I've noticed a few things that I'm not sure about. I've posted pics.

The first is the damper on the HOT. The leads look like they've encountered a decent amount of heat. The leads are no longer silver. The same goes for the zener diode in the ABL circuit. All other diodes in the set have silver leads with no signs of discoloration.

The last one is a composite resistor in the ABL circuit. I don't know if this is a defect in manufacturing or if it's heat damage. Could be someone touched it with an iron.

Thanks.

Don't know aobut the resistor. If you know the correct value, you could measure it, or just replace it as a matter of course.

If those diodes have actual silvered leads, it is normal for them to tarnish over time. Any actual heat damage would likely cause a failure, so if working, leave well enough alone.

Don't know aobut the resistor. If you know the correct value, you could measure it, or just replace it as a matter of course.

If those diodes have actual silvered leads, it is normal for them to tarnish over time. Any actual heat damage would likely cause a failure, so if working, leave well enough alone.

That's the thing. I don't know if they are good or not. With my limited knowledge, I've been able to find the ringing on the ABL. I've learned quite a bit lately from many here, but I can learn only so much via threads in a forum. That leaves me with the only thing I know, replacing components. Since I have no real training in electronics, I don't know if a zener diode in the circuit only works or doesn't work. Or if that diode could be semi-working and allowing the overshoot that is causing the ringing. I also am unsure how ringing and resistors relate or if they do at all.

I have the NOS zener and the resistors will be here on Saturday. I'm just going to replace them all and see if it helps.

You can rest assured that a damper diode either works or fails - there is no in-between. If it fails, the horizontal sweep doesn't work and you probably will blow a fuse. So, if your set is basically working and your complaint is those jail bars, it's not the damper diode. The zener, on the other hand, could fail open and the effect on operation might not be so obvious.


There are a couple of ways to check the Zener in operation. One is to measure the DC voltage across it and see if it is correct. This presumes that the Zener is conducting during normal circuit operation. But sometimes, a Zener is used in a circuit for over-voltage protection, and then it only conducts if there is a fault; in this case the voltage could be anything less than the specified value.

You can also check with a scope, but this is more complicated unless one end of the zener is grounded, because you have to check both ends and subtract one from the other to see if the voltage difference is constant and equal to the correct value.

You can rest assured that a damper diode either works or fails - there is no in-between. If it fails, the horizontal sweep doesn't work and you probably will blow a fuse. So, if your set is basically working and your complaint is those jail bars, it's not the damper diode. The zener, on the other hand, could fail open and the effect on operation might not be so obvious.


There are a couple of ways to check the Zener in operation. One is to measure the DC voltage across it and see if it is correct. This presumes that the Zener is conducting during normal circuit operation. But sometimes, a Zener is used in a circuit for over-voltage protection, and then it only conducts if there is a fault; in this case the voltage could be anything less than the specified value.

You can also check with a scope, but this is more complicated unless one end of the zener is grounded, because you have to check both ends and subtract one from the other to see if the voltage difference is constant and equal to the correct value.

This is where my lack of knowledge comes in. Take a look at the pics in this post:

http://videokarma.org/showpost.php?p=3083422&postcount=3

The schematic of the tripler with the brightness limiter and zener makes my head spin. If I'm reading it correctly, the zener is connected to the ground of the tripler and chassis ground. There's also a spark gap going across those two points. I can't seem to figure out how the zener gets its 7.5V for operation connected to two grounds. :no:

...

This is where my lack of knowledge comes in. Take a look at the pics in this post:

http://videokarma.org/showpost.php?p=3083422&postcount=3

The schematic of the tripler with the brightness limiter and zener makes my head spin. If I'm reading it correctly, the zener is connected to the ground of the tripler and chassis ground. There's also a spark gap going across those two points. I can't seem to figure out how the zener gets its 7.5V for operation connected to two grounds. :no:

The Zener is not connected to two grounds, because the spark gap is an open circuit until the voltage gets very high and causes a spark. It is there probably to protect the Zener from being killed in case of a CRT arc.

I don't know if the Zener is supposed to be always regulating at 7.5 volts, or just limiting the voltage to 7.5 volts if it tries to go higher. You can find out by measuring the voltage from the top of the Zener to ground (or scoping the top) to see if it is 7.5 volts, or if it is less.

Have you tried scoping the CRT cathodes to see if the ringing is there? This will tell you if the problem is getting in through the video chain.

I would also try placing the scope probe tip near (NOT TOUCHING) the case of the HOT to see if there is any ringing on the signal you will pick up. Try the same thing near the yoke, and yoke wires. You will need to use a low volts/div setting, but you should be able to pick up radiation of the horizontal sweep signals. Don't try to measure them directly since the high voltages pulses will damage the probe, or scope.

