scope anything in the set without isolating it or using a battery powered scope because the neutral line will short out to the ground lead on your scope probe because the neutral and the earth are connected at the circuit breaker.

I would, in general, recommend that an isolation transformer always be used for doing any live testing on a set, no matter how safe you think you're being, but I know not all people will do that.

Sorry if this is unneeded advice, but I just wanted to make sure that at least someone said this to you.

I just want to make sure you know not to scope the B+ unless your set is plugged into an isolation transformer, or you're using an entirely battery powered scope. You cannot scope anything in the set without isolating it or using a battery powered scope because the neutral line will short out to the ground lead on your scope probe because the neutral and the earth are connected at the circuit breaker.

I would, in general, recommend that an isolation transformer always be used for doing any live testing on a set, no matter how safe you think you're being, but I know not all people will do that.

Sorry if this is unneeded advice, but I just wanted to make sure that at least someone said this to you.


IIRC all Zenith CCIIs, besides the one flat chassis variant that had a switch mode module, had a big honking power transformer with full isolation so you don't need an outboard isolation transformer on these.
Although transformers can short between windings and keep working as though nothing is wrong (I had my outboard bench isolation transformer do this to me and ironically cause the very problem it existed to fix... I learned the hands on way) and it's wise to check chassis to scooe ground voltage with a DMM before hooking up a scope.

IIRC all Zenith CCIIs, besides the one flat chassis variant that had a switch mode module, had a big honking power transformer with full isolation so you don't need an outboard isolation transformer on these.
Although transformers can short between windings and keep working as though nothing is wrong (I had my outboard bench isolation transformer do this to me and ironically cause the very problem it existed to fix... I learned the hands on way) and it's wise to check chassis to scooe ground voltage with a DMM before hooking up a scope.

Yeah, I just automatically use my isolation transformer for any DUT. Even with an internal transformer, you still have mains on the hot side of the power supply, and accidents can happen

I decided I would give my battery operated scope a shot at it. I do know that back in 2012, I scoped just about everything major on it with my Tektronix before anyone mention "hot" chassis. I did inquire about it after reading that and had mixed responses about using an isolation transformer. Some said it was ok not to since it had a transformer for all sources of power, while others said it was better safe than sorry. I am in the camp of better safe than sorry, so I'll be using battery operated and only if that doesn't work will I bring out the big gun.

Maybe someone can tell me if I have this correct.... I want to scope the B+ DC coupled. If I then do AC, won't that show me ripple? If so, how much ripple is too much ripple? The filter caps for the B+ came off the canister cap, but other than the values in it, I can't find anything about ripple. I do know about what I replaced it with and it has a ripple of 1.5A. I don't know if that's too much, but all the caps I could find were between 1.4 and 1.6A for ripple. I've learned quite a bit over this project, but somethings still mystify me.

Some said it was ok not to since it had a transformer for all sources of power, while others said it was better safe than sorry.

Yes, it's a better safe than sorry thing. The issue could arise if you accidentally touched something that is on the line side of the transformer. If that happens, it will short out your probe ground to line voltage.

However, if you were to accidentally touch the line side of the transformer with you hand, you could then be connected to the breaker yourself, and that could hurt or kill you. This is generally why some people recommend an isolation transformer no matter what. I do enough electronic repairs that I bought one and just use it.


Maybe someone can tell me if I have this correct.... I want to scope the B+ DC coupled. If I then do AC, won't that show me ripple? If so, how much ripple is too much ripple?

I feel like I would start getting suspicious if it was more than 100mV, as that might indicate weak filter caps. If it's much over 150-200mV that would make me concerned, and any much higher than that I would turn it off and start hunting for the bad component. Certainly if it was over 1V or more.

In terms of AC Vs DC probing: The DC probing doesn't show the ripple because you have to crank up the volts/div so high that you lose the visual resolution to see the ripple. Looking at AC only means the DC component is gone, and you are then just looking at the waveform centered in the middle of the scope (vertically). So that's why you see the ripple in AC coupled.

I don't know what that particular set looks like, but my 1975 Sony 9" is about the older thing I have and it's B+ is rock solid at 130V with less than 20mV of ripple, so I know it's possible.

Yes, it's a better safe than sorry thing. The issue could arise if you accidentally touched something that is on the line side of the transformer. If that happens, it will short out your probe ground to line voltage.

However, if you were to accidentally touch the line side of the transformer with you hand, you could then be connected to the breaker yourself, and that could hurt or kill you. This is generally why some people recommend an isolation transformer no matter what. I do enough electronic repairs that I bought one and just use it.



I feel like I would start getting suspicious if it was more than 100mV, as that might indicate weak filter caps. If it's much over 150-200mV that would make me concerned, and any much higher than that I would turn it off and start hunting for the bad component. Certainly if it was over 1V or more.

In terms of AC Vs DC probing: The DC probing doesn't show the ripple because you have to crank up the volts/div so high that you lose the visual resolution to see the ripple. Looking at AC only means the DC component is gone, and you are then just looking at the waveform centered in the middle of the scope (vertically). So that's why you see the ripple in AC coupled.

I don't know what that particular set looks like, but my 1975 Sony 9" is about the older thing I have and it's B+ is rock solid at 130V with less than 20mV of ripple, so I know it's possible.

I don't know what the ripple is, it was more a question about the ripple noted for the capacitor. I'm assuming that's the maximum ripple current the capacitor can/will pass. While my jailbars have reduced in intensity, they are still there. All the Zenith jailbar fixes I can find aren't for this chassis, but they all point to filtering capacitors near the power transformer. So I'm hoping it will be one of the caps in that area.

I'm going to start testing voltages tomorrow. Right now I'm installing an IC socket and new IC on the sound board in hopes of restoring tone control. I've check the wiring and pot and it all appears good. That leave the IC as the tone control goes directly into pin 1 of the IC. Seeing as how the IC on the Chroma board caused tint and color saturation issues, I'm willing to take an 8$ gamble and install an NOS IC.

I don't need a fancy isolation transformer, do I? There's a unit on Amazon for 136 and it seems decent for the price. It handles 500W. Is that good enough, or it is wiser to get the 2000W version? I'm not sure if this set exceeds the 500W unit's 4A.

Not that this is the cause of my loss of tone control, but it shows how things fall through the cracks. It's been working this way for 52 years, but they could have done better. "Quality goes in before the name goes on...."

Obviously bad connections, easily reflowed and cleaned up. Could very well be your problem. You will know soon enough.

I usually find the 125v B+ in the flat pan chassis such as your 25EC to be 120-130 depending on the line voltage. IIRC this supply is regulated by the resonant circuit formed by the power transfomer and the 3.3uf oil capacitor. There is no regulator that you can adjust. The 24v supply does have a regulator, set by the zener diode in the base circuit.

If your jail bars are vertical, as they typically are, the "ripple" is at a horiz rate leaking into the video, more likely the boost source.

Are you looking at Sams? Which one? or the Zenith CM?

Ripple current rating of a cap usually isn't tied so much to B+ ripple voltage as it is to series current. Without seeing the schematic I can hazard a guess that the cap with that rating is either the resonant cap in the transformer or it's a series AC pass cap in a B+ doubler circuit. Ripple current in a cap usually means that that caps primary duty is not so much to filter DC as it is to pass large amounts of AC power along to somewhere else. Some B+ doubler circuits the main B+ cap does double duty and is there to handle large AC current and filter DC.

Obviously bad connections, easily reflowed and cleaned up. Could very well be your problem. You will know soon enough.

I usually find the 125v B+ in the flat pan chassis such as your 25EC to be 120-130 depending on the line voltage. IIRC this supply is regulated by the resonant circuit formed by the power transfomer and the 3.3uf oil capacitor. There is no regulator that you can adjust. The 24v supply does have a regulator, set by the zener diode in the base circuit.

If your jail bars are vertical, as they typically are, the "ripple" is at a horiz rate leaking into the video, more likely the boost source.

Are you looking at Sams? Which one? or the Zenith CM?

I'm using Sams. Been unable to find the Zenith.

I'm attaching a couple pics of the main transformer and circuits as well as the horizontal and boost circuits. I'm getting better at using schematics, but get a bit lost seeing multiple voltages coming from the transformer to different points and combining and turning into completely different voltages. For instance, the voltage going to the Chroma module is 125V, but in the schematics, it is derived from two 100VAC lines, one 235VAC line. Don't get me started on the return of it going to a separate line derived from 26VAC line to a voltage regulator creating 23.5V. :lmao::confused:

Ripple current rating of a cap usually isn't tied so much to B+ ripple voltage as it is to series current. Without seeing the schematic I can hazard a guess that the cap with that rating is either the resonant cap in the transformer or it's a series AC pass cap in a B+ doubler circuit. Ripple current in a cap usually means that that caps primary duty is not so much to filter DC as it is to pass large amounts of AC power along to somewhere else. Some B+ doubler circuits the main B+ cap does double duty and is there to handle large AC current and filter DC.

Do wish they canister cap had it's main function noted and more about it's specs.

Also, in the horizontal section, I replaced the damper diode (CR218 on previous post pic) on the HOT and lifted the leg of the boost diode (CR219) and it tested good, but I'm not sure if that excludes it from being an issue. The only things left in that area would be all the ceramic caps around them and the resistors. I remember someone, some time ago, saying that ringing is reduce/removed by using diodes and caps and if one part of the circuit is bad our out of spec, ringing can return.

Just checked the B+ 125V and got 129.2V from the test point and 129.1 from the Chroma module through the last module to the return point. So I'm assuming that is good. Also, the scope showed around 1V AC on top of the 129V DC. Not sure if that's good or bad.

Oh, and I reflowed the solder on the sound IC, but it didn't help. I took it out, put in a socket and installed the new IC. I now have tone control again. One more misc issue down.

I realized now that I forgot about what I had done years ago to the boost circuit. I replaced the boost rectifier, tested the resistor, but never changed the ceramic capacitor as I couldn't find the correct replacement. Zenith uses a 600pf 2kV and I couldn't find any NOS and for new all I could find were 560pf or 680pf. The same for the HOT. I replaced the damper diode, but not the capacitor for the same reason.

I know Zenith chose that value for a reason, but I don't know how important that exact value is to the circuit. It's the last thing I can think of that might be causing the jailbars.

Do you have a picture you can post of a blank raster?

Assuming this is Sams 1370, take a look at C270 10uf 300v on the 240v boost supply from the Horiz Out Transformer. That boost source feeds the RGB Video outputs.

Did I understand correctly the "jail bars" are intermittant?

Do you have a picture you can post of a blank raster?

Assuming this is Sams 1370, take a look at C270 10uf 300v on the 240v boost supply from the Horiz Out Transformer. That boost source feeds the RGB Video outputs.

Did I understand correctly the "jail bars" are intermittant?

No, they aren't intermittent. They are always there, but can be reduced by bring down brightness and contrast to an unusable level. :thumbsdn:

Posting a pic from the DVD player screensaver.

I have a new 10uf 300V capacitor on hand as I want to replace them all again to ensure I have the correct replacements installed. I replaced them 13 years ago, but I didn't have the SM, so I ordered solely based on value. This time I used the part numbers from the SM and got all but one based on that info. The other one is supposed to be 25uf 15V non-polar, but the SM has no part number and all I could find was a 22uf in non-polar.

I'm attaching a pic of the section with C270. Out of this section, my concern is C258 in the pic (small gold radial). I'm trying to go back in memory as to why I used a Nichicon radial of the type I used for restoring my Pioneer SX-1080. Not sure what that cap does, exactly, but I would assume it is up to the task. Still, I ordered the correct replacement for it as well.

The C270 I left the leads long so I could position it better after the safety capacitor upgrade. Don't know if the longer leads affect anything.

This might not look good, but it is possible to parallel four 150pf 2kV capacitors to make the 600pf I need, right? I've found 3 I'd like to replace (flyback, HOT and boost sections). It's impossible to find 600pf and anything close is either higher or lower.

You could, if that's what you have.

Very low value film caps don't tend to come in high voltage variants, but ceramic capacitors do. Some cap types are chosen for a specific purpose, and can't be changed, but that's not always the case. Ceramics, especially very old ceramics, tend to drift in value with temperature a lot, so they aren't used when the value has to be really specific, but newer ceramics of high stability types will do very well at this point, and can be subbed for films in many places. Maybe not a good idea if it's a tuning cap.

There's a very stable Y5R 680pF cap: https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/F681K39Y5RP6UK5R/2831053

But I can't comment on the specific place in the circuit that your cap is in. Someone else will have to confirm that 680 is okay, and that the small amount of drift isn't a problem.

You could, if that's what you have.

Very low value film caps don't tend to come in high voltage variants, but ceramic capacitors do. Some cap types are chosen for a specific purpose, and can't be changed, but that's not always the case. Ceramics, especially very old ceramics, tend to drift in value with temperature a lot, so they aren't used when the value has to be really specific, but newer ceramics of high stability types will do very well at this point, and can be subbed for films in many places. Maybe not a good idea if it's a tuning cap.

There's a very stable Y5R 680pF cap: https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/F681K39Y5RP6UK5R/2831053

But I can't comment on the specific place in the circuit that your cap is in. Someone else will have to confirm that 680 is okay, and that the small amount of drift isn't a problem.

Since they're caps in the flyback and horizontal circuits, I thought they might affect the signal and cause ringing. If they don't serve such a purpose, then I'll leave them be.

Found issue with one cap. It's in the wave shape section of the Vertical Output section. The cap in there I tested and it's was at the low end of tolerance (81uf of 100uf), so I decided the new cap would go in. Upon looking up the schematic, I noticed that the cap is in backwards. The schematic shows the positive side connected to the diode and the negative to the resistor. It occupies the same connect points as R292 and one leg of R293. I've attached a pic of how it was and the part of the schematic. In the pic you can see the negative side of the cap connected to the diode.

Am I interpreting the correctly? Even in the SM, the crappy pic of the underside it appears that the positive side is down on the diode side.

I traced the path exactly as the schematic shows. The green/red lead connects to the diode, the other end of the diode connects to both the positive side of the capacitor and 470ohm resistor. The other ends of the capacitor and resistor join up with the lead of the 68ohm resistor and the other end of that resistor meets up with an orange wire that goes to pin 6 of J201. So if the last cap was put in backwards, why didn't it fail or cause issues with the circuit?

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

Am I interpreting the correctly? Even in the SM, the crappy pic of the underside it appears that the positive side is down on the diode side.

Agree with BeamT about the cap.

However, 80% wouldn't generally cause a circuit to fail. It's an indication that it might be on the way out or that it was stressed (possibly from being in backwards), but it wouldn't generally be the actual cause of anything not working.

On the other hand, 80% and high ESR could cause something to fail if the ESR is high enough. You can imagine ESR as adding a resistor in the circuit across the capacitor, which will throw things off by creating voltage dividers and stuff.

Long story short, check ESR if you're troubleshooting. Capacitance is only telling you part of the story.

Okay, I managed to find an under chassis pic from when I first got the set, before any work. The cap is definitely installed positive side to the diode. In the second pic, it is after the recap. The recap was done for me by a family member as my soldering skills were pretty non-existent at that time. The cap was put in backwards as the negative stripe side is to the diode. The replacement cap was also quite a bit smaller. The replacement I have, that I just installed per schematics (positive to the diode) is quite a bit larger and near the size of the original. The new cap is the Sprauge part number in the SM.

