Zenith 25EC58 Restoration Thread

[BeamT]

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?

[TinCanAlley]

Originally Posted by BeamT

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.

[TinCanAlley]

Originally Posted by BeamT

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.

[BeamT]

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.

[TinCanAlley]

Originally Posted by BeamT

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!

[TinCanAlley]

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.

[TinCanAlley]

Originally Posted by BeamT

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?

[BeamT]

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?

[BeamT]

Do you have the shield for the Subcarrier module?

[TinCanAlley]

Originally Posted by BeamT

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.

[TinCanAlley]

Originally Posted by BeamT

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.