Your problem could be caused by the flyback, or yoke oscillating. This seems likely to me since the bars are clearly synchronized to the horizontal sweep, and you seem to be seeing it everywhere that has pulses from the flyback.

Finally, can you remember if it had the problem when you first got it (before you did anything to it). I seem to remember that you didn't mention it until you had done a lot of cap replacement.

The problem was there before the recap. I didn't mention it because I figured it might have been a bad cap. That and whoever worked on it before messed up just about everything (pincushion, convergence, greyscale, etc.). It looked like crap, yet the person selling said it worked and looked great. It really wasn't until I started cleaning it up that I realized how bad the bar actually were.

I will put on the safety cover on the probe and let the plastic rest on the HOT to see if I can get a signal. I'll do the same for yoke and yoke wires.

Now the base of the HOT get the horizontal pulse from the horizontal board. I checked all those points on the horizontal board and they matched the waveforms given. The HOT's signal on the base has to go through the horizontal transformer. I haven't scoped the base of the HOT, so maybe that should be next. Maybe there's a problem with the transformer. The SM does show a waveform for the base of the HOT. It says it should be 7V.

The Zener is not connected to two grounds, because the spark gap is an open circuit until the voltage gets very high and causes a spark. It is there probably to protect the Zener from being killed in case of a CRT arc.

I don't know if the Zener is supposed to be always regulating at 7.5 volts, or just limiting the voltage to 7.5 volts if it tries to go higher. You can find out by measuring the voltage from the top of the Zener to ground (or scoping the top) to see if it is 7.5 volts, or if it is less.

Hang in here with me. Now isn't the 500ohm 7w resistor connected to the ground of the tripler? If so, then isn't the zener connect to that (ground) AND to the chassis point (ground).

I've attached a pic of the underside. I've circled the connections in question. In the left circle is the black wire which connects to the 500ohm resistor on the tripler ground, the white/green wire to the brightness limiter pot's T1, one leg of the zener and one leg of the spark gap. The right circle is a ground point (soldered to the chassis' top side) that contains the other leg of the zener and spark gap. I'm hoping you can understand why I see nothing but grounds and no voltage for the zener.

I can't tell much from the fuzzy picture, but I suspect that the "ground" terminal of the tripler is connected to ground only through the 500 ohm resistor and series zener diode as well as the pot and 10 ohm resistor.
Even if the 500 ohm resistor were connected *directly* to ground that would not short out the diode, as there can be a voltage drop across the resistor if current is passed through it. Do an ohms law calculation and you can determine how much current is needed to raise the voltage to the zener voltage.
jr

I can't tell much from the fuzzy picture, but I suspect that the "ground" terminal of the tripler is connected to ground only through the 500 ohm resistor and series zener diode as well as the pot and 10 ohm resistor.
Even if the 500 ohm resistor were connected *directly* to ground that would not short out the diode, as there can be a voltage drop across the resistor if current is passed through it. Do an ohms law calculation and you can determine how much current is needed to raise the voltage to the zener voltage.
jr

Here's a better picture. The red outline is the ground post for the diode and spark gap. The yellow outline is from the 500ohm resistor on tripler ground connection, other lead of the diode, other lead of the spark gap and terminal one of the brightness limiter pot. The wiper of the pot goes to base of ABL transistor and terminal two of the pot goes to ground. The green outlines are the spark gap and the diode.

The reason I'm going though all this that I am not an expert in electronics and am still learning. Until I can understand how all these connections can work when they all seem to go to ground and not one of them seems to have any connection to a power source. If I can understand where the voltage for the diode and transistor bias is coming from, it will help me greatly. Is there voltage on the ground terminal of the tripler?

Is there voltage on the ground terminal of the tripler?

Must be... the designer chose a 7 watt rating for the 500 ohm resistor... that would imply that something like 0.1 amp or more (DC or average pulse) is flowing through the resistor or else the designer would have chosen a lower rated (cheaper) part. The "ground" lead of the tripler must be at least 50 volts (DC or average of higher pulses) above ground for the 7 watt rating of the resistor to make sense. Without knowing the digram of the tripler or what it is connected to, the source of the voltage is not known... but for sure the "ground" terminal of the tripler is *not* at ground potential.

jr

Must be... the designer chose a 7 watt rating for the 500 ohm resistor... that would imply that something like 0.1 amp or more (DC or average pulse) is flowing through the resistor or else the designer would have chosen a lower rated (cheaper) part. The "ground" lead of the tripler must be at least 50 volts (DC or average of higher pulses) above ground for the 7 watt rating of the resistor to make sense. Without knowing the digram of the tripler or what it is connected to, the source of the voltage is not known... but for sure the "ground" terminal of the tripler is *not* at ground potential.

jr

So I can use my DMM to test for voltage at the resistor. I am doing my best to understand how all this works. Looking at the schematics I think I might understand how the zener is working. If the voltage coming off of the tripler (though the 500ohm 7w resistor) goes above 7.5V, it opens and sends the excess to ground? Does that sound right?