I have been having issues with doing proper convergence, but the pot that was bad wasn't the one connected to this lead and the other one that I want to replace causes the screen to shimmy during adjustment and sometimes continue to shimmy afterwards. I'll just replace that one and give another cleaning to the rest and see if this reversed cap might be the issue with convergence.

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

Your SM shows what mine does. I've posted two more pics of before and work and after the first recap. I am doing the second recap with part numbers from SM.

I've tested the resistors and they are at correct values. The diode passes 572 one way and infinite the other. So it seems the diode is good.

Agree with BeamT about the cap.

However, 80% wouldn't generally cause a circuit to fail. It's an indication that it might be on the way out or that it was stressed (possibly from being in backwards), but it wouldn't generally be the actual cause of anything not working.

On the other hand, 80% and high ESR could cause something to fail if the ESR is high enough. You can imagine ESR as adding a resistor in the circuit across the capacitor, which will throw things off by creating voltage dividers and stuff.

Long story short, check ESR if you're troubleshooting. Capacitance is only telling you part of the story.

I have been checking ESR as well as value. The one I removed had an ESR of 540 milliohms with a 100K frequency.

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

Would it be possible for you to post the adjustment section of the CM-122? I want to see if it compares to the Sams, or if it has better/different procedures.

Horiz ringing and jail bars in my experience can be very difficult to troubleshoot. Sometimes I've had good luck with a scope, if you want to try that route. The source can be a number of places and can be very subtle. Otherwise I have had some success examining one circuit at a time. I try not to just throw parts at it.

To finish where you left off, I would look at:

C258 10uf 50v B+ Horiz Module (you mentioned above)
C264 47uf 10v Secondary Horiz Drive Transformer

and then work your way through the horiz blanking and then into the video path. This could easily be caused by horiz blanking.

I find it helpful to work with a blank raster, from a known good generator, tuner mid channel, or IF disconnected. Chromatic switch off, color off. This eliminates any outside source issues and gives you a good baseline.

Has this set always had the jail bars? Has the tripler been replaced? Zeno (RIP) always commented on non-Zenith HV triplers causing Jail Bars. I never encountered this but after replacing a separate tripler and focus divider in a 25DC56 with a Zenith combined unit 977-36, I ended up with jail bars. Putting the separate tripler and divider back in, eliminated the jail bars.

What part of the CM-122 Set-up procedures are you looking for? or all of it.

Safety first, the boost circuits is these sets are not only at a higher voltage, they can deliver some current, lots of RF energy.

Horiz ringing and jail bars in my experience can be very difficult to troubleshoot. Sometimes I've had good luck with a scope, if you want to try that route. The source can be a number of places and can be very subtle. Otherwise I have had some success examining one circuit at a time. I try not to just throw parts at it.

To finish where you left off, I would look at:

C258 10uf 50v B+ Horiz Module (you mentioned above)
C264 47uf 10v Secondary Horiz Drive Transformer

and then work your way through the horiz blanking and then into the video path. This could easily be caused by horiz blanking.

I find it helpful to work with a blank raster, from a known good generator, tuner mid channel, or IF disconnected. Chromatic switch off, color off. This eliminates any outside source issues and gives you a good baseline.

Has this set always had the jail bars? Has the tripler been replaced? Zeno (RIP) always commented on non-Zenith HV triplers causing Jail Bars. I never encountered this but after replacing a separate tripler and focus divider in a 25DC56 with a Zenith combined unit 977-36, I ended up with jail bars. Putting the separate tripler and divider back in, eliminated the jail bars.

What part of the CM-122 Set-up procedures are you looking for? or all of it.

Safety first, the boost circuits is these sets are not only at a higher voltage, they can deliver some current, lots of RF energy.

This set has always had jail bars to some extent. It was initially recapped because of other odd video issues associated with bad caps. Once the recap was done, the bars were more noticeable once brightness and contrast were set.

I have replaced C258 with the SM replacement part from Vishay. C264 tested good with and ESR around 430 milliohms and a value of 45. I have a replacement, just in case.

I've been trying to figure out where to inject the signal from my generator, but lack the knowledge of where in the circuit to inject it and what I need to disconnect when doing so.

Years ago, you can search for them, I posted quite a bit during the initial repair and search for ringing source. I used the scope of many areas and found ringing in a couple, but was told that it wasn't the cause of an issue. Found it in the brightness limiter circuit, HOT base and B+, but I was pretty new with the scope and I went with it not being the jail bars. The waveforms in the Sams aren't the highest quality, but enough to note difference is what I got.

The set has the original tripler. Only thing it need was the focus divider and I got an NOS and it's been fine ever since.

Once the set is back up and running, it's going to need some adjustments, so I thought I'd run through all the adjustments for AGC, ACC, APC, brightness limiter, color killer, convergence (static and dynamic), etc. Not going to mess with the IF stuff, just the basic stuff. Just wondering if the factory SM has the same procedures.

Thanks for all you time and help!

Well trying to test all the pots on the convergence board isn't going to work. I was able to test 3 correctly. Those 3 had correct values and smooth readings. The other 6 didn't show anything useful. I'm assuming it has to do with those 6 being tied into a bunch of resistors, diodes and many connected to each other. One started around 1ohm and gradually moved up to almost 30ohms, but instead of continuing upwards, it started to go back down and was almost 2ohms at the other end. I know this isn't supposed to happen, so it must be the other connections on the board interfering?

So I just gave them another dose of D5, followed by multiple turns and finished up with F5. If that doesn't help, I have several new pots I can install, but will need to get some Mallory pots noted in the SM as I can't find the ones I don't have. What I find odd is there is one pot that has specs of 120ohm 2W, but it has a different part number than the other three 120ohm 2W pots on the board. They all feel wire wound, so I wonder what the difference is.

Topside is done. It has all new transistors (2nd and 3rd video amps, brightness limiter, vertical blanker, blanker and video outputs). Might be a little overboard, but I had access to them, so why not. Also used contact cleaner on all the modules and IF contacts as well as all contacts in the plugs. With the replacement video outputs I was able to reinstall the original heatsinks and support cage.

and then work your way through the horiz blanking and then into the video path. This could easily be caused by horiz blanking.

In the horizontal blanking, all the resistors were replaced and the diode tested good. Is it possible for a diode to test good and be weak?

While troubleshooting by substitution can be a strategy, replacing large swathes of parts can have a real risk. At some point in time you can find yourself with a set that doesn't want to work right, and unraveling layers of parts and changes can be extremely difficult.

In the end this is your set and your journey!

Always wait for the DeoxIT to evaporate and dry before you energize.

Diodes can be leaky, the horiz blanking diode CR201 would be a good part to substitute. This needs to be a fast switching diode like a ECG177.

I would take some time to look at the voltages on the Blanking Amp Q202, Vertical Blanking Amp Q217, and 3rd Video Amp Q203. The line between the collector of Q217 to the base of the Blanking Amp Q202 gives you a perfect place to scope the blanker at both the vert and horiz rates. Good waveform to look for in the SAMS. C204 and C202 are critical to horiz blanking.

Were any of the resistors in the Blanking circuit out of tolarance?

Out of curiosity does the Peak Pix control work?

Does this set have a separate focus divider?

Do you have the shield for the Subcarrier module?

While troubleshooting by substitution can be a strategy, replacing large swathes of parts can have a real risk. At some point in time you can find yourself with a set that doesn't want to work right, and unraveling layers of parts and changes can be extremely difficult.

In the end this is your set and your journey!

Always wait for the DeoxIT to evaporate and dry before you energize.

Diodes can be leaky, the horiz blanking diode CR201 would be a good part to substitute. This needs to be a fast switching diode like a ECG177.

I would take some time to look at the voltages on the Blanking Amp Q202, Vertical Blanking Amp Q217, and 3rd Video Amp Q203. The line between the collector of Q217 to the base of the Blanking Amp Q202 gives you a perfect place to scope the blanker at both the vert and horiz rates. Good waveform to look for in the SAMS. C204 and C202 are critical to horiz blanking.

Were any of the resistors in the Blanking circuit out of tolarance?

Out of curiosity does the Peak Pix control work?

Does this set have a separate focus divider?

Each of the subs were tested earlier in the set. I swapped them in and out until I was certain they all worked as expected. Just never go around to doing the permanent swaps. Now I have and it won't be hard to figure out which one if any fail. I still have all the previous parts.

I can scope them again. I did this back in 2013 on all those outputs and they measured at rated voltages. I also replace CR201 back then and still have the one I removed as the new one didn't help issues, so the old one is still good. Last go around I replaced the 750V Boost diode, Damper diode and Horizontal Blanking. The only other diode I was supposed to change, but didn't, was CR202 Zener Diode 24V across the emitter and collector of Q204. I have that diode and it would be an easy swap.

I'm going to order those two capacitors you noted as I was eyeing them myself, but is wondering what other pieces I might want as I'd like to maximize the order to justify the crazy shipping rates now.

The peak Pix works, the resistors in the horizontal blanking circuit were replaced and it does have a separate focus divider. I replaced that shortly after getting the set as it would sizzle on humid days and upon inspection it was drying and cracking.

Do you have the shield for the Subcarrier module?

This is the alternate module (9-69) for this chassis and it doesn't require the shield. If you look closely at the board, there is a shield around the sensitive section only. I think the cover is the reason the pots on the original were messed up. They were poking through the holes for make adjustments and messed the up. They were pretty mangled.

Do know if this set will run with the video IF module removed? If so, I can connect my generator's signal via it's injector connection directly to the C1 test point into the video amp section. I am unsure if connecting my generator to this point while the IF is working would be a bad thing as it seems there's roughly 6V on it. This would let me see if the jail bars are being injected from the IF stage.

I believe you can run this set without the IF module in place. The 125v B+ supply interlock does not run through the IF module. You wouldn't need to feed a signal to the IF output, you should still have a raster. You might need to turn the brightness up a bit to see it.

If you are going to replace C202 in the horiz blanker, it needs to a temperature compensated N750 Capacitor.

I believe you can run this set without the IF module in place. The 125v B+ supply interlock does not run through the IF module. You wouldn't need to feed a signal to the IF output, you should still have a raster. You might need to turn the brightness up a bit to see it.

If you are going to replace C202 in the horiz blanker, it needs to a temperature compensated N750 Capacitor.

If by the IF output you mean connection 5 on the IF module (Video-Sync-Chroma), that's where TP C1 is located, so I could clip the lead of the generator onto that point on the top of the chassis.

I have the two capacitors in my cart now and they are the part numbers from the SM and the C202 replacement is N750.

Here is the section of the generator instructions related to injecting the video signal. Maybe it will help identify exactly where it should be connected.

I'm assuming you have the set back up and running, and the jail bars are visible.

Try this:

1) Gently disconnect the IF Input cable from the tuner to the chassis. At the chassis it is very similar to an RCA connector. Power up, jail bars still visible? Power down.

2) Remove the IF Module. Power up, jail bars still visible? Power down. Leave the IF Module out.

3) Drive the video stages with one of your generators. Most generators will block a small amount of DC but to be safe, connect the 50 Ohm video output through a .1 uf or so capacitor to block the DC. Connect to the C1 test point you have identified. Shield to a nearby chassis ground. Power up, adjust video level from the generator, try different patterns, what do you see?

Safety-- This is a transformer based set, so you should be reasonably safe using grounded test equipment, unless something is seriously wrong.

I appreciate my Sencore PR57 everytime I use it:yes:

I'm assuming you have the set back up and running, and the jail bars are visible.

Try this:

1) Gently disconnect the IF Input cable from the tuner to the chassis. At the chassis it is very similar to an RCA connector. Power up, jail bars still visible? Power down.

2) Remove the IF Module. Power up, jail bars still visible? Power down. Leave the IF Module out.

3) Drive the video stages with one of your generators. Most generators will block a small amount of DC but to be safe, connect the 50 Ohm video output through a .1 uf or so capacitor to block the DC. Connect to the C1 test point you have identified. Shield to a nearby chassis ground. Power up, adjust video level from the generator, try different patterns, what do you see?

Safety-- This is a transformer based set, so you should be reasonably safe using grounded test equipment, unless something is seriously wrong.

I appreciate my Sencore PR57 everytime I use it:yes:

Set isn't together yet. I'm waiting for the C202 and 204 replacements. Am also going over everything under the chassis to make sure I didn't disturb something and create a short. Once that is done, it goes back together on Monday or Tuesday, depending on delivery of parts.

The instructions with the Hickok says to ground the generator by connecting black lead to chassis. I wish it had more details on that since I had assumed the black lead went with the red lead which is the trigger out for my scope. That and I'm sure it needs another adapter of sorts as my scope's trigger input is a 1Mohm 20pf BNC. But that's another day's battle.

Tried to pull C202 and 204 by heating up the bucket and pulling the leads out, but that only worked on one lead that was alone in the bucket. All the other leads were in one with multiple leads and I couldn't seem to get it hot enough as they all acted as heatsinks. So I cut the other leads.

I tested them and the 68pf tested as 56pf with an ESR of 21kohms and the .0047 tested as .0038 with an ESR of 411ohms. I tested them for value at 100Hz and ESR at 100kHz. That is correct? When the new ones arrive, I'll check them the same way.

I tested them and the 68pf tested as 56pf with an ESR of 21kohms and the .0047 tested as .0038 with an ESR of 411ohms. I tested them for value at 100Hz and ESR at 100kHz. That is correct? When the new ones arrive, I'll check them the same way.


Yeah, that ESR sounds way too high at 100kHz.

It's worth noting that you would have to have a fairly expensive and fancy tester to get a really accurate reading on something as low as 68pf, but I think it's safe to say that those are bad ~kohms, or 411ohms.

You should test the new ones before you put them in to see if your meter might be misleading you for some reason. Cheaper testers might not be able handle really small value caps. If the new caps also test crazy high ESR, then you know something's up

Yeah, that ESR sounds way too high at 100kHz.

It's worth noting that you would have to have a fairly expensive and fancy tester to get a really accurate reading on something as low as 68pf, but I think it's safe to say that those are bad ~kohms, or 411ohms.

You should test the new ones before you put them in to see if your meter might be misleading you for some reason. Cheaper testers might not be able handle really small value caps. If the new caps also test crazy high ESR, then you know something's up

It was kohms. I did read that lower values and higher voltage ceramics don't measure will with basic ESR testers. I will definitely test the new ones and compare the reads to see if my tester isn't up to the task.

I do have a question you might be able to answer. The chassis is hand built, so when they are building them is there instructions on lead length for certain components, or is the length determined by fit and clearance? The reason I ask is the 68pf was pretty much bottomed out on the pad, so I had to clip it as high up toward the body as possible, leaving short stubs sticking out of the buckets. I plan on sitting the new leads into the bucket and using a small tip to reach the inside of the bucket and then flowing more solder into it. Since this cap had very short leads, do I need to do the same or can they be longer? I wasn't sure if they were short based on design or just that the cap fit better lower down. I know, odd question.

The chassis is hand built, so when they are building them is there instructions on lead length for certain components, or is the length determined by fit and clearance?

That would be determined by best practices at the time. Lead length could absolutely make a difference in specific situations, but I'm not familiar enough with the make of your TV in general to know all of the spots that would be sensitive. I would assume that anything involved in a trimmer circuit would be important as they could pick up interference.

The older guys in the Solid State forum will be able to tell you a lot better as they know the 70s US make stuff really well and I don't.

Manufacturing practice was to make a prototype agreed on by the engineering and production departments, and install it on the assembly line for physical comparison. The prototypes could range from individual modules to complete chassis in a plastic housing to illustrate it completely finished including things like lead dress of the wiring. No deviation was allowed whether it was actually important or not.