So I can use my DMM to test for voltage at the resistor. I am doing my best to understand how all this works. Looking at the schematics I think I might understand how the zener is working. If the voltage coming off of the tripler (though the 500ohm 7w resistor) goes above 7.5V, it opens and sends the excess to ground? Does that sound right?

Yes, I think that you should be able to measure the voltage... it is likely a combination of DC and AC spikes, perhaps measure with both DC & AC scales. My Tek DMM 870 has a combination "AC+DC" range which is ideal, but I am not sure that many other meters have that function.

"Opens" is not the word that I would choose to describe the action of the Zener diode, it will *conduct* at its zener point and not allow the votage to rise above that point, unless its current ratings are exceeded, in which case it *will open* (burn out) and the voltage will likely go "sky high".
jr

What you called the "ground" of the tripler is not ground, it is just the low point and has some positive voltage on it due to being connected to ground through the other parts of the circuit, not directly to ground. If the Zener was connected on both ends to ground, it would indeed be doing nothing.

Have you tried scoping the CRT cathodes to see if the ringing is there? This will tell you if the problem is getting in through the video chain.

I would also try placing the scope probe tip near (NOT TOUCHING) the case of the HOT to see if there is any ringing on the signal you will pick up. Try the same thing near the yoke, and yoke wires. You will need to use a low volts/div setting, but you should be able to pick up radiation of the horizontal sweep signals. Don't try to measure them directly since the high voltages pulses will damage the probe, or scope.

Your problem could be caused by the flyback, or yoke oscillating. This seems likely to me since the bars are clearly synchronized to the horizontal sweep, and you seem to be seeing it everywhere that has pulses from the flyback.

Finally, can you remember if it had the problem when you first got it (before you did anything to it). I seem to remember that you didn't mention it until you had done a lot of cap replacement.

Okay, I scoped the HOT by placing the plastic safety tip against the shell. That's the fist pic and I see no ringing. The second pic is the focus wire and I'm assuming that's ringing on it, but I don't know if that can create the bars. Also, with the probe touching the yoke wires, I get roughly the same as the focus, but it shows less ringing the closer I get to the wires. So I'm not sure if it's really ringing or just that the probe is picking up interference.

So what would you suggest next?

If I put the probe anywhere around the flyback, I get the same as in the focus picture in the previous post. Lots of ringing. Of course I don't know if that's just because I'm not making electrical contact and just picking up on the radiating signal.

I scoped the leg of the diode that connects to the 500ohm resistor that feeds the wiper of the ABL pot, blah, blah, blah. This is what I got. It's an ugly waveform, that's for sure, but what does it mean? It was with a volts/div of .2 and a time/div of 20us.

It is really difficult to follow what is going on with the schematic incomplete and in a different thread.

Can you post a bigger chunk, so we see where the ABL signal from the pot wiper goes? Somewhere into the video amps, I assume.

Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.

Check the zener diode using the diode check on a DMM as a first go. That will conclusively check for opens/shorts. I'm betting it is still good though. Im thinking you might have a bad bypass cap in the video amp somewhere.

It is really difficult to follow what is going on with the schematic incomplete and in a different thread.

Can you post a bigger chunk, so we see where the ABL signal from the pot wiper goes? Somewhere into the video amps, I assume.

Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.

Check the zener diode using the diode check on a DMM as a first go. That will conclusively check for opens/shorts. I'm betting it is still good though. Im thinking you might have a bad bypass cap in the video amp somewhere.

The wiper goes directly to the base of the ABL transistor. From there it leaves the collector, through the contrast control and then on to the base of the base of the third video amp.

I'll do the B+ tomorrow. The DMM will tell me if the diode is working as far as passing in one direction. Wouldn't I need to supply 7.5V to open for testing in the other direction? Would a 9V battery do the trick?

Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.

Okay, here's the B+. The DMM has it at 129.8V and the waveform is attached. It doesn't look clean at all. Not sure why there are two on the scope. Scope had the 10x probe, volts/div of 1 and the time/div of 10us.

Okay, I just scoped the B+ at the test point which gets it directly from the source and something odd is happening to the waveform. Hopefully someone here has the answer.

Take a look at the two attached pics. The first one is the rippled wave form with a thin trace line. Then take a look at pic two. The line is starting thin and spreading out, then back, then out, etc. It takes about 4 to 5 seconds for the process and it keeps repeating.

So what would cause this?

What you called the "ground" of the tripler is not ground, it is just the low point and has some positive voltage on it due to being connected to ground through the other parts of the circuit, not directly to ground. If the Zener was connected on both ends to ground, it would indeed be doing nothing.
I think TCA is taking tripler ground to mean GROUND and of course its not.

OK TCA the "ground" on the tripler is grounded in SOME sets.
On those the ABL will usually be taken at R356, the "low" end of the
FBT HV winding.
Think of yours as the low side of the tripler.
R362 & R359 will have the HV current through them, the brighter
the pix the more current so more voltage across the resistors.
The Zener diode will keep the voltage at its cathode at
7.5 V or less.
Under 7.5V the zener does nothing.
Result is the ABL control will adj. between apx 0 V & 7.5 V
If a dark pix it will adj. between 0 & < 7.5 V & send that to the
ABL transistor.

Hope that helps

73 Zeno:smoke:

I think TCA is taking tripler ground to mean GROUND and of course its not.

OK TCA the "ground" on the tripler is grounded in SOME sets.
On those the ABL will usually be taken at R356, the "low" end of the
FBT HV winding.
Think of yours as the low side of the tripler.
R362 & R359 will have the HV current through them, the brighter
the pix the more current so more voltage across the resistors.
The Zener diode will keep the voltage at its cathode at
7.5 V or less.
Under 7.5V the zener does nothing.
Result is the ABL control will adj. between apx 0 V & 7.5 V
If a dark pix it will adj. between 0 & < 7.5 V & send that to the
ABL transistor.

Hope that helps

73 Zeno:smoke:

Makes perfect sense. I will file it away in my memory and hope what I've learned will help with the next lesson. :)

Okay, here's the B+. The DMM has it at 129.8V and the waveform is attached. It doesn't look clean at all. Not sure why there are two on the scope. Scope had the 10x probe, volts/div of 1 and the time/div of 10us.
Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno:smoke:

Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno:smoke:

It is the B+ directly off of the transformer and the pin is noted on the topside by a tag that says "B+".

So I should be locating the 240V B+? I'll see if I can locate it on the schematics.

Oh, and C270 was changed during the initial recap when I got the set.

Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno:smoke:

Here's the B+ 240V that feeds the video outputs. Again, I don't know why I sometimes get two traces. I don't have a reference waveform to compare it to, but it does seem that there is ringing in it.

Here's the B+ 240V that feeds the video outputs. Again, I don't know why I sometimes get two traces. I don't have a reference waveform to compare it to, but it does seem that there is ringing in it.

There is no way to tell if this is significant if you don't tell us the volts/division setting of your scope so we know what the peak-to-peak value of this waveform is.

Edit: I see you did tell the settings on a previous waveform. I suggest you check the filter cap as suggested by Zeno.

What is the amplitude of that ringing on the 240V line? What is the DC voltage?

Can you try temporarily bridging another cap between 240V line and ground to see if it improves the bars or cuts the amplitude of that ringing?

Post the section of the schematic that shows C270 and this supply for those of without a Sams handy...

There is no way to tell if this is significant if you don't tell us the volts/division setting of your scope so we know what the peak-to-peak value of this waveform is.

Edit: I see you did tell the settings on a previous waveform. I suggest you check the filter cap as suggested by Zeno.

It had the 10x probe on volts/div of 5 and time/div of 20.

I'll double check the cap. I is new and tested good w/in spec when I tested it before install.

What is the amplitude of that ringing on the 240V line? What is the DC voltage?

Can you try temporarily bridging another cap between 240V line and ground to see if it improves the bars or cuts the amplitude of that ringing?

Post the section of the schematic that shows C270 and this supply for those of without a Sams handy...

You'll have to forgive my lack of knowledge. I'm learning how to use the scope as I go along. All I can tell you is it was 5 volts/div with 10x probe and 20us time/div. How can I get the amplitude of the ringing? Do I increase decrease the volts/div and use the vertical scale just on the ringing portion?

As for the cap, I know I need one over 240V, but is there a particular value I should use? Also, should I parallel it with the current one or can I just find a 240V source and put the cap on it to ground?

I've attached the section of the schematics with the C270 a 10uf 300V. The T207 is the Flyback.

The waveform looks to be about 1.5 divisions peak to peak, so that could be either 7.5V or 75V, depending on whether or not the "5V/div" is taking the 10:1 probe into consideration.