So in some cases, lead length was just a matter of neatness, and in others it had an effect on performance. Wiring harness lead dress could be important if it affected issues like jail bars, or it could just be an issue of neatness or easy order of assembly. And of course there were also consideration of tie-downs for long leads and heavy components to prevent breakage during vibration and shipping tests.

You can see these kind of considerations in the old Heathkit assembly manuals, where you are told to connect this or that but not solder it yet because something else will be added in the net step.

Good information. I will try to keep the leads of the 2 replacement caps as close to original lead length as possible. They are in the Horizontal Blanking circuit tied to the diode and also to the setup side of the setup switch. As you may remember, I can't get the setup mode to produce anything but a faint blue line at full and nothing from the other guns at full. I have to adjust with a greyscale ramp pattern and with the setup in normal mode, same max rotation of the G2s brings up a super bright raster, so I know the controls work.

+1 old_tv_nut, duplicate what was there as much as possible.

Stay on the track you are working, finish, and then move forward.

and I remember. Alternative Ways of Adjusting G2, is only 4 threads away. IMO you never fully explored that issue. ElectronicM gave you excellent advice and recommended looking at the voltages associated with the CRT. You looked at a lot of things but it appears you never returned to that. The CRT and Video Outputs are supplied by the 3 boost sources that are Horiz derived. The TV needs to produce 3 pictures, a red one, a blue one, and a green one, of equal intensity dark to light (gray scale -tracking) on top of each other (convergence). Thats why in the immortal words of Zeno, start with a good black and white picture.

I concede that a really tired/weak CRT might not be capable of producing one or more RGB setup lines but from the brief pictures you have posted, your CRT actually looks really good. Did you ever test the CRT?

ElectronicM has also chimed in with soldering advice, I think in more than one of your threads. Do you think you have enough wattage in your soldering devices? You should be able to pull component leads from the solder cones (pots), and re-insert leads to the depth of the cone. I use a Weller gun. If I did this more often, I would use the higher wattage iron that he uses.

+1 old_tv_nut, duplicate what was there as much as possible.

Stay on the track you are working, finish, and then move forward.

and I remember. Alternative Ways of Adjusting G2, is only 4 threads away. IMO you never fully explored that issue. ElectronicM gave you excellent advice and recommended looking at the voltages associated with the CRT. You looked at a lot of things but it appears you never returned to that. The CRT and Video Outputs are supplied by the 3 boost sources that are Horiz derived. The TV needs to produce 3 pictures, a red one, a blue one, and a green one, of equal intensity dark to light (gray scale -tracking) on top of each other (convergence). Thats why in the immortal words of Zeno, start with a good black and white picture.

I concede that a really tired/weak CRT might not be capable of producing one or more RGB setup lines but from the brief pictures you have posted, your CRT actually looks really good. Did you ever test the CRT?

ElectronicM has also chimed in with soldering advice, I think in more than one of your threads. Do you think you have enough wattage in your soldering devices? You should be able to pull component leads from the solder cones (pots), and re-insert leads to the depth of the cone. I use a Weller gun. If I did this more often, I would use the higher wattage iron that he uses.

I figured that since I'm replacing the C202 and 204, and they are connected to the setup side of the setup switch, it might help with that issue.

In the past, I tested all those voltages and they all were good. Since I haven't had any new issues that might point there, I haven't checked them again, but I can once it's back together.

The CRT is good. I've tested it a couple of times and each time it tests good and strong on all 3 guns.

My iron is 200W, but I might need to put the largest chisel tip on it for maximum heat transfer. Should I be concentrating the heat on the tip of the bucket, or the side? I think the side give more contact surface, now that I'm thinking about it.

I think for the setup switch issue, I might bypass it for testing. I've cleaned it a number of times, but it might be extremely dirty, or damaged. What I want to do is put it in setup and jumper the connections on the back side of the switch. That should determine if the switch is good or bad. The other area I need to look into is are the Chroma Gain Taps. I accidentally found out that while in setup I couldn't get a red line adjusting the G2 control, but I could by pulling the lead off the tap. I realized I had the tap on low when it should have been on Hi, so I pulled it to move it and a red line appeared. When I moved to Hi, the line went away. I tested the resistors in that network, but nothing stood out. I tried deciphering the schematic for that section, but I'm not sure what I was seeing.

+1 old_tv_nut, duplicate what was there as much as possible.

Stay on the track you are working, finish, and then move forward.

and I remember. Alternative Ways of Adjusting G2, is only 4 threads away. IMO you never fully explored that issue. ElectronicM gave you excellent advice and recommended looking at the voltages associated with the CRT. You looked at a lot of things but it appears you never returned to that. The CRT and Video Outputs are supplied by the 3 boost sources that are Horiz derived. The TV needs to produce 3 pictures, a red one, a blue one, and a green one, of equal intensity dark to light (gray scale -tracking) on top of each other (convergence). Thats why in the immortal words of Zeno, start with a good black and white picture.

I concede that a really tired/weak CRT might not be capable of producing one or more RGB setup lines but from the brief pictures you have posted, your CRT actually looks really good. Did you ever test the CRT?

ElectronicM has also chimed in with soldering advice, I think in more than one of your threads. Do you think you have enough wattage in your soldering devices? You should be able to pull component leads from the solder cones (pots), and re-insert leads to the depth of the cone. I use a Weller gun. If I did this more often, I would use the higher wattage iron that he uses.

I figured that since I'm replacing the C202 and 204, and they are connected to the setup side of the setup switch, it might help with that issue.

In the past, I tested all those voltages and they all were good. Since I haven't had any new issues that might point there, I haven't checked them again, but I can once it's back together.

The CRT is good. I've tested it a couple of times and each time it tests good and strong on all 3 guns.

My iron is 200W, but I might need to put the largest chisel tip on it for maximum heat transfer. Should I be concentrating the heat on the tip of the bucket, or the side? I think the side give more contact surface, now that I'm thinking about it.

I think for the setup switch issue, I might bypass it for testing. I've cleaned it a number of times, but it might be extremely dirty, or damaged. What I want to do is put it in setup and jumper the connections on the back side of the switch. That should determine if the switch is good or bad. The other area I need to look into is are the Chroma Gain Taps. I accidentally found out that while in setup I couldn't get a red line adjusting the G2 control, but I could by pulling the lead off the tap. I realized I had the tap on low when it should have been on Hi, so I pulled it to move it and a red line appeared. When I moved to Hi, the line went away. I tested the resistors in that network, but nothing stood out. I tried deciphering the schematic for that section, but I'm not sure what I was seeing.

I have tested all the resistors in the setup circuit from the switch to the convergence board. So don't know enough about reading schematics to understand why setup connects the video outputs to the inductor coils on the convergence board. I'm pretty sure when you flip the switch it's main function is to disconnect all the video amps and collapse the vertical.

I've also tested all the resistors in the gain taps and they are withing tolerances. So unless I'm missing something, my inability to bring up lines in setup looks to be either in the switch itself, or the connection of the outputs to the convergence board.

The side of the solder pot terminals usually works best. I recommend choosing the biggest tip for best thermal mass and conduction to the terminal.

The side of the solder pot terminals usually works best. I recommend choosing the biggest tip for best thermal mass and conduction to the terminal.

Got the biggest chisel tip ready to go. Replacement caps will be here tomorrow, so I should be able to get them installed, check over the entire chassis for anything I might have disturbed in my work and all new transistors for proper orientation. Then it's time to reinstall the chassis and fire it up. Fingers crossed.

I managed to get the other 3 leads from the cut capacitors out. It seems a bigger tip and holding in on the side of the solder bucket helped, but I think extra pulling also helped. I'm attaching a pic of one of the leads I got out. I'm not sure what that stuff is, but it is hard and was on the three leads I couldn't get out, but not on the one I did get out. So maybe that's why only one lead came out.

Also note the crud on the lead. Is that old flux? I'm assuming the discolored lead is only from the removal and it wasn't that way in the solder. :lmao:

So when I work to install the new capacitor leads, should I put a drop of flux in the bucket first? I figure I'll let it heat up for about 20 to 30 seconds before trying to insert the lead.

Oh, and with the amount of time it takes to head up the bucket to melt the solder, is the heat transfer to other components like resistors bad? They get pretty warm/hot during the process. Should I clip a heatsink to the leads of the other components sharing the bucket?

Question about transistors. I've noticed that several transistors noted in the SM, each with different Zenith part numbers, have PNs for other manufactures, but those part numbers are all identical. Does this mean when you buy from another manufacturer you're getting replacements that aren't the exact specs, but close enough to work? For instance, transistors 695, 888, 931 and 447 replacements are all ECG123A or NTE123AP. The same happens will all other manufacturer's replacements (RCA RT102).

Question about transistors.


So the thing about transistors is that they have a lot of characteristics, but which ones make a difference entirely depends on your application.

When a manufacturer is deciding which transistor to use in which spot, they have an entirely different set of considerations than a general repair-person does, or in fact you or I have many years later.

Usually, they are working with a bunch of boxes of parts they buy in bulk, and that is all down to contracts and maybe just what's around at the moment. They try to make it as cheap as possible while still doing the job, but that might actually mean using a way over-spec'd part if that's what they have a whole lot of in the back room right now.

The repair manuals are looking at the whole field of parts available and giving you choices because different repair shops have their own stock and their own prices based on the volume of parts they can afford to buy at the same time.

Sometimes (a lot of times) the exact transistor you chose doesn't make a heck of a lot of difference. As long as it sort of fits the voltage and current requirements as the junctions, it's going to do the job.

Other times, the gain characteristics and/or the transition time of the transistor is going to make a big difference, and you have to pay attention to it in the circuit. In these cases, even a single transistor replacement can require reverse engineering the whole portion of the circuit that it is found in.

If you are seeing a single transistor type shown as a replacement for many different transistors in BOM, then it's likely that is a common replacement part used for a variety of transistors from different manufacturers. And so is more of a general replacement than an exact fit. They are usually pretty much okay, but I have seen situations in which Sam's replacements didn't work in a circuit. Not often, but I've seen it.

So the thing about transistors is that they have a lot of characteristics, but which ones make a difference entirely depends on your application.

When a manufacturer is deciding which transistor to use in which spot, they have an entirely different set of considerations than a general repair-person does, or in fact you or I have many years later.

Usually, they are working with a bunch of boxes of parts they buy in bulk, and that is all down to contracts and maybe just what's around at the moment. They try to make it as cheap as possible while still doing the job, but that might actually mean using a way over-spec'd part if that's what they have a whole lot of in the back room right now.

The repair manuals are looking at the whole field of parts available and giving you choices because different repair shops have their own stock and their own prices based on the volume of parts they can afford to buy at the same time.

Sometimes (a lot of times) the exact transistor you chose doesn't make a heck of a lot of difference. As long as it sort of fits the voltage and current requirements as the junctions, it's going to do the job.

Other times, the gain characteristics and/or the transition time of the transistor is going to make a big difference, and you have to pay attention to it in the circuit. In these cases, even a single transistor replacement can require reverse engineering the whole portion of the circuit that it is found in.

If you are seeing a single transistor type shown as a replacement for many different transistors in BOM, then it's likely that is a common replacement part used for a variety of transistors from different manufacturers. And so is more of a general replacement than an exact fit. They are usually pretty much okay, but I have seen situations in which Sam's replacements didn't work in a circuit. Not often, but I've seen it.

Got it. Was just wonder as I needed two 695s and found a seller with a lot of 10 for next to nothing. So I bought them and wondered what I could do with the rest. If the ECG123A is a basic replacement for a number of transistors, and one of those is the 695, then if need be, I can use the 695 as a replacement for those other transistors?

Well it seems the replacement caps won't be here until tomorrow. No biggie as I was cleaning the G2 pots with D5 and F5 and decided to give the setup switch it's 5th or so cleaning when I decided to look at it closely with my video microscope. I couldn't see anything but the pads at the end for the setup mode and the contacts on the slider. They were pretty much black and it appeared the slider part wasn't making full contact even though the spring in it was providing pressure. Not sure this at fault, but it got me searching for a replacement and I managed to find an NOS switch and bought it. Should be in by end of week. So I'm going to replace the switch while the chassis is still out.

The G2s now rotate much smoother than before, so it can't hurt to have clean pots.

then if need be, I can use the 695 as a replacement for those other transistors?

If you show me a circuit (the schematic) with a transistor, and you give me both the original transistor and the one your are thinking about replacing it with (and their datasheets), then I can probably tell you with some confidence if it's going to work.

That's about the extent of my knowledge with this stuff; one at a time. I can't sign off on blanket replacements between transistors regardless of the use case. I'm not that good at it.

If you show me a circuit (the schematic) with a transistor, and you give me both the original transistor and the one your are thinking about replacing it with (and their datasheets), then I can probably tell you with some confidence if it's going to work.

That's about the extent of my knowledge with this stuff; one at a time. I can't sign off on blanket replacements between transistors regardless of the use case. I'm not that good at it.

Sounds good. I've tried to figure out which transistor package is from what year and if one is better than the other. For the 695s, I received 3 different package types, There are round white ones with black tops, black round ones that look like a water tower and the TO-92. I tried looking up the other 2, but I found no package numbers for them. I'm assuming the ones not TO-92 are earlier versions and might be of lesser quality.

The ones I'm looking at are the water tower looking one on the Horizontal module Q804 (121-447). Also, the Horizontal module is supposed to have a 121-931 (Q801), but there's a 447 in its place. Is this a suitable replacement, or is the 931 the best choice?

The ones I'm looking at are the water tower looking one on the Horizontal module Q804 (121-447). Also, the Horizontal module is supposed to have a 121-931 (Q801), but there's a 447 in its place. Is this a suitable replacement, or is the 931 the best choice?

Do you have the datasheets for the transistors? I looked around for them, but I can't find anything. I even went as far as doing a cross-reference on the an archived version of the NTE part cross-reference tool, but those numbers don't come at all.

I'm good enough to have an idea of which specs would be important to adhere to, but I can't tell you what the specs of the original transistor are without a datasheet.

In general though, both Q804 (waveshape) and Q801 (AFC) are not in super critical spots for either speed or gain. I would think that almost any decent modern transistor with the correct voltage requirements would do the trick. Something like a 2N4401 could work probably. Q801 would be more likely to have possible issues if the gain was too high because the AFC circuit might rely on the gain characteristics to lock in, but I can't tell you that because I don't know the gain of the original transistor.

It is ususal design process in transistor circuits to design for proper operation whenever the transistor current gain (beta) is above a certain minimum.

Looking at Q801, you see that the peak to peak waveform on the base is twice the size of the DC voltage, so this stage is being overdriven to clip the AC waveform. The DC bias uses feedback from the collector load. Given all this, it's likely that any general purpose transistor with a beta of say 100 or greater would work.

Looking at Q801, you see that the peak to peak waveform on the base is twice the size of the DC voltage, so this stage is being overdriven to clip the AC waveform. The DC bias uses feedback from the collector load. Given all this, it's likely that any general purpose transistor with a beta of say 100 or greater would work.

Ok. That's really cool of you to explain that. I think I get it.

I think what you're saying here is that because the voltage threshold is so low, the transistor is only going to turn on when the waveform crosses the conduction threshold. Which would be ~0.7V if the emitter was tied to ground, but it has a 270 ohm resistor there, so I guess it would actually be a little higher than .7 it starts, depending on what the voltage is on the emitter at any given time.

So that means the collector probably has a ~10Vpk squarish waveform with fairly short negative-going pulses when Q801 is in conduction, right?

Ok.
So that means the collector probably has a ~10Vpk squarish waveform with fairly short negative-going pulses when Q801 is in conduction, right?

I won't try to guess what the duty cycle is. I haven't seen this sort of frequency control before and I'm not sure how it works - maybe by varying the duty cycle?

I won't try to guess what the duty cycle is. I haven't seen this sort of frequency control before and I'm not sure how it works - maybe by varying the duty cycle?

If the collector is sitting at 8.72V, fed by the 23.5V, then I would assume that the resulting waveform is determined by the narrow window that the base waveform allows for Q801 to be turned on.

If the base is at .54V, and the emitter is at .27V, and the waveform on the base is 1.5Vpkpk, then that means the top of the waveform swing is like 0.90-1.29V, where Q801 is turned on I would think.

The collector is providing some weak feedback by being attached to the base through the resistor, so I suppose that would help with changes in current draw due to the reactance of the hor osc coil on the other side of the collector.

Maybe?

Well something happened that usually never does, but I was wanting replacement transistors for the horizontal and vertical boards, for now or the future. I kind of want OEM parts, but finding them all from once sources proved impossible. I could find them all, but buying individually with shipping on each was way more than I was willing to pay. Then it happened, something very rare. I searched for a 931 transistor and came across a listing I couldn't ignore. Not only did it have every single transistor I wanted, I also had a red G2 pot! It had a few other items that I might find a use for, but even if I don't, I got the entire lot for 16 bucks! I don't know if I need the red G2 pot, but now I can disconnect the current one for full testing and know I have a replacement if needed. I tried testing in place, but the readings were odd as it would go up, then down and back up again pretty consistently during testing. Not sure if being in circuit was the reason.

I got the new C202 and 204 capacitors yesterday 68pf and .0047pf. They test dead on, but still show a high ESR, so I now know my tester isn't up to the task for these values.


Tomorrow I carefully plan and execute the installation. I have my liquid flux, 200W iron and largest chisel tip I have and a couple clip on heat sinks for the leads of the resistors already in the solder buckets. Then by Friday I should have the new setup switch and have it installed same day. Once I go over all components to make sure I didn't disturb routing or created a short, back in it goes and I'll fire it up.

Been an interesting journey so far. Hopefully I've made things better, not worse. :thmbsp:

So now from update to question. I want to test voltages to the CRT and will pull socket back just enough to clip leads on all three of the screen drivers. Since they are driven by the 750 boost, I should get no reading higher than that and the SM has the voltages noted for each gun. However, if the G2s control those voltages, what is the purpose of noting those on the CRT part of the schematic? Since they G2s are adjusted for greyscale, doesn't that mean those voltages will be different based on current adjustment position? What exactly should I be looking for? Also, if I do the same for the cathode and G1? Are any of the values given in the SM a for sure value or will any of them vary and I'm looking for values close to what is stated?

Thanks!

Voltages given for the G2's are just what was measured on the particular set that was used and will vary with adjustment, as you said.
Voltages on the cathodes also vary with video content, so may be quite different if you use a different test pattern from the one used in the service info.
Volatages on the G1's also vary with video content in sets where the color difference signals drive the G1's.

Voltages given for the G2's are just what was measured on the particular set that was used and will vary with adjustment, as you said.
Voltages on the cathodes also vary with video content, so may be quite different if you use a different test pattern from the one used in the service info.
Volatages on the G1's also vary with video content in sets where the color difference signals drive the G1's.

So basically I'm just looking for something way out of the ordinary? :lmao:

I reinstalled the chassis after inspecting all components. I connected all internal cables and verified proper locations based on pics taken before removal. I plugged it in and it immediately started a deep buzz from the speaker. I unplugged it and double checked everything and it is all correct. Plugged it back in and it did the same thing. I have it unplugged now and haven't tried turning it on until I find out why it is making this sound while off. Any ideas?

Never mind, ground loop. First time it's ever happen. Rotated plug and it's gone.

I haven't gotten around to doing any real adjustments as the room is too bright. I'll do them this evening. The new setup switch is late, so I left the old one in for now. Still won't bring up any lines from the G2 controls. Hopefully the new one will fix that issue. As for jailbars, here's hoping the new caps will fix it. If not, I'm going to look at removing the IF module and injecting my generator directly into the circuit on C1. Was told these bars can also come form bad RF, IF, etc.

We're getting there!

I've done all the adjustments. I got the convergence pretty much dead on, except for a little blue horizontal on the very right edge. Seems the 2 new pots and a very extensive D5 and F5 cleaning of the other pots helped greatly. It is the best I've been able to get it and I'm more than happy with it and will not touch it again.

I'm starting to think the jailbars are coming from some other source (IF?). They are still there with all new electrolytics using SM part numbers, new diodes and new ceramics in the horizontal circuits. I disconnected the tuner to IF and I got a bright white raster, so no way of telling if the jailbars were there or not. My next step is to remove the IF module and connect my generator directly to C1 and inject the signal. I'm not sure if I can bring up anything that will show if the jailbars are there or not. What about a direct composite feed? I'm sure it's not as simple as connecting the composite out signal to C1 and ground, right?

As for the peak pix control... Is that off fully counter clockwise, or does that over soften the image? I really can't tell, but it seems soft CCW and noisy fully CW. So maybe the center is where it should be?

Attaching a couple of pics. They're from a laserdisc.

Peak pix action was designed to be default at center, with CCW notably softer and CW notably crisper.

Question about 23.5V in the set. How important is this? The reason I ask is I tested the regulator and it seemed fine. However, what I noted was the installed regulator is 121-808 and the sheet attached inside the set has it as being 121-966. In order to find the differences between them, I had to compare the part numbers from the other manufactures listed in the SM. That lead me to compare ECG152 (121-966) to the ECG184 (121-808). I found datasheets on them from AllTransistors and they are definitely different, but I don't know what those difference would translate to or if it's even an issue. Since this voltage is in just about every circuit of the TV, it must be important.

Can someone with the necessary knowledge take a look?

Thanks!

Since this TV has a transformer, it should be possible to bypass the IF and inject composite video and audio. If I understand this correctly, I should be able to remove the IF module, connect the composite to C1 and ground, then connect the audio to connection 4 of the sound module and ground. To reverse it, I just remove connections and reinstall IF module.

The input voltage of the sound module is .25V, down from the SIF out of .47V going through L215. I believe the fixed audio out of a DVD player can be as high as 2V, so will something need to be added?

I'm attaching the relative portion of the schematic and circled the points of connection.

I removed the IF module and connected the video out of my generator to C1 which is noted as being the picture detector output. The generator's manual says to connect its video output after the detector, so this is the correct point. When I did, I had to set the output on the generator to max in order to see anything. What I got was dim and the horizontal and vertical was not stable.

Looking over the schematic, the detector out is 6.99V. From reading up, the composite signal is a max of 1V. The detector's out also feeds the video processor module and that is 6.24V. The video processor module sends out H and V synch as well. So does the composite signal I'm feeding it need to go through the video processor as well to? I see 3 destinations for the detector output.... The video processor module, the chroma module and the section with the video amps, vertical blanker, blanker amp, etc.

So am I correct that the composite I feed needs to hit all those points and can't just simply wander into the video outputs. The signal needs to drive the vertical and horizontal modules, etc?

If this is the case, how do I duplicate the voltage on the detector output for all the other modules? The odd thing is, the manual for my generator says nothing about removing the IF module or anything other than connecting the lead to a point after the detector. So maybe there is something in the circuit of the generator to allow it to inject its signal over the detector's?

Such a crazy day.

Troubleshooting 2 issues, jail bars, unable to produce one or more service lines in setup.

When you disconnected the IF input from the tuner, jail bars yes/no?
When you removed the IF module, jail bars yes/no?
When you inject the video source from your generator at C1, IF Module out, jail bars yes/no?

The 6.99v shown at C1 in SAMS is a DC value, to the right 1.4v P2P is the waveform involved and is roughly what your generator is supplying. Not every set has a IF Module that can be removed.

The 24v DC supply is very important, 121-808 looks like a good sub for 121-966. Higher values and a different case, but looks good. You noted in prior threads the voltage at the test point was good. Did you replace this transistor before?

What is the "ground loop" you are referring to?

The strategy behind measuring the DC values on the CRT is to rule out a circuit issue and unfortunately implicate the CRT. You appear to have good gray scale with what you have, good focus, convergence is really good.

I've never worked on an Avanti, which I believe your set is, do these NOT have a Service Saver plate on the bottom?

Might be interesting to test your setup switch with your ohmeter before you go to the trouble of replacing it.

Troubleshooting 2 issues, jail bars, unable to produce one or more service lines in setup.

When you disconnected the IF input from the tuner, jail bars yes/no?
When you removed the IF module, jail bars yes/no?
When you inject the video source from your generator at C1, IF Module out, jail bars yes/no?

The 6.99v shown at C1 in SAMS is a DC value, to the right 1.4v P2P is the waveform involved and is roughly what your generator is supplying. Not every set has a IF Module that can be removed.

The 24v DC supply is very important, 121-808 looks like a good sub for 121-966. Higher values and a different case, but looks good. You noted in prior threads the voltage at the test point was good. Did you replace this transistor before?

What is the "ground loop" you are referring to?

The strategy behind measuring the DC values on the CRT is to rule out a circuit issue and unfortunately implicate the CRT. You appear to have good gray scale with what you have, good focus, convergence is really good.

I've never worked on an Avanti, which I believe your set is, do these NOT have a Service Saver plate on the bottom?

Might be interesting to test your setup switch with your ohmeter before you go to the trouble of replacing it.

When I disconnect the tuner to the IF, I get a bright white screen, and see no jailbars, but I don't see them with any of the bright test patterns, so I can't say for certain if they are still there.

When I remove the IF module, the screen goes completely black like the set is off, so no way to tell if jailbars are there.

Connecting to C1 with IF module removed doesn't bring up the pattern from the generator and if I increase the signal on the generator I get a scrambled image like there's no horizontal or vertical sync. Adjusting the vertical and horizontal hold makes it more stable, but it's not a useful image.

Since the manual for the generator doesn't specifically state the connection for injecting their signal needs the one from the IF be disconnected, I'm tempted to just leave the IF module in, disconnect the tuner and connect the generator to C1. The worst that can happen should happen to the generator, not the TV. I can't imagine they'd make such a feature and not implement safeguards in their system. Also, having the IF module removed might remove the 6V needed for something else in the video chain?

The regulator installed is what was installed when I got the set. Since it didn't match the paper in the set, I got the correct one. Never got around to installing it, but did so this time round as I had it. And yes, the voltages from the installed were correct and still so with the new regulator. I know I didn't need to change it, but it bothered me it wasn't what was called for.

I'm assuming it was a ground loop. After reinstalling the chassis and making all the internal connections (and double checking), I plugged it back in. It immediately made a deep buzzing from the speaker and possibly other sources. I immediately unplugged it and check all connections again. I plugged it back in and it still did it. I left it plugged in and tapped on all connections in the area of the tuner, IF and sound. I found that just my hand touching certain areas was enough to make it stop. That's what made me think it was a ground issue. I reverse the plug and it stopped and hasn't come back since.

What is a "service saver plate"? Never heard of it. Only thing on the bottom of the set is a removable metal cover to access the underside of the chassis.

I just got the new switch in the mail today. It is identical except for the fact it is much tighter than current one. The one in the set not only slides up and down, but in and out as if there were a spring between the slider and brass contacts. The new one has no play at all. Since all the resistors and capacitors on the setup side of the switch have been replaced, I don't know where else to look and changing the switch is an easy task that will help rule out another piece of the chain. This would also allow me to disassemble the old switch to inspect.

Tomorrow I plan on getting all the voltages from the CRT. I have it dialed in pretty well and thought I'd display the color SMPTE pattern with the pluge stuff on the bottom. That should keep voltages stable so if I test again I know the video information sent to the CRT is the same and any changes in voltage aren't from displaying different signal.

Zenith marketed the access plate on the bottom as the Service-Saver Chassis because it allowed service from the bottom of the set without having to remove the chassis. Components replaced, or measurements taken with the set running, tipped on its side.

With the IF Module removed, can you turn up the brightness and get a raster?

Yes, you can connect your generator 50 ohm video output to C1 with the IF module in the set. Rock or position the tuner slighlty to mid-channel, or you can remove the IF in cable.

Google "Servicing a 1974 Zenith 19DC12 4 tube hybrid color tv" you might find this YouTube interesting. No connection to the author.

Zenith marketed the access plate on the bottom as the Service-Saver Chassis because it allowed service from the bottom of the set without having to remove the chassis. Components replaced, or measurements taken with the set running, tipped on its side.

With the IF Module removed, can you turn up the brightness and get a raster?

Yes, you can connect your generator 50 ohm video output to C1 with the IF module in the set. Rock or position the tuner slighlty to mid-channel, or you can remove the IF in cable.

Google "Servicing a 1974 Zenith 19DC12 4 tube hybrid color tv" you might find this YouTube interesting. No connection to the author.

After all the times I've been inside the set I never noticed that there are 4 threaded inserts in each corner. I've never see an Avante with anything other than the plastic base, so I wonder what they are for. I was thinking of making some legs and screw them in so I can take off the base and open the bottom and not have to put the set on its side.

Okay, I'm going to give the generator to C1 with tuner disconnected as I am unable to set the tuner between channels as it's motor driven.

I'll also try upping the brightness with the IF removed.

Connecting to C1 with tuner, generator doesn't bring up anything useful. I can tell the generator is doing something as the screen changes a bit as I set the output level, but it never brings up anything even close to a pattern. With the IF removed, no amount of brightness setting brings up any raster, etc. I'm going to go over my pics of the underside and trace exactly where the IF out goes if not directly to C1.

I tried testing the voltage on the video out of the generator, but it only went up as I moved the output level and then dropped to 0 after moving it. I think I'll connect it to my scope and see if it actually putting out a composite signal.

If I'm not mistaken, I should be able to connect the center of a video out from my old DVD player to C1 and the outer to ground and get an image? I'm not worried about and if it works, I can let it go into screensaver mode as that really shows the jailbars.

I watched the video. Some interesting content. I've tested my CRT with 2 separate testers and each one shows it good. While I can't get a red or green line, I can get a faint blue line. However, if I do greyscale outside of the setup with a greyscale ramp, I can get very strong colors from each gun and good brightness. The thing I haven't been able to figure out is the gain taps. I understand they work through a series of resistors to help remove color from the white parts of the picture. If I am understanding the schematic correctly, if you pull the tap off, it disconnects the video output to the crt and that removes the 142V. So why, when I pull the red tap in setup do I get a bright red line and lose it when I put it back? Like I said, if I understand the schematic, why red line with 0V and no line with 142V

Rejuvenating is risky from what I understand. I don't want to run the risk of damaging the CRT.

There was one thing I didn't fully understand from the video. When he was reading voltage from each of the resistors, what exactly was he seeing that pointed to the CRT's blue gun? One side of all of them seemed to have the same 26xV and the other side of each had lower, with blue not matching what red and green showed. Not sure how that translates to a bad blue gun.

I'm posting a couple of screen shots. I have to admit this is the best the set has looked so far. These pics don't do it justice as I am getting better shots from the camera adjustments advised by others, but they are still a far cry from how good it looks in person. Got quite a few compliments on the image quality. The youngsters didn't know a CRT image could look this good. They thought all you'd see is large scan lines and blurry images. :lmao:

Tested the CRT again today and it tests as good and the image produced (color, brightness, contrast) seems to agree. So the inability to bring up lines in setup doesn't seem to be the fault of the CRT. Oh, and I got the greyscale set so well, I didn't have to touch the gain taps at all this time. Usually I had to move one and deal with the whites not as white as I'd like, but now they are pretty much dead on. Not too warm and not too cold.