75 vpp ripple on a 240V supply is a problem. 7.5V, not so much.

The doubled waveforms might be caused by improper triggering. Make sure you are triggering on whatever channel the probe is connected to, and if your scope has a TVH trigger mode, use it. Try rocking the trigger level back and forth around zero, and see if that makes the trace clearer.

I would start with the same value cap as you already have installed, and putting it right in parallel should be fine if it actually goes to ground. The attachment isn't showing up for me...

The waveform looks to be about 1.5 divisions peak to peak, so that could be either 7.5V or 75V, depending on whether or not the "5V/div" is taking the 10:1 probe into consideration.

75 vpp ripple on a 240V supply is a problem. 7.5V, not so much.

The doubled waveforms might be caused by improper triggering. Make sure you are triggering on whatever channel the probe is connected to, and if your scope has a TVH trigger mode, use it. Try rocking the trigger level back and forth around zero, and see if that makes the trace clearer.

I would start with the same value cap as you already have installed, and putting it right in parallel should be fine if it actually goes to ground. The attachment isn't showing up for me...

The probe was in the 10x mode. Also, the triggering is from a Leader LCG-396 Pattern Generator.

The cap is connected the following way. There's a lead from the flyback to a leg of a diode, the other leg of the diode connects to a leg of a 150 ohm 2W, the other leg of the resistor goes to the positive side of the cap and a lead that connects the 240V around the chassis and finally the cap goes to ground.

I'll have to find a local source for a 10uf 300V cap. The local Radio Shack doesn't have them in-store. Must be a place around here somewhere. Not looking forward to paying 7 bucks for shipping of a single cap.

Got any dud CFL bulbs? They usually have a 10uF 250-450V cap in the base...Though not exactly as likely to be good as a new cap.

The probe was in the 10x mode.

But some scopes can automatically detect the probe setting, and adjust the vertical scale range to reflect the probe attenuation and prevent confusion. This requires both a scope and a probe that support this feature. Do yours?

If your scope is doing this, then the scale really is 5 volts/division. If your scope or your probe doesn't do this for you, then the scale is actually 50 volts/division. This makes all the difference in the world when trying to interpret the waveforms as ripple on a power supply rail.

But some scopes can automatically detect the probe setting, and adjust the vertical scale range to reflect the probe attenuation and prevent confusion. This requires both a scope and a probe that support this feature. Do yours?

If your scope is doing this, then the scale really is 5 volts/division. If your scope or your probe doesn't do this for you, then the scale is actually 50 volts/division. This makes all the difference in the world when trying to interpret the waveforms as ripple on a power supply rail.

I have a Tektronix 465M. No auto settings for the probe.

I've been thinking about the waveform. It's a 240V source, so the 5V/Div would be too low to show it and the 10x probe would make it 50V/Div and it would cover almost 5 divisions. What I got was way under that. I'm going to use the DMM to go all the way back to the boost diode and when I find the point it's 240V, I'm going to scope it. With a setting of 5V/Div and the probe in 10x, I should get a form that covers over 4 divisions, right?

Got any dud CFL bulbs? They usually have a 10uF 250-450V cap in the base...Though not exactly as likely to be good as a new cap.

Thanks for the heads up. I have a crap load of new 26 and 13 watt CFLs from China and I don't mind gutting one or two. I'll let you know what I find.

I have a Tektronix 465M. No auto settings for the probe.

I've been thinking about the waveform. It's a 240V source, so the 5V/Div would be too low to show it and the 10x probe would make it 50V/Div and it would cover almost 5 divisions. What I got was way under that. I'm going to use the DMM to go all the way back to the boost diode and when I find the point it's 240V, I'm going to scope it. With a setting of 5V/Div and the probe in 10x, I should get a form that covers over 4 divisions, right?

Where is your baseline set? Are you operating the scope AC or DC coupled?

Typically, for checking ripple on a power supply, you would operate AC coupled, so you only see the AC component of the signal, and ignore the DC. If you are running DC coupled, the baseline should rise a bit less than 5 divisions (250V) from zero, with ripple superimposed on it. You can do a quick sanity check with a DMM, by measuring the 240V supply twice, both in DCV range (should show ~240V), and in ACV (should show close to zero if no significant ripple is present).

From what you are telling us (5 V/div with a 10:1 probe and no auto priobe ranging), the scope is actually showing you 50V per division, or a waveform of ~75 Vpp. This is WAY too much noise on a supply rail, and would easily explain the jailbars.

You really need to learn how to use a scope effectively in order to get useful information from it. Take a couple hours and watch this GREAT YouTube training session:

http://www.youtube.com/watch?v=8ZKMrzTGxLQ

Where is your baseline set? Are you operating the scope AC or DC coupled?