Now if I can just get rid of the darn jailbars, I'd have a damn near perfect set.

What are the odds the jailbars are from the flyback? Reason I ask is I can get an NOS replacement for ten bucks. Even if it isn't the cure, are flyback usually something that hardly ever needs replacement, so a spare isn't necessary?

New question. I don't want to pull it again, but I find that the SM doesn't have anything on my tuner setup other than the remote board. I have no clue if the non turret schematics are for mine or not. I had it out months ago to fix the power on/off issue. I replaced all the trigger caps and other electrolytics on the board and it fixed the issue. I was just going over some pics I took and noticed that there is another board in the tuner/remote assembly and it has three electrolytics on it. I don't know if it's a board connected to the tuners or the board used for the channel tuners on the front side.

While on the subject of tuner, does an OEM IF module come pre-adjusted, or is that something that is done once installed and connected to the tuners?

Also attaching a pic of a piggybacked resistor that came in a batch of Zenith parts I got. It came in a plastic bag with no real indication on what it meant for.

The top resistor looks like 820 ohms +/-10%.

https://circuitdigest.com/calculators/5-band-resistor-color-code-calculator
decodes the 5-band resistor as 1.02 ohms +/-4%, which makes no sense to me.

Where did this batch of parts come from? Kind of seems like someone's bench sweepings unless someone can tell us what the 5-band device really is.

The top resistor looks like 820 ohms +/-10%.

https://circuitdigest.com/calculators/5-band-resistor-color-code-calculator
decodes the 5-band resistor as 1.02 ohms +/-4%, which makes no sense to me.

Where did this batch of parts come from? Kind of seems like someone's bench sweepings unless someone can tell us what the 5-band device really is.

It came in a plastic bag from Robert E Priebe Company Wholesale Electronic Distributor along with ohmite 470 ohm 3W resistor. Since all the other parts were Zenith, I figured it was some kind of Zenith "fix" for one of their TVs or radios. I tried looking it up, but band 5 was not helpful. Someone said it was probably a marking for military grading or such.

Pulled the tuner assembly. I figured out how it was assembled as it is a cluster that contains the remote board, UHF, VHF, motor and control as well as the tuner control center. The SM has only the remote board and that's in the supplemental add-on. The rest is not included. There are 4 electrolytics on it and I found another connected near the motor. My goal is to replace all the old caps, clean up all connections, oil the motor and put it back together. While I have no expectations this will help in anyway with the jailbars, I'm sure it can't hurt as the TCC is where the individual tuning controls are. I'm not sure what I'll find when I take the board off the back of the unit, but I'm sure there's something in there that might need cleaning/lubing as the motor turns something.

Wish me luck!

I haven't removed the remote motor yet as I'm still trying to figure out if I remove it, will it go back in smoothly. It has a strange toothed base that seems to be misaligned as the teeth mesh perfectly on the top, but seem to be off on the bottom. I can also see the particles from the tan part all over as it sheds/scrapes off. There is also a set of teeth on the base of the motor shaft that turns another gear next to it and a leaf switch. I know I need to find out what is wrong as half the time when I change the channel, it either gets stuck and I have to go back and forth to make it move, or it moves but takes a second or two to finish the rotation.

I'm attaching a couple pics in case someone has seen this setup before and can give some insight on what might be going wrong.

So who can tell me how this works?

I took apart the motor assembly to see why it sometimes doesn't change or seems to get stuck. The design seems to stump my brain, so I'm hoping someone here knows how and why it works. What really sucks is the one most important gear still seems functional, but I don't know how well it will last, if not forever. It is an odd design. The shaft is hard plastic, but the gear platter and teeth are flexible (to a point) and the back side is on the soft/grip side.

This is how it is configured. I've attached a couple pics. The motor shaft has a spring loaded black piece that has teeth up on the shaft that turns a gear and cam that activate leaf switches. I'm assuming this is how it knows it has gone the right amount to change one channel. Then the bottom of the black piece widens out and has two protrusions on the bottom that sit against the tan gear looking thing. That tan one is meshed with the black one on the bracket. The black one does not turn at all. It is keyed and sits in the bracket. So somehow, the motor turns and the black piece on the shaft turns on the tan one and gets it to turn, even though its teeth are meshed with the black one. Turning the black one by hand just makes it spin on the tan one, not make it move. So it can't be added pressure that makes it turn as that would force the teeth together tighter and never turn. Makes my head hurt.

Also, the tan gear has no part number and neither does the black piece over the motor shaft. The black on in the bracket does and I found one on ebay. Don't need it, but just curious if they exist. It would seem the tan one is a wear piece, so why no part number? Hmmm....

I'm starting to think the jailbars are coming from some other source (IF?).

Random jailbars in the raster is one of the very most difficult things to figure out.

From what I've been able to gather in my quest to solve jailbar problems in my own sets is the following:

1. They can be caused by missing shielding. Sometimes there were big metal shields covering things like the flyback or other noisy sections of the chassis, and they go missing during the life of the set
2. Sometimes grounding problems can cause them. This can also be caused by a missing ground that was completed by a shield or a poor connection on the tube itself or elsewhere.
3. In many cases, the jailbars were always there, and the reason you are seeing them is because newer components are somehow accentuating their visibility. I have been told by people more experienced than me that this can be due to fast, better performing parts passing through more of the bars. I would assume that this is a frequency related effect where the edges of the bars would have originally been smeared together more, and now your fancy new parts are allowing more high frequency information through and it's simply showing the edges of the bars that always there more clearly.

In the last case, my approach has been to look for a place that changing a value could potentially reduce that a little bit. Basically to create a low-pass filter in the exact spot where the jailbars are being introduced.

I haven't had a lot of success with it yet though, so YMMV. I know just enough here to understand people's suggestions, but I don't have a strong enough background in electronics to do much innovating.

Random jailbars in the raster is one of the very most difficult things to figure out.

From what I've been able to gather in my quest to solve jailbar problems in my own sets is the following:

1. They can be caused by missing shielding. Sometimes there were big metal shields covering things like the flyback or other noisy sections of the chassis, and they go missing during the life of the set
2. Sometimes grounding problems can cause them. This can also be caused by a missing ground that was completed by a shield or a poor connection on the tube itself or elsewhere.
3. In many cases, the jailbars were always there, and the reason you are seeing them is because newer components are somehow accentuating their visibility. I have been told by people more experienced than me that this can be due to fast, better performing parts passing through more of the bars. I would assume that this is a frequency related effect where the edges of the bars would have originally been smeared together more, and now your fancy new parts are allowing more high frequency information through and it's simply showing the edges of the bars that always there more clearly.

In the last case, my approach has been to look for a place that changing a value could potentially reduce that a little bit. Basically to create a low-pass filter in the exact spot where the jailbars are being introduced.

I haven't had a lot of success with it yet though, so YMMV. I know just enough here to understand people's suggestions, but I don't have a strong enough background in electronics to do much innovating.

I don't know if my way of thinking about it is correct, but I feel that if none of the changes have even affected the bars, it must be somewhere else. I've changed every diode, the related ceramic capacitors and resistors. I changed the damper diode. Rerouted harnesses. Cleaned contacts. Checked all ground points on terminal strips. Replaced every electrolytic with part numbers from SM. Checked IF cables for damage and proper grounding. Not once have I seen any change in the jailbars. The only sections I haven't dealt with is the flyback, IF and yoke. The only missing shield is from the subcarrier module and that's due to the new module not needing it as it has its own shielding.

I found an NOS IF module that is bright and shiny and the box doesn't say "remanufactured" on it. The only thing I don't know is if the module comes pre-aligned. If not, then I'm short on equipment to do so. I also found an NOS flyback. I can easily test the IF module, but the flyback isn't plug and play.

I am dedicated to getting this TV back to as new a condition as I can and have been happy with all the work I've done that has increased the image quality and audio, but the jailbars are way too noticeable. They cover the entire screen, albeit less as they go from left to right, but they're still there.

I think the new IF module would be prealigned. Stop agonizing and just try it.

It's not likely it would affect the jailbars, but who knows? Replacing it might fix a ground problem.

I don't know if my way of thinking about it is correct, but I feel that if none of the changes have even affected the bars, it must be somewhere else.

Yeah, it's extremely tricky.

I still think that it's probably a case that the set always had those bars, but there was something acting as a low pass filter which provided some kind of anti-aliasing just as a side-effect of the component tolerances at the time.

Or it's a shielding problem or a grounding problem.

Yeah, it's extremely tricky.

I still think that it's probably a case that the set always had those bars, but there was something acting as a low pass filter which provided some kind of anti-aliasing just as a side-effect of the component tolerances at the time.

Or it's a shielding problem or a grounding problem.

I think I'm finally going to find out if it's an IF issue. I watched a video on someone taking a portable set from '76 and connecting composite directly. He had to short a resistor in the IF section, but I won't need to do that as the entire IF module comes out on mine. Also, the point where he inserted the composite he use a 75ohm resistor and a 47uf capacitor. I am going to modify an old 75ohm RCA by cutting off the head and attaching the resistor and capacitor and terminating it with a barrel connector big enough to fit over the C1 test point to insert directly into the video amp like the IF does. If it works, I'll not only have the video image, but I'll be able to see if the bars go are gone or not. Even if they are still there, I'm going to create a way to leave the IF in and switch from RF to Composite as needed.

Okay, so on the remote motor setup, I think I know what's what. The motor's setup is spring loaded and puts pressure on the tan gear thing. The other end side of that gear connects to a gear in the channel selector unit and that gear has metal contacts that also act as sprints pushing from the other side towards the motor. The tan gear thing doesn't actually mate up perfectly with the black one. The teeth only match up around 1/3 of the circumference. It is designed to slip over the black one when the motor turns, but stay in place all other times. With pressure from the spring on the motor side and the channel selector side, it's enough to let the tan one turn and then turn the channel selector gear. Still would like to get my hands on a replacement for possible future need.

Once I've gotten the replacement caps delivered, I'll install and reassemble. Hopefully the cleaning and reassembling will cure the channel changing issue.

I think the new IF module would be prealigned. Stop agonizing and just try it.

It's not likely it would affect the jailbars, but who knows? Replacing it might fix a ground problem.

IF module arrives today. Will have to wait til I get the caps replaced in the tuner control center board and put the unit back in the set. I'll swap the IF module after I verify I got everything back and working.

I got the NOS flyback, but I'm questioning the instructions with it. I am not planning on installing it and if I do, it's only as a last resort. The one installed in the set is S96453-01. The replacement is -02. The sheet sent with it says that if replacing a -01, I need to remove the .0006 2KV ceramic before installing. I've compared each unit and other than the new one having the safety caps already updated, and a single resistor replacing 2 in parallel on the current one, I see no real difference. If the current one has the 2KV, and all other components on the new one are the same connections and values, why remove the capacitor?

Thing is, if it does need removal, then I have one to test in the circuits that use this capacitor (damper, boost, etc.). Haven't been able to find this value in 2KV.

While removing capacitors from tuner control board, the solder sucker not only took the solder, but the pad as well. These are the worst pads I've seen. Since I have no idea how to restore the pad, if even possible, I am thinking of soldering the lead to the next joint on the trace. Just want to make sure this is okay before I do it. Pic attached.

Also, removing the board meant two gears falling out. I figured out their alignment, but hope it all goes well as the only way to know is reinstalling for testing. Wonder why this part of the tuner isn't in the Sams supplemental along with the remote board that is part of this assembly.

I retested the CRT with a BK 470. It passed all tests. When setting the cut-off, all three guns were close in knob position to set it. The emissions test showed the green gun lower than the red and blue, but not by much. The instructions don't say anything more than the CRT is considered good as long as each gun is in the "Good" section. The scale goes up to 20 and the red and blue were 13, while the green was 12.5. I'm assuming those are good reading for a 52 yr old tube and it has many hours left. Each gun passed tracking as well.

Hopping over the adjacent trace would be acceptable in this application. I would suggest using a short piece of spaghetti tubing to insulate the lead over the hop. You might also consider potting the electrolytic in a very small amount of adhesive to give it some mechanical stability. You could also gently scrape off the enamel on a small area at the end of the remaining trace to create a new pad. Form the lead to recreate the path of the missing trace, and solder to the pad you created. Consider potting the lead in a very small amount of adhesive for stability. This capacitor is in a sheltered area, so not as likely to be disturbed.

Out of curiousity, were the old caps bad?

You could also post a WTB for the entire board and/or workable 25EC58 chassis.

The 25EC58 was not rare. I am seeing 2 on FB MP in the midwest, both working, one is a non-remote Avanti. You are very dedicated to this TV, having a good working baseline chassis could be a great advantage....

I would consider the flyback a last last resort on the jail bars.

Do you have a spare HV tripler?

I'm not familiar with the BK 470, someone who is will have to comment on your CRT test. From the pictures you have posted it appears you have the brightness on the low side, in a darkened room, good focus and gray scale. It would be interesting to see how it looks with the brightness up a little bit.

Hopping over the adjacent trace would be acceptable in this application. I would suggest using a short piece of spaghetti tubing to insulate the lead over the hop. You might also consider potting the electrolytic in a very small amount of adhesive to give it some mechanical stability. You could also gently scrape off the enamel on a small area at the end of the remaining trace to create a new pad. Form the lead to recreate the path of the missing trace, and solder to the pad you created. Consider potting the lead in a very small amount of adhesive for stability. This capacitor is in a sheltered area, so not as likely to be disturbed.

Out of curiousity, were the old caps bad?

You could also post a WTB for the entire board and/or workable 25EC58 chassis.

The 25EC58 was not rare. I am seeing 2 on FB MP in the midwest, both working, one is a non-remote Avanti. You are very dedicated to this TV, having a good working baseline chassis could be a great advantage....

I would consider the flyback a last last resort on the jail bars.

Do you have a spare HV tripler?

I'm not familiar with the BK 470, someone who is will have to comment on your CRT test. From the pictures you have posted it appears you have the brightness on the low side, in a darkened room, good focus and gray scale. It would be interesting to see how it looks with the brightness up a little bit.

The traces on this board are very fragile it seems, so I would be hesitant in scraping off anything to expose more. I will go the route of attaching to the other lead and using some of the tubing I have to cover the exposed lead. I have a glue gun, but am not sure if hot glue is acidic in the long term.

From that board, there is a 1uf that is 123% out of spec. It is showing as 2.23uf. There is a 50uf that is connected to the AFC to ground that is 26% out. It shows as 63uf. The rest are just under 20%. As for a replacement board, I found an NOS, but will get that as a last resort.

I'd like to keep the set as original as possible, so don't really want to swap in another chassis. If all my work doesn't rid me of the jailbars, I will live with it and possibly tackle it again in the future when I have more knowledge.

I don't have a spare OEM tripler, but I do have the NTE replacement that I got for possible future need. The set has the original tripler and the only thing I needed to change with the focus divider.

It's going to be interesting getting the assembly back together. I need to line up two gears so their wipers touch the proper pads on the boards. If they get out of alignment, the wrong light will illuminate with the wrong channel. Either from the factory or afterwards, there is a red mark on one gear and a black on the other. If you line them up, they are properly aligned. However, you now need to place the board on top of them without disturbing that alignment. What makes it difficult is the wipers are such that they act as springs, so the gears aren't sitting flush until the board is placed on top of them to seat them. See attached.