Typically, for checking ripple on a power supply, you would operate AC coupled, so you only see the AC component of the signal, and ignore the DC. If you are running DC coupled, the baseline should rise a bit less than 5 divisions (250V) from zero, with ripple superimposed on it. You can do a quick sanity check with a DMM, by measuring the 240V supply twice, both in DCV range (should show ~240V), and in ACV (should show close to zero if no significant ripple is present).

From what you are telling us (5 V/div with a 10:1 probe and no auto priobe ranging), the scope is actually showing you 50V per division, or a waveform of ~75 Vpp. This is WAY too much noise on a supply rail, and would easily explain the jailbars.

You really need to learn how to use a scope effectively in order to get useful information from it. Take a couple hours and watch this GREAT YouTube training session:

http://www.youtube.com/watch?v=8ZKMrzTGxLQ

Gonna get some popcorn and watch that video.

Okay, just did a scope of the 240V line just after it comes off of the resistor into the main feed (where the capacitor is and the where the 240V gets distributed). I had the scope set to AC coupling, V/D set at .5, the T/D set to 20us and probe at 1x. The rippled waveform covered 1.75 divisions peak to peak. So that would make the AC less than a volt, correct?

.5 V/div and a 10:1 probe is 5 V/div. A signal 1.75 divisions high would be 1.75 x 5, or 8.75 Vpp.

.5 V/div and a 10:1 probe is 5 V/div. A signal 1.75 divisions high would be 1.75 x 5, or 8.75 Vpp.

Sorry, forgot to mention it was in 1x setting on the probe.

...

It's best to keep the probe in X10 mode unless you're looking at very low level signals. A x10 probe provides a higher input impedance 10M, instead of 1M), so it won't load down the signal as much. It also provides some over voltage protection to the scope since there is a 9 meg resistor in series with the signal. If you forget it's in X1 mode and accidentally touch something with a high voltage on it, you could easily damage the scope. In 10X mode, the worst that's likely to happen is damaging the probe.

Anything 40V and over I use the 10x.

I just about drove myself crazy wondering why I could see the ripple of AC on the DC lines, but couldn't see the DC. I thought I had all the settings correct, but still couldn't see a waveform. After realizing I wasn't going to figure it out on my own, I search the net. I figured out how to measure the voltage of DC, but still can't get a waveform. So does the DC on the B+ have a waveform? If so, how do I see it? What would be the settings other than DC coupling?

Thanks

Ideally, the B+ has no waveform at all, just a flat line of constant DC voltage. Practically, there will always be a small amount of time variation due to incomplete filtering out of the AC source (unless the device is battery powered). Even if the device is battery powered, there can be small variations due to varying load current drawn by the circuits that use the B+ supply.

Ideally, the B+ has no waveform at all, just a flat line of constant DC voltage. Practically, there will always be a small amount of time variation due to incomplete filtering out of the AC source (unless the device is battery powered). Even if the device is battery powered, there can be small variations due to varying load current drawn by the circuits that use the B+ supply.

So the flat line I see is correct. About the only thing I can do is move the coupler to GND, move the trace line to the bottom of screen, set the voltage/div, move the coupler to DC and then measure voltage after the trace line moves up. That's okay with me. :)

If I see ringing on the base of a transistor, do I look at the collector to see if the ringing has been amplified? Also, I seem to recall someone suggesting I ground the base of the ABL transistor to see if the jail bars go away. The voltage on the base is under 1V, so is it okay to ground it? Doing so won't short anything out?

So the flat line I see is correct. About the only thing I can do is move the coupler to GND, move the trace line to the bottom of screen, set the voltage/div, move the coupler to DC and then measure voltage after the trace line moves up. That's okay with me. :)

If I see ringing on the base of a transistor, do I look at the collector to see if the ringing has been amplified? Also, I seem to recall someone suggesting I ground the base of the ABL transistor to see if the jail bars go away. The voltage on the base is under 1V, so is it okay to ground it? Doing so won't short anything out?
Ringing may or may not be amplified, depends on circuit.
Grounding the ABL base will kill the ABL. If the jailbars are getting
in there they will go away. You may or may not see other changes
without ABL.
B+ lines should be clean, sometimes there is a very small amount
of hash but nothing like 5% or 10% of voltage.
With this problem you have to take things in order.
1) be sure all B+ are clean & correct
2) scope starting with the detected video from IF strip pin 5
3) work your way to the right through video til the
waveform goes "bad" thats where it gets in.

73 Zeno:smoke:

...