While frustrating at times, I am enjoying the challenge and gathering knowledge along the way. I am quite attached to this set as I've always wanted one since the first time I saw one. I have one now and I'm dedicated in restoring and preserving it for the future.

Not my best work, but it should hold. Checked continuity to surrounding components and all is well.

Also, guess Zenith thought of everything, but not having the SM for this assembly, I stumbled across it by accident. The issue with lining up the gears and making sure they were still aligned after assembly seemed an impossible task, but it seems there is a small hole in the board, right above the point where the two gears mesh and it is used to verify the red and black are correct. I used my video microscope over the hole with a bright light and could see the black tooth of one gear between the two red teeth of the other gear. Hard to see colors in pic, but they are there.

Success on the tuner! All caps replaced, reassembled with gears properly aligned and cleaned up. After installing it back in the set, all tests went perfectly. It no longer hesitates, fails to move to next channel and the AFC is working again. I know I got the gears aligned correctly as the channel lit matches the corresponding tuning knob. :lmao:

So now my next task is to remove the IF module and connect a composite signal directly to C1 using the cable I made with a 75ohm resistor and 47uf capacitor. I have a sacrificial DVD player that volunteered to make the connection.

While I had the scope out to check the signal on C1, I figured I'd check other waveforms in that area. I checked the base of the ABL (Automatic Brightness Limiter) and I got the waveform that in the past made me think it was the reason for my jailbars, but was told by others here it was okay. Comparing what I get to the low definition waveform in the SM, I still think mine is not right. I have the peaks like in the example, but between them is a long flat line in the example where mine has ripples from tall to short along that line. If that's the way it should look, wouldn't the example show it? I'm attaching an image.

More on the ringing seen on the brightness limiter circuit. I have looked over recent pics of the chassis underside after studying the schematic. There is a 7w resistor that comes off the tripler that connects to the flyback connection where a black wire goes under the chassis. Where it connects is a 7.5V Zener diode noted as a power regulator. From there a wire travels along front side of the chassis and connects to the brightness limiter pot. I can see in a recent pic that I never changed that diode. In the attached pic you can see it and the leads seem discolored from heat. Again, my limited knowledge in circuits had got me again. Still, I believe this setup is designed for power to flow and be limited to 7.5V by the diode, right? If that diode is failing, or out of spec, can that cause the ringing? I have 2 new diodes from Zenith, but they don't look like the current one. These are glass and smaller. The color bands on them give me 194 and that matches the SM part number of 103-194.

So I think it's time to change that diode. No point testing it as to do so requires it coming out, a bench power supply and DMM. Might as well just put the new one in and save some time. While I'm at it I'll replace the setup switch as well.

Can someone help me interpret this adjustment from the SM?

I think the reason the new IF module didn't work right was due to the detector level not being set properly. While all other parts the IF can be aligned outside of the set at the factory, the detector level might be set dependent. The SM has the procedure and I'm sure the first part of it is just to setup for the main alignment in the section below this one, so isn't necessary for this procedure.

I'm attaching the procedure. What it doesn't note is whether the set needs to be on or off. I'm assuming off and I need to connect my power supply, set to noted voltage and make adjustment while measuring with DMM. Is this correct? If the set is on, won't my injected voltage be thrown off by the voltage provided to the IF?

So I have a question about brightness control and where it should start affecting the brightness. I never paid much attention to it, but today I decided to follow "proper" adjustment of contrast and brightness. Brightness is supposed to be first and you bring it up to bring out detail in dark areas, but not so much that they turn grey. Then you adjust contrast to bring up the overall brightness of the image. When I turned both controls down, I started to up the brightness, but noticed there was no affect until about 2/3 of the rotation range or so before it started to show. I thought it might be because I had the contrast down too low, so I set that to about center. Still, the brightness didn't start kicking in until around the 2/3 rotation.

Is this correct? I have no knowledge of being able to set the brightness range on this set and the SM has not info, either. All I can set is the brightness limiter. If the control should have more of a range, then maybe I have an issue somewhere in that circuit.

The brightness control may have a wide range just to accommodate circuit tolerances - as long as you can reach the correct setting without being near one end or the other of travel, it should be OK.

The brightness control may have a wide range just to accommodate circuit tolerances - as long as you can reach the correct setting without being near one end or the other of travel, it should be OK.

Over brightness is achieved just before end of travel.

Some success, and a setback.....

I tested all CRT voltages and they are pretty much what the SM has. I then ditched the pattern instructions for contrast and brightness and started with brightness til blacks started turning grey and back off til black again. Then adjusted contrast to bring up overall brightness and went back an forth between them to fine tune. From there I use a blue colored filter to do color and tint. Used another test pattern to adjust peak picture till all ringing was gone, but not over softened. From there I brought up the geometry patter and adjusted vertical linearity. After all was settled, see attached pic 1 and 2 for results.

Now look at pic 3. While viewing, I completely lost horizontal sync. No adjustment of the control would bring it back. I then removed the board and reseated which gave me back sync, but the image is still unstable as it is wavering every few seconds like it's about to lose sync again. The SM says it's either horizontal phase detect, oscillator or AFC. Each one of those is a socketed transistor and they were recently installed to put correct PNs on the board. Maybe one is failing? More likely they need to be tested and then soldered in place.

Pic 4 is a bonus. :lmao:

When you have a symptom coming and going, it is not a failed transistor.

Tap, press and wiggle things to look for an intermittent connection.

When you have a symptom coming and going, it is not a failed transistor.

Tap, press and wiggle things to look for an intermittent connection.

Could it be the transistors in those little metal sockets? I've had the set running for more than an hour now and it stopped wiggling like it was about to lose sync. I wish I could remember better, but when I first got the set it had horizontal sync issue, so I put in a new board. It didn't work and I wound up swapping the oscillator transistor from the old board and it worked. Put the other one back and it stopped working. So the current board has the original transistor. Maybe I should look for a new transistor. I'll see if I can find the one that was on the new board and test it. I have a box of old parts, so I think I still have it. Been 13 years and the brain isn't serving up memories like it use to.

The picture looks like a typical Zenith; sharp, with great color!

The picture looks like a typical Zenith; sharp, with great color!

Now if I can only get the horizontal sych working again. :lmao:

I think I found the horizontal sync issue, maybe. The 755 horizontal driver transistor tests good as far as not being shorted, etc. However, the hFE is zero. According to the specs of the ECG157, it's replacement, it should have a minimum hFE of 30.

Ordered an OEM replacement.

I just reread the IF detector output adjustment again. I waited for someone to chime in, but I'm just going ahead and do it. I realize now the set needs to be on while doing this as the voltage I'll be inserting is 7.2V and I'm adjusting for an output of 8.5V. Not an electronics wizard, but I don't think that is possible without the set's power supply having a hand in it.

The insertion point is on the line going between the AGC connections of the IF and Video Processing Modules. SM says normal voltage of the AGC is 5.79 to 7.51V. The voltage being measured while adjusting is on C1 (detector output).

Not sure, but to be on the safe side, I might put a capacitor on my positive lead of the power supply to keep any DC from heading up my way.

Wish me luck.

You do not need or want a capacitor in the external power supply lead. That would defeat the insertion of 7.2 volts. The 7.2 volts is to force a known AGC voltage in the system when making the adjustment of the output.

I think I found the horizontal sync issue, maybe. The 755 horizontal driver transistor tests good as far as not being shorted, etc. However, the hFE is zero. According to the specs of the ECG157, it's replacement, it should have a minimum hFE of 30.

Ordered an OEM replacement.
You must not be measuring hFE correctly. A transistor cannot test good with a hFE of zero.

If the driver transistor were dead, you likely would not have horizontal scan at all. The driver transistor is very unlikely to be the cause of intermittent sync.

Again, if some function is intermittent, you should applied mechanical tapping, pressing and jiggling to find an intermittent connection.

You must not be measuring hFE correctly. A transistor cannot test good with a hFE of zero.

If the driver transistor were dead, you likely would not have horizontal scan at all. The driver transistor is very unlikely to be the cause of intermittent sync.

Again, if some function is intermittent, you should applied mechanical tapping, pressing and jiggling to find an intermittent connection.

I double and triple checked with two different meters and both read zero. I also found my old horizontal board and pulled the 755 off and tested. it had an hFE of 82.

I've tapped the crap out of everything, but nothing changed. I pulled all boards and reseated, nothing. I took the horizontal, vertical and chroma boards out and checked all the resistors and transistors. I then remembered the video processor board. It gets the sync signals. I check the resistors and all but two are within the noted value. The others were so far out, I'm going to lift a leg for better testing. One is 4.8K out of 10K and the other is 6.8K out of 18K. But most concerning is the IC. The legs are black from some kind of corrosion and/or heat. I tried cleaning them, but it won't come off. It is has migrated down many of the legs. There a couple with bluing from heat.

I've uploaded a video of the problem. Maybe a visual will help. I really don't know where to look as there are multiple places the horizontal sync is processed (IF, video processor module and horizontal module). As suggested I have tapped on everything, wiggled all connections, removed and reseated modules and tested a number of components on the modules.

It no longer seems to be intermittent sync as I have not been able to get it back, even for a moment. Been working on it for about 7 hrs now.

I've ruled out the IF module. See attached pic. It is from test point C1, Detector Output. I see the section where blanking, color burst and horizontal sync take place, followed by the video information.

https://youtu.be/Ftj62sprzNY

The horizontal is running way off frequency. If the horizontal hold adjustment is a coil you might be able to bring it back in with that.

+1 Horiz osc is way off frequency. This is almost entirely contained on 9-57 Horiz Board, with the exception of the horiz osc coil/hold control and the attached capacitor that forms the circuit that determines the osc frequency.

+1 on the Q803 121-755 Horiz Driver transistor not being the cause. ECG 190 is a closer substitute.

The question is, can the osc run on frequency or is the AFC driving it off frequency.

Do you have a spare 9-57 Board?
Is the plastic stop still in place on the horiz hold control? Has it already been forced past the stop?
Have you replaced any other components on the 9-57 Board?
Re-examine and tighten pins and connectors A11, U4, T13, that connect to the coil.

Common problems:

R808 330ohm 1/2w replace and upgrade to 1w
R821 2.2k 1w replace and upgrade to 2w

Lead sockets for the transistors are always problematic, most people will either remove the pins and solder the xsistor directly to the board, or solder the leads in the pins. Every rebuilt board I've ever seen, Zenith or PTS, soldered the leads into the sockets.

From there you need to troubleshoot the board. At least its not intermittant anymore?

On the Video Proc IC, I've had luck gently scraping with an Exacto knife, also taking a small piece of green scotchbright soaked in DeoxIT or CRC Cleaner, held with a needlenose and gently scrubing. Be care not to over manipulate the pins.

+1 Horiz osc is way off frequency. This is almost entirely contained on 9-57 Horiz Board, with the exception of the horiz osc coil/hold control and the attached capacitor that forms the circuit that determines the osc frequency.

+1 on the Q803 121-755 Horiz Driver transistor not being the cause. ECG 190 is a closer substitute.

The question is, can the osc run on frequency or is the AFC driving it off frequency.

Do you have a spare 9-57 Board?
Is the plastic stop still in place on the horiz hold control? Has it already been forced past the stop?
Have you replaced any other components on the 9-57 Board?
Re-examine and tighten pins and connectors A11, U4, T13, that connect to the coil.

Common problems:

R808 330ohm 1/2w replace and upgrade to 1w
R821 2.2k 1w replace and upgrade to 2w

Lead sockets for the transistors are always problematic, most people will either remove the pins and solder the xsistor directly to the board, or solder the leads in the pins. Every rebuilt board I've ever seen, Zenith or PTS, soldered the leads into the sockets.

From there you need to troubleshoot the board. At least its not intermittant anymore?

On the Video Proc IC, I've had luck gently scraping with an Exacto knife, also taking a small piece of green scotchbright soaked in DeoxIT or CRC Cleaner, held with a needlenose and gently scrubing. Be care not to over manipulate the pins.

The horizontal hold still has the stop on it and it hasn't been turned past it. The image does show slight change as I rotate the control.

I replaced the 755 on the current board yesterday, no change, so I have to agree, it's not the issue.

I have replaced all the transistors on the board in the past month, other than that, it is unchanged. Could a bad transistor in another part of the board cause it to loose synch? If so, I have all the original transistors. Maybe one of the new transistors is bad. I also have the original 9-57 board, but after 13 years I can't remember why I had to replace it. Guess I could swap it and see what happens.

The lead sockets on the current module have one crimped socket per transistor. I guess they did that to make sure they were secured.

I tested the resistors. R808 is 310 ohm and R821 is 2.4K ohm.

I was given a "new" video processor board years ago, but it never worked. Then I noticed the top corner of it had a red mark on it. I'm betting it was the bad one put back in the box and that mark was to let them know that. Somehow it got out. Never got around to finding out what was wrong with it, but I remember the board yesterday and took the IC out of it and put it in the existing board. Problems solved for that one.

Okay, I'm going to put the old horizontal in right now and I'll post my results. I'll also retest the transistors I put on the current board and see if any have gone bad.

Well now I know why I replaced the 57 module. When installed, there is no image or raster on the screen, but there is sound. I hear the buzz of HV, but the CRT is not active.

Okay, I think I know what happed to the old 57 module. See attached pic. Back when I first got the set, I was told to check all the transistors to make sure they are seated. I guess I pushed too hard on this one as the emitter lead left the side opening of the socket and joined up with the base socket. I'm no expert, but I think they call that a short. :lmao:

I'm going to test that transistor, and possibly just replace it no matter what testing says. Then I'll reinstall the board and test again.

Okay, fixing the insertion issue with the transistor fixed it. I put the board in and it fire up. Slight adjustment of the horizontal hold and it's all good. I'm going to let it run for a few hours to make sure it has been fixed. Now to use the removed board to practice my troubleshooting and repair. This board is exactly what I need for that.

Appreciate all the help. I'm sure it won't be the last time I need it, that's for sure. When this is done, I have a B&W RCA 12" from '75 and a 13" Hitachi from '82. :smoke: Not to mention a Canon Monochrome computer monitor that has a weak CRT. The socket adapter I have for my B&K had a couple wires pulled from the socket. I asked the previous owner and they said something about that socket had the wrong wiring for many of the monochrome monitors and he said someone switched a couple leads. Now I'm uncertain of using it, so I need to find the wiring diagram from B&K and compare it to the connector of the tester to make sure they all line up. Once that is done, I'm sure I'll have to go the rejuvenation route with it.

I've ruled out the tuners being the source of the jailbars. I have a modulator that outputs to UHF and tested a laserdisc and VCR on channel 82 and the jailbars are still there.

The next step is the IF module. I found out why the new IF is over saturated. I need to adjust the detector output. I'm going to just turn it down by eye at first to see if the jailbars are still there. If not, I'll do the SM adjustment procedure. If they are still there, I'll put the original back.

After that, I'm not sure I have the ability, currently, to go any further in trying to find the source. I won't stop trying, but all the while I'll enjoy watching what I've been able to accomplish so far in making the image as close to factory new as possible.

Can ringing like what is causing my jailbars come from the 240V and/or 750V boost circuits? The reason I ask is I realize the diodes have not been changed. The 750V was cut and tested, but the 240V wasn't. I have one new diode, but need to get the second.

Also, the capacitors across these are 2KV, but the diodes are only 1.4KV. Since their voltage ratings are not standard, and I haven't been able to find them, can a voltage of 1.5KV be used?