Ringing may or may not be amplified, depends on circuit.
Grounding the ABL base will kill the ABL. If the jailbars are getting
in there they will go away. You may or may not see other changes
without ABL.
B+ lines should be clean, sometimes there is a very small amount
of hash but nothing like 5% or 10% of voltage.
With this problem you have to take things in order.
1) be sure all B+ are clean & correct
2) scope starting with the detected video from IF strip pin 5
3) work your way to the right through video til the
waveform goes "bad" thats where it gets in.

73 Zeno:smoke:

When you say the IF strip pin 5, do you mean the one labeled "C1"? I'll post an pic of the waveform I get from the B+. It's unlike any other waveform I get. It is similar to the ringing on the ABL base, but it is a multiple waveform of about 5 or more like you're on acid and tipping. It also expands and contracts from about three to 5 or more. It's only on the B+ that I get more than a single line waveform.

I've traced the B+ to two different sources. One is from a line from the transformer that is amplified by a diode and then is tapped into the canister. From there it goes to the chroma module and makes it way around the boards. The other B+ comes from another line of the transformer and goes though a resistor and then on to the horizontal board where it connects to the pin right next to where the first B+ connects. It's a loop, but why from different lead of the transformer and why is only one end filtered by the caps?

When I get home I'll take a picture of the waveform I mentioned and post it.

You're still better off sticking to X10 unless you're at the lowest v/div setting and still can't see the signal because it's too weak. An X1 probe will tend to load down any signals you're looking at.

I'll do that. Guess I misunderstood the need for the 10x. Most of what I read and watch talked about sensitive modern circuits needing the probe. For some reason I don't think of an older television as being that sensitive with all the high voltage and other things going. :)

Okay, here are recent waveforms.

First pic is the ABL base. It measure roughly .75 volts DC and this waveform is the AC with settings of 1 volt/div and 20us time/div. Odd thing is, the AC and DC waveforms are identical.

Second pic is the ABL collector's DC waveform. It measured roughly .5 volts DC. The AC looked the same but with settings of 20m volt/div and 20us time/div.

The third pic is the B+ 125V with a setting of .5 volt/div, but with the 10x probe the display is 5 volt/div and 5ms time/div. See how fat it is? Every other wave form is a single line except for the B+ 125.

Last pic is the B+ 125V again with different settings of 1 volt/div but with the 10x probe the display is 10 volt/div and 10us time/div. The DC showed a flat line at 50 volt/div for roughly 2.5 divisions.

Okay, here are recent waveforms. The B+ measurements were done with a 10x probe, so the volt/div are actually 10x lower.


I'm not sure that I understand your use of the term "lower" in this case... For example, if the scope knob is set for 10V/div and you use the 10x probe, is the waveform measurement on the scope now? :

a) 1V/div
b) 100V/div

jr

I'm not sure that I understand your use of the term "lower" in this case... For example, if the scope knob is set for 10V/div and you use the 10x probe, is the waveform measurement on the scope now? :

a) 1V/div
b) 100V/div

jr

With the probe in the 10x mode it would be 10 volt / div. Isn't that how it works? If I set the scope to 1 volts/div and put the probe in 10x mode, it would reduce/lower/attenuate it by a factor of 10 and the display should be read as 10 volt/div?

Okay, just grounded the ABL's base leg and the jail bars remained. The only affect it had was to brighten the screen when grounded and go back to original brightness when ungrounded. So it seems the ABL circuit isn't to blame.

If I set the scope to 1 volts/div and put the probe in 10x mode, it would reduce/lower/attenuate it by a factor of 10 and the display should be read as 10 volt/div?

That is correct, the "10x" is the *attenuation* factor, not a multiplier. It was not clear that you were reporting the actual voltages of the circuit or the amplitude seen on the scope, with or without taking into account the 10x *attenuation* of the probe, or worse still using the "10x" as a multiplier.
So "b" is the correct answer to my question... agree?

Now, where do you set the baseline "0 volts" before probing a DC voltage? If probing a positive voltage, I set the baseline to the lowest line on the 'scope face and count divisions up from there after the DC is applied to the probe. If unsure of polarity, I set the baseline (with no voltage applied) to the center graticule line and see which way the trace goes when probing the voltage.

jr

That is correct, the "10x" is the *attenuation* factor, not a multiplier. It was not clear that you were reporting the actual voltages of the circuit or the amplitude seen on the scope, with or without taking into account the 10x *attenuation* of the probe, or worse still using the "10x" as a multiplier.
So "b" is the correct answer to my question... agree?