Diodes themselves cannot cause jailbars. Jailbars could be gnerated in a circuit that happens to contain the diodes, but changing the diodes would not fix them.

Are you asking about replacing the caps or the diodes?

1.5 kV diodes can be used in place of 1.4 kV diodes.

1.5 kV caps should not be used in place of 2 kV caps. The rating may or may not be important for steady state operation, plus, it could be specified to tolerate temporary overvoltage due to CRT arcs or some other condition.

Diodes themselves cannot cause jailbars. Jailbars could be gnerated in a circuit that happens to contain the diodes, but changing the diodes would not fix them.

Are you asking about replacing the caps or the diodes?

1.5 kV diodes can be used in place of 1.4 kV diodes.

1.5 kV caps should not be used in place of 2 kV caps. The rating may or may not be important for steady state operation, plus, it could be specified to tolerate temporary overvoltage due to CRT arcs or some other condition.

Just thought that if the specs of the diode(s) were out, then it might introduce noise in the circuit that appears as bars. Since I have one diode, I thought I'd replace a current one, most likely on the 240V boost, then the other one when I get its replacement.

I remember years ago when I first started looking at the jailbar issue I was told to put a capacitor of the same voltage in parallel with the B+ filter caps to see if it helped. I didn't, but was wondering if the same would apply to the caps across the boost diodes and damper diode. I have some 560pf 2KV caps an was going to see if they worked in place of the 600pf across the damper and boost diodes. But now wondering if I could parallel them to see if it has any affect on the bars. If not, I have one real 600pf 2KV on an NOS flyback that's instructions say if replacing my current unit I'm supposed to remove it. So if I ever need the new flyback, the capacitor isn't needed. But since it's only one, and my set has three, I'd like to use it where it's actually needed.

The jail bars frequency is in the 100 kHz or so range. It takes significant inductance to resonate at that frequency with the caps that are across the diodes. Take your spare cap and connect it across an existing diode cap and see if there is any difference. You don't have to remove the existing cap to see if the capacitor across the diode is having any effect on the jailbars. If you do see an effect, you have a starting point for investigating from there. If you don't see any effect on the jailbars, you can stop wasting your time and look for some other cause.

This advice is based on the caps in question being across the diodes as you describe and not from one end of the diode to somewhere else.

The jail bars frequency is in the 100 kHz or so range. It takes significant inductance to resonate at that frequency with the caps that are across the diodes. Take your spare cap and connect it across an existing diode cap and see if there is any difference. You don't have to remove the existing cap to see if the capacitor across the diode is having any effect on the jailbars. If you do see an effect, you have a starting point for investigating from there. If you don't see any effect on the jailbars, you can stop wasting your time and look for some other cause.

This advice is based on the caps in question being across the diodes as you describe and not from one end of the diode to somewhere else.

There are two that fit the criteria. The one on the damper diode and the one on the boost rectifier for the 240V.

The damper diode will have to be done from the bottom, but the boost can be done from the topside. The diode and cap for boost are across connection 13 of the terminal strip by the flyback. I can just connect the cap to those for testing.

Can I use clip-on leads to them? The damper diode is from collector to ground and the SM has the collector at 125V and the boost is 240V.

I find it interesting that the new flyback is one revision newer than current, has the same resistors, capacitors, etc..... Yet, it says when replacing my current version, I need to remove the 600pf 2KV capacitor. The capacitor on mine is on the FB side of the boost voltage to ground. Guess they figure since the supply line going to the diode has one of those capacitors across it, thing the supply side of it to ground isn't necessary?

"Guess they figure since the supply line going to the diode has one of those capacitors across it, thing the supply side of it to ground isn't necessary?"
A cap across a diode and a cap from one end to somewhere else serve different purposes. One place doesn't sub for the other. There must be something different about the flyback transformer itself to require removing the cap.

Re clip leads: keep leads short and be very careful about accidental shorts, as the diodes would not like that.

"Guess they figure since the supply line going to the diode has one of those capacitors across it, thing the supply side of it to ground isn't necessary?"
A cap across a diode and a cap from one end to somewhere else serve different purposes. One place doesn't sub for the other. There must be something different about the flyback transformer itself to require removing the cap.

Re clip leads: keep leads short and be very careful about accidental shorts, as the diodes would not like that.

If there is something different with the flyback, I can't find it (visually). The capacitor only stays in if you're replacing the -02 with this -02. The original -00, -01 and -03 deletes the capacitor. Not going to put anymore thought into it. Just glad I now have a 2KV capacitor. If I do find that one of the current ones is not up to spec, I have a replacement.

The leads I have are 10" and rated for 600V. Clips are insulated except for the bite section.

Voltages in some parts of the horizontal section can exceed 600V, so i would play it safe.

Voltages in some parts of the horizontal section can exceed 600V, so i would play it safe.

I only plan on testing on 240V boost and the damper diode. According to the SM, the collector on the HOT is 125V. And of course no connecting/disconnecting while set is on. :nono:

Okay, curious results of parallel capacitor on 240V Boost.

I remembered I had a 560p 2KV capacitor, so I decided to use that in parallel to the 600p 2KV across the boost diode. The results were noticeable, but didn't eliminate the bars, but did reduce them. Don't know if it reduced the ringing or the overall brightness of screen. I'm assuming it hasn't done anything to eliminate the bars, just made them dimmer, which might mean an overall dimmer screen? If the original cap is in spec, then I upped it to around 1160.

Anyway, I also measured voltage. On the supply side from the flyback, it's 131V. On the other side of the diode, it's 249V. I'm assuming that is within specs for the 240V boost circuit.

I've attached a couple of pics. They look similar, but the one with cap is dimmer. I figure the bars should have changed in other ways, narrower, less of them, etc.

Tomorrow I'll try across the damper diode. Need to put the set on its side and remove the base and access panel for that.

The results were noticeable, but didn't eliminate the bars, but did reduce them.

In my experience with fighting jailbars (so far), eliminating the bars is often related to smoothing out them out. Doing so tends to make the picture a little softer in the process.

In my experience with fighting jailbars (so far), eliminating the bars is often related to smoothing out them out. Doing so tends to make the picture a little softer in the process.

After duplicating the test, I determined that it was the bright logo from the DVD player's screen saver that created the difference it bar intensity, not the capacitor. So the boost section capacitor is doing what it's supposed to be doing.

I'm about the flip the set on its side and remove the bottom and parallel the damper diode.

You wouldn't happen to know if removing the Automatic Brightness Limiter's transistor would disable the function and leave the set running without the function? The reason I ask is that of all the places I've scoped, the ringing is most visible on that circuit. I also remember last time I worked on it, just getting the scope's probe near the focus lead gave a ringing pattern. Is it possible for jailbars to come from the tripler?

Well paralleling the damper diode didn't get rid of the bars, but it did something I didn't think would happen. It reduced the overall brightness. I guess the added capacitance did that?

It's all buttoned up and proudly showing off her amazing image. Jailbars don't show up on dark scenes where I'm assuming it's below the level of black. For instance, I put on Buck Rogers TV show from '79 and all the space scenes were perfectly black. The only time the bars showed was during scenes with low light, not the absence of it.

One more part of the video chain eliminated.

The IF module is not the source of the bars. I installed the new IF and after adjusting the detector output to proper level, the bars are still there. Put back the original IF.

Next in the chain are the ABL, Blankers, 3rd Video Amp and then 4th Video Amp.

So far I've eliminated the tuners, IF, horizontal module, subcarrier module, B+, damper diode/capacitor and 240V Boost diode/capacitor. With all the electrolytics replaced with exact parts noted in SM as well. Transistors on the chassis and horizontal module have been replaced with factory correct.

There is a zener diode on the 4th video amp (emitter to collector/ground). Since this is acting as a voltage regulator, I don't think it can create the kind of noise to cause bars.

I also have checked all soldered ground points on the terminal strips to chassis, shielded cables and on the boards I've tested. I have tried a number of different routings of leads and isolated the yoke leads from all others.

If I never get rid of the bars, I'll still be very please with the overall image quality I've been able to achieve. The bars will be a very small price to pay to have an amazing set.

Best compromise between no jailbars and light jailbars. The overall level of brightness and contrast is too low when set to remove the bars. Then they are way too distracting when set to proper levels. So I have set it below where I where I normally view, but above where the bars are too distracting.

A few pics of the journey so far.

Looking at these pics on my laptop, I can't see jailbars in any of them. Have to try on the desktop monitor, I guess.

The reason I ask is that of all the places I've scoped, the ringing is most visible on that circuit. I also remember last time I worked on it, just getting the scope's probe near the focus lead gave a ringing pattern. Is it possible for jailbars to come from the tripler?

Yes. The tripler is part of the flyback circuit, which can be the source of the bars. When this journey started, I recommended shielding all of that to see if it went away. Did you ever try that?

Sometimes the bars can couple into the video just from proximity. One test I've done in the past is to make long extension leads between my flyback and the PCB and physically move the whole circuit away from the set and put it inside of a big steel can covered in thick plastic to prevent anything from shorting together. This is really the only foolproof way to eliminate proximity as a source for the bars coupling into the signal. It's dangerous though, so be very careful if you actually try it. I don't know how having an external tripler would effect the situation though. That's lots of high voltage parts to juggle, and the risk of arcing would be high

The important distinction here is that the bars can be one of two things. Either they are a function of the deflection, or they are a function of the video signal (ie they are modifying the actual video information before it gets draw by the deflection system).

The way you see the pulses on the probe is normal in a TV, and they will always be there. The problem is only when they are either coupled into the video signal, or when they are present in the deflection process during scan time. The bars will always be in the deflection during the blanking period and that is normal. Seeing those pulses on a probe is expected and doesn't tell you anything about where the bars are coming from.

Yes, it's normal that adding capacitance across the damper diode could cause a change in brightness. That was only to see if the bars went away, not a permanent fix.

Looking at these pics on my laptop, I can't see jailbars in any of them. Have to try on the desktop monitor, I guess.

They are there, but the settings I use on my camera to get decent pictures seems to diminish them at bit.

Yes. The tripler is part of the flyback circuit, which can be the source of the bars. When this journey started, I recommended shielding all of that to see if it went away. Did you ever try that?

Sometimes the bars can couple into the video just from proximity. One test I've done in the past is to make long extension leads between my flyback and the PCB and physically move the whole circuit away from the set and put it inside of a big steel can covered in thick plastic to prevent anything from shorting together. This is really the only foolproof way to eliminate proximity as a source for the bars coupling into the signal. It's dangerous though, so be very careful if you actually try it. I don't know how having an external tripler would effect the situation though. That's lots of high voltage parts to juggle, and the risk of arcing would be high

The important distinction here is that the bars can be one of two things. Either they are a function of the deflection, or they are a function of the video signal (ie they are modifying the actual video information before it gets draw by the deflection system).

The way you see the pulses on the probe is normal in a TV, and they will always be there. The problem is only when they are either coupled into the video signal, or when they are present in the deflection process during scan time. The bars will always be in the deflection during the blanking period and that is normal. Seeing those pulses on a probe is expected and doesn't tell you anything about where the bars are coming from.

Yes, it's normal that adding capacitance across the damper diode could cause a change in brightness. That was only to see if the bars went away, not a permanent fix.

I don't know if it's the way I've adjusted things, but I swear the bars have a more defined edge to them. Almost perfectly smooth and uniformed. I'll have to do more low light scenes and make sure.

I have not figured out a way to shield things without shorting something out. Unless there's a material that can be used as shielding that doesn't conduct, I just know I'll kill something. Is it safe to wrap the anode lead in foil all the way down covering the tripler? The connections on the tripler have black RTV on them, so I don't see an issue on that end.

Would ferrite magnets be of any use? I need one years ago and had to buy 20 of them. They are small and would fit up to 10 ga wire.

As for the tripler, I have an NTE replacement, but that would require ditching the divider and I'm not sure if the NTE is better used as an emergency replacement. I haven't been able to find and OEM one.

Tomorrow I will be scoping the 3rd and 4th video amps. Now I know the settings for the test points from the waveforms in the SM, but if I'm looking for something outside of that, what should I be looking for? AC? DC? Certain time/div? The reason I ask is I've noticed a couple test points that have two different waveforms and each one has a different time/div and produces different forms. I figure it safer to scope all leads on the transistors, but not sure if that's necessary.

I wouldn't go putting magnets around the place, sounds like a bad idea to me.

You can get pieces of steel and double bag them inside of ziplock freezer bags to prevent them from shorting out on anything. Good enough for a test.

The idea is to completely cover the parts that are making the oscillation you're seeing. If it's coupling into the video in that way, you should notice some difference. Might not cure it, but it would at least tell you that you're on the wrong (or right) path.

I wouldn't go putting magnets around the place, sounds like a bad idea to me.

You can get pieces of steel and double bag them inside of ziplock freezer bags to prevent them from shorting out on anything. Good enough for a test.

The idea is to completely cover the parts that are making the oscillation you're seeing. If it's coupling into the video in that way, you should notice some difference. Might not cure it, but it would at least tell you that you're on the wrong (or right) path.

What if I put several layers of foil inside freezer bags? Would that provide good/decent shielding? I have some 1 and 2 gallon bags. The 2 gallon would be large enough to wrap over the top and sides of the flyback and the 1 gallon over the tripler. I could also lay it on top of the chassis between it and the CRT.

Well I'm just about finished with all the connections this set is going to have. I do need to finish the trim on the table next to it, but my access to a brad nailer is gone, so I might just use wood glue. Also need to redo the carpet on the riser.

Oh, and I'm still confused about adjusting detector output level. I posted earlier the instructions. So I've figured out that I'm supposed to be on the highest channel without signal. I'm then supposed to connect 7.2V to E and ground, then a DMM from C1 to ground. The set is supposed to be one for this connection and adjustment and this is where I am confused. The circuit already has DC and and AC signal on it. Is me just connecting my power supply and injecting voltage all there is to it? Is the AC signal bad for my supply? What is my injecting 7.2V going to do to the DC already on it? And lastly, once this is done and I disconnect, the DC voltage on E will drop back to what it was before, so won't the adjustment I made change as well? As it stand s now, the voltage on C1 is around 7V.

Since there were untrained hands in this set before I got it, I'm checking all I can and this one is off, but not sure if the amount matters in the end.

What if I put several layers of foil inside freezer bags? Would that provide good/decent shielding? I have some 1 and 2 gallon bags. The 2 gallon would be large enough to wrap over the top and sides of the flyback and the 1 gallon over the tripler. I could also lay it on top of the chassis between it and the CRT.

It has to be pretty thick steel I think, not foil. There are calculations you can do, and if you wish to explore that, you can read up on Lenz's law and how it is contained in the equations of Faraday.

There are other kinds of metal that have been used by TV manufacturers that work better, the most well known of which is mu-metal.

What determines horizontal position in this set? I'm assuming it is something on the horizontal module as after swapping back to the original module after the failure of the upgraded module, the image is now off center horizontally. It was never centered perfectly with the newer module, but it was about 1/2 to the right. With the original module reinstalled, the image has move another 3/4 to 1" to the right. The horizontal control is all the way to the stop. If I rotate it away from the stop, the image moves more towards the right.

If a module swap is enough to mess with horizontal centering, is that because of something on the board out of spec, or the way it is interacting with the horizontal control? Really would like it at least back to where it was previously.

So, is my tripler 53 years old? Is the date code 7314? Other than part numbers and "YARO" or "VARO", the only thing that looks like it might be a date code comes out as 14th week of 1973. Does that seem correct?

I'm going to install the NTE526A in the set Friday. It's another test to find the source of the jailbars. When I replaced the focus divider years ago, the wires were long and I cut them to length. I have enough of the black to go from the new tripler to the focus connection on the flyback, but not enough of the white to reach the pot. I found some 18AWG 30KV wire in white and it should be here tomorrow. I really didn't want to cut the wires off the divider as I might end up keeping it and the tripler if the new one doesn't fix the bars. This way I have the OEM back and the NTE as a spare. If it fixes the bars, is there some kind of tests I can do on the OEM? Resistance? Diode check?

And of course a question. Is it okay to run the new tripler without RTV on the connections for testing? I want to be able to quickly swap it if it doesn't solve the bar issue. If not, is there something else less permanent I can do for testing to protect from arcing?

I got my hands on the plans to gut a 9-57 horizontal board and piggyback a 9-90 so I can use my old RCA VCR without the waving at the top of the screen. Only issue is I don't know how the B+ 125V is going to like/not like it. Since the B+ is passed module to module and the horizontal module is the last in line, does the B+ line care if it is cut at that point? With the 57 board, it goes in and out, but isn't used by anything on the board. If I gut the board so I can just use it as a base for the 90, the return path for the B+ will be severed.

About to install the new setup switch. I got the old one out and opened it after testing. Testing on the new switch showed no resistance. On the old switch, it showed resistance, mainly in the "setup" position. Upon inspection of the contact pads, I can see where the resistance is coming from.

Took plenty of pics to make sure I get the wiring on the new switch correct. Sure wish there was more play in the wires for easier install and soldering.

I've attached a pic. Can you guess which pads are for "setup"?

The tripler has a 500ohm 7W resistor that is one of the cement (sandbox) type. Since I'm replacing the tripler I figured I'd go ahead and replace the resistor as well. Finding the cement ones is not easy, so I just ordered a WW in the proper resistance and wattage that is a 1%. It also has a temp of up to 250c.

Setup switch and tripler are installed. Just need for the RTV to set and I'll reinstall chassis and test.

I don't think I did too bad with the wiring and soldering. The resistor was a bit longer than the original, so I had to set it a bit higher up with a longer lead on the tripler end. A bigger blob of RTV covered the longer lead.

Always wondered about the focus control lead. It pretty much just runs along the top of all the circuits on its way to the pot. Wondering if it's a noisy lead or not enough to interfere with other components.

Well I'm 0 for 2, but there is a side benefit for the work I did.

The tripler is in and set is running, but the bars are still there. The only plus is I'm now able to fully focus to the sharpest image without the moire effect on the sides of the screen. Some of the pics I posted show it. Image is as sharp as can be and no signs of the moire effect.

The setup switch is working just like before, so I the switch isn't the issue. Of course I didn't touch the controls as I'm quite happy with the grayscale I have and I figure with the brightness I currently have, I should have seen some kind of line flipping the switch.

So now I'm pretty much at the point where the only things I haven't replaced are the yoke and flyback. Guess it's time to just button her up and enjoy watching while learning to ignore the bars when they appear in darker scenes.

So now I'm pretty much at the point where the only things I haven't replaced are the yoke and flyback. Guess it's time to just button her up and enjoy watching while learning to ignore the bars when they appear in darker scenes.

I don't think that replacing parts will get rid of the jailbars. I don't think it would in general

The way I understand it, jailbars can end up in older TVs because the manufacturing tolerances are much better now and newer parts are so good that they show the bars. The bars were always there, but the older parts had added impedance or more efficient transistor junctions, and thus do not inhibit them.

Finding the source of jailbars, as I understand it, it usually a process of putting blocking capacitors in different places to see if they change, or placing magnetic shielding around reactive components

Perhaps I'm mistaken though. There's a lot of older, more experienced people on the forum who would have a more reliable opinion

I don't think that replacing parts will get rid of the jailbars. I don't think it would in general

The way I understand it, jailbars can end up in older TVs because the manufacturing tolerances are much better now and newer parts are so good that they show the bars. The bars were always there, but the older parts had added impedance or more efficient transistor junctions, and thus do not inhibit them.

Finding the source of jailbars, as I understand it, it usually a process of putting blocking capacitors in different places to see if they change, or placing magnetic shielding around reactive components

Perhaps I'm mistaken though. There's a lot of older, more experienced people on the forum who would have a more reliable opinion

I was hopeful, but didn't get my hopes up. I read a few sites where someone fixed their jailbars by cleaning their CRT socket and replacing the tripler. It was the same chassis as mine. Also read where someone replaced their tripler and got jailbars. They went back to original and they were gone.

For the life of me I can't remember if the set had jailbars when I first got it. I remember it was in bad shape, calibration wise and I was told that before I do anything I needed to replace all the safety caps and then the electrolytics. If the jailbars were there to begin with, they might have been masked by all the bad calibration settings.

I've been watching a youtube channel where they show the results of tantalum caps across zener diodes and uses a device to "listen" to the noise from the diode before and after. They also show using other capacitors across other diodes. Doubt that's where my issue is, but interesting learning about controlling noise in circuits. I thinking that my issue might be with a decoupling cap. I've noted a couple on the schematics that are in the boost (750V and 240V). I figure I can note the solder pot from pics and then mark their topside connection and try adding another bypass cap and note the affect, if any, on the bars.

I going to make an uneducated guess here and say the new tripler has had some impact on HV. My static convergence was off after the swap. I had to readjust it and then a small dynamic adjustment. It's back to what it was, if not slightly better.

I'm going to pause my work on this set and move on to a 13" Hitachi that I'm using as my monitor for a TI-99/4A computer. Believe it or not, but it also has jailbars on the left side of the screen. I order new capacitors and am going to test the CRT. Beyond that, it isn't worth putting money into. Following that, I have a B&W RCA from '75. It blew the fuse a few years ago, but not since. I'm assuming the old fuse was tired. I figure I'll hook it up and let it run for a while and see if it acts up.

jailbars are hard

jailbars are hard

I finally made some progress.....

I've been calibrating using the Video Essentials DVD and their pluge patterns and their instructions. This has always led to the image being dark on any other DVDs I've used, so I always adjust it. That has always led to jailbars. I decided to search for ways to adjust that differ from theirs. I think I've solved it and with decent results.

I started with contrast mid point. I then brough up brightness until the blacks were crushed and darker areas started turning grey. I then backed it off until blacks were black again. I then brought up the contrast to get a bright enough image. I'm positive this level of contrast is considered in the blooming range, but it has to be. Now all the programs I've tested show no jailbars at all. The image is very watchable, but I would like a little more light in the light areas, but to do so means bringing up the brightness and that crushes the blacks and brings up jailbars. I know it's been a while since I've adjusted and watched an old CRT television, so maybe I'm asking too much for the technology of 1974.

For testing I took my 13" Hitachi from 1981 and adjusted it the way I was the Zenith and I got faint jailbars. Readjusting the new way took them away and gave another very watchable, but not perfect, image.

So either this is a limitation of the technology, or I have an issue in the brightness/contrast circuit. Eitherway, I'm going to leave it be and enjoy it.

I'm now working on removing all the components of my 9-57 horizontal board so I can piggyback the 9-90 horizontal and be able to use a VCR without the waving at the top. I'm also hoping that the board will better center the image horizontally than the current module. It's about 1" or so more to the right than the last one that failed. Not only that, but I hope it solves another horizontal issue I'm having using the original 9-57 module. When the set it started cold, the image is messed up horizontally, but not like before when it was rolling out of sycn. It's a stationary issue and only goes away when I change channels and back, or sometimes on its own after a minute or so.

I wish I had to room for storing more stuff as there's someone near me giving away a 25EC58 chassis and same CRT as mine. Would be nice to have a spare I could use to compare or salvage for parts.

Well jailbars are gone and all out of spec parts replaced. Set is fully operational and working like a charm. Next is the touch up of paint and painting of stand.

Thanks for everyone's help. This thread is done.

Well jailbars are gone and all out of spec parts replaced. Set is fully operational and working like a charm. Next is the touch up of paint and painting of stand.

Thanks for everyone's help. This thread is done.

That's awesome. Would like to see some good photos of the finished set though!

Would be cool to see the case and also a decent close up of the video.

:thmbsp:

Which part was causing the jailbars?

This thread started getting too verbose and shotgunny and I tuned out a few pages in.

The service manual has it as video amp 4, but it's actually 3 and the set doesn't have a 4. Anyway, I replaced the 24V Zener and the .001 1KV decoupling cap on that's amp's transistor. While many said the ringing I see when I scope the ABL, and along that path, wasn't the source of the bars, it quite possibly was. I tried cleaning up the ringing from the source, but I didn't know enough to do that. The ABL's collector is sourced from the tripler. The 500ohm resistor goes to a 7.5V zener and spark gap. The Zener is on the wiper of the ABL pot which feeds the ABL transistor. I noticed that if I turned the pot, the bars changed intensity. Not much, but noticeable. I then set the ABL per SM and started tracing the circuit better. I found that the brightness, contrast, ABL, Blanker, etc. all came together and funneled into the video amp. Looking closer I noticed the zener on the transistor base and the decoupling capacitor. Didn't bother doing one than the other to see, just did both as I had them.

Anyway, while the bars are gone for standard viewing, I can still make them appear faintly if I crank the brighness and contrast beyond what is normal levels, but at the normal levels for viewing, even dark scenes, they're gone.

That's awesome. Would like to see some good photos of the finished set though!

Would be cool to see the case and also a decent close up of the video.

I still have to do some research on the cabinet paint. I am told it is lacquer and I don't think I've ever done anything with that kind of paint. I've see other's paint theirs completely, base and all, but they go with a bright white. From what I understand, the paint color used was and off white (imperial something). If I can't figure out how to touch it up and it not looking like I did, I'll repaint the entire cabinet in the original color, just won't be able to get it in lacquer.

A couple here helped me get my camera setting for taking pictures of the screen, but I don't know how to get video from my phone that is in synch with the screen. Also, I am not sure why every picture I take seems to magnify the phosphor dot patter.

Has to be a way to take a picture that accurately captures the image on screen. I took 40+ pics and these 2 were the best. I have a lower resolution Nikon SLR digital camera. I wonder if that one can be set properly for better images...???

Has to be a way to take a picture that accurately captures the image on screen. I took 40+ pics and these 2 were the best. I have a lower resolution Nikon SLR digital camera. I wonder if that one can be set properly for better images...???

Looks pretty good! The colors are definitely coming through, and I don't see any visual artifacts.

Yeah, taking pictures of a CRT can be tricky. I also will typically just take a bunch and pick the best.

I have found that the orientation of the CCD makes a huge difference though. Sometimes, if the picture is flashing too much, turning the camera 90 degrees will cure it. Sometimes it also requires that I move my camera closer or further away from the screen. Typically, I can get an acceptable picture by cycling through those two parameters (rotate camera, slowly move camera towards and away from CRT).

Looks pretty good! The colors are definitely coming through, and I don't see any visual artifacts.

Yeah, taking pictures of a CRT can be tricky. I also will typically just take a bunch and pick the best.

I have found that the orientation of the CCD makes a huge difference though. Sometimes, if the picture is flashing too much, turning the camera 90 degrees will cure it. Sometimes it also requires that I move my camera closer or further away from the screen. Typically, I can get an acceptable picture by cycling through those two parameters (rotate camera, slowly move camera towards and away from CRT).

I took so many pictures and ended up with 4 that I really liked, but still below in person visual quality. It's a bit annoying that in person I see scan lines, but not dot pattern in that line. In pics, it becomes quite noticeable with the higher resolutions. I think I'm going to wait til it's dark outside, setup a tripod, turn off all lights and try it that way. I'm sure the light behind the set is going to be picked up by the camera and it will adjust for that and might be part of my issue.

Thought I'd add something regarding the perforated cover over the swing door. I've noticed in a few pics I've seen on the internet that, like mine, many had dents in it. I had quite a few and some were pretty bad. Don't know what happened to it, but it had a rough life.

The cover is aluminum is held to the door by tabs that are left when the piece is cut to fit the door. Those tabs are bent over to hold it in place. If you carefully bend those tabs back, the mesh piece will come off. I took that piece, found the smoothest and flattest surface on which I placed the thickest piece of paper I could find to place between the surface and cover so as not to scratch it. With the cover face down, I gently tapped the dented areas with a flathead hammer until it was smooth as possible. Flipping it over often to see the progress. When it was done I put it back and bent the tabs over. I wouldn't recommend taking it off too often as the tabs will break.

The results are great. It's only under close inspection you can see it isn't perfect.

The after pic isn't the best angle, but I am too lazy to take a proper pic. Also, looking at the pic, I need to remove the transducer and clean the screen and opening.

I took so many pictures and ended up with 4 that I really liked, but still below in person visual quality. It's a bit annoying that in person I see scan lines, but not dot pattern in that line. In pics, it becomes quite noticeable with the higher resolutions. I think I'm going to wait til it's dark outside, setup a tripod, turn off all lights and try it that way. I'm sure the light behind the set is going to be picked up by the camera and it will adjust for that and might be part of my issue.

Doing it in the dark is the typical way people photograph CRTs, but beware that it exacerbates refresh rate issues. You will probably have to mess around with the distance and orientation a lot to get the right shot, and even then, choosing the best one between blanking periods to get one without the black bars in it

I found a company that can put the Bermuda Shell (is a Behr paint color) that's used on the Avante in a spray can. I have choices to make. The current paint is lacquer, so that's a no go. This paint is enamel and I have a choice of flat, satin, semi or full gloss. I know this set isn't as shiny as it once was, but I'm assuming satin or semi is a close match for sheen.

I've only seen this set new when I was a kid, so I can't remember detail about the paint other than it was white.

From my memory, the paint sheen was not too dissimilar from plastic and was what I would estimate as stain or semigloss.

Behr should be at home depot. I think you can probably go to one and get paint squares to see what the finish would be like.

I guess if I had to err on the side of caution, I'd go with the duller finish, as I don't think they were super shiny. But go with what you like.

From my memory, the paint sheen was not too dissimilar from plastic and was what I would estimate as stain or semigloss.

Behr should be at home depot. I think you can probably go to one and get paint squares to see what the finish would be like.

I guess if I had to err on the side of caution, I'd go with the duller finish, as I don't think they were super shiny. But go with what you like.

This color is one of their "archived" colors and the paint squares aren't available. I know the screen color isn't very accurate, but it is close. I always thought the cabinet was dirty, but any attempts are cleaning it didn't work as I think I was trying to clean the actual color away. I can also see where someone really tried cleaning it as there are areas on the sides of obvious scrubbing that left wear marks.

With the mix ratios they give, I think I can get a small quart of it and try it on the underside. If it's correct, I think I'll spring for the mix in an aerosol can as I think that would give a better finish than brush. I'll also do the back of the stand to see if it would look good in same color.

This color is one of their "archived" colors and the paint squares aren't available. I know the screen color isn't very accurate, but it is close. I always thought the cabinet was dirty, but any attempts are cleaning it didn't work as I think I was trying to clean the actual color away. I can also see where someone really tried cleaning it as there are areas on the sides of obvious scrubbing that left wear marks.

With the mix ratios they give, I think I can get a small quart of it and try it on the underside. If it's correct, I think I'll spring for the mix in an aerosol can as I think that would give a better finish than brush. I'll also do the back of the stand to see if it would look good in same color.

If you're spraying onto the bare plastic after sanding it down, there's a kind of primer you can get that adheres to plastic better and gives a good foundation for the top coat