Now, where do you set the baseline "0 volts" before probing a DC voltage? If probing a positive voltage, I set the baseline to the lowest line on the 'scope face and count divisions up from there after the DC is applied to the probe. If unsure of polarity, I set the baseline (with no voltage applied) to the center graticule line and see which way the trace goes when probing the voltage.

jr

Yes, if the dial is set to 10 and the probe is on 10, then the display is 100 per division. I edited my original post to reflect the probe and dial setting.

For the DC I put set it to GND and moved the trace to the bottom of the screen and then switched to DC. It moved up as it was positive. Since the DC was showing a waveform, I moved the baseline to the top of the first division so it would show the entire waveform.

Since the DC was showing a waveform, I moved the baseline to the top of the first division so it would show the entire waveform.

Ahhhh! that's where you lost me... the reported values did not *seem" to correlate to what I was seeing on the 'scope.
jr

Ahhhh! that's where you lost me... the reported values did not *seem" to correlate to what I was seeing on the 'scope.
jr

My biggest issue is why the B+ waveform is so fat. I found that if I adjusted the trigger level I could thin it out, but then it would lose the trigger. To get it back I had to zero out the trigger level, but then I got the fat waveform. :scratch2:

I just scoped all of the B+ 125V to and from each of the modules. It was consistent throughout, if I thinned out the waveform, it was roughly 1 VPP before it lost the trigger. If you count the fat wavefrom, it would be roughly 3.5 VPP.

So I'm pretty sure 1 VPP of ringing isn't going to create the jail bars. That and I've pretty much ruled out the ABL.

Not sure where check next. I've done the horizontal oscillator, wave generator and output on the horizontal board. I don't have the probe necessary to do anything with the FB, yoke or HOT.

Without knowing the specs. for the 125V supply, it would *seem* to me that 3.5 volts of garbage would be more than I would like to see. Perhaps there are some filter caps in the 125V supply that are not functioning properly.
jr

Yes C-1 is Zeniths term for composite video. Some sets
even have a "C-1 adjust" pot.
Grounding the ABL base proves its NOT coming from there so ignore
all between the ABL base & tripler.

Depending on the scope I was using I almost never used
DC only AC since I was looking at waveforms. On my sencore
there was a built in meter to speed things up.
Also be sure all your calibrations are set. The are the red
knobs are set to "cal". Some have an arrow to show which direction
to turn them.
If the scope is dual trace you can use sync on B to stablize the
waveform. Hook the B channel probe to a clean hoz signal
such as the hoz drive collector, this may get rid of the multiple
traces.

73 Zeno

Okay, moved on the 240V boost section. I'm attaching three waveforms. Each are done at 50V/div and 20us/div.

The first is directly from the lead off the flyback where it connects to the boost diode. It's taller than my scope can display. I didn't realize it was 900V. Glad my scope didn't do something bad. I'm growing fond of it.

The second is on the other side of the boost diode and is now 248V. The waveform covers just over two divisions, so it's just over 100V and there's ringing in it.

The third is through a resistor and to the 10uf 300V capacitor. Again, I'm getting a really crappy waveform, but the basic form is the same as pic 2.

Now I tried scoping the other 240V boost, but I couldn't get a meaningful waveform. Where I scoped for pic two, it splits off from there to another point where it's connected to a 15ohm coil. It measures at 248V, but the waveform is pretty much non-existent. Don't know if it's the coil smoothing it out, or if my settings aren't working for it.

Yes C-1 is Zeniths term for composite video. Some sets
even have a "C-1 adjust" pot.
Grounding the ABL base proves its NOT coming from there so ignore
all between the ABL base & tripler.

Depending on the scope I was using I almost never used
DC only AC since I was looking at waveforms. On my sencore
there was a built in meter to speed things up.
Also be sure all your calibrations are set. The are the red
knobs are set to "cal". Some have an arrow to show which direction
to turn them.
If the scope is dual trace you can use sync on B to stablize the
waveform. Hook the B channel probe to a clean hoz signal
such as the hoz drive collector, this may get rid of the multiple
traces.

73 Zeno

I'm using the horizontal trigger of the pattern generator. Is that basically the same as using the B channel on a clean horizontal signal?

Yes, the red knobs are in the calibrated position. Not ready to mess with those kinds of adjustments. :)

When I check the C1, I get a staircase type pattern. Is that what it's supposed to look like? I have the pattern generator on the color bars w/IQW and chroma off. That gives me long b&w bars on the screen.

Inside the set there's a sheet glued to the wall. It has a section w/the heading of "Major Test Points". The first one is C1 (Picture Detector Output). The other two are used for calibrating the ACC and some IFAGC.

Without knowing the specs. for the 125V supply, it would *seem* to me that 3.5 volts of garbage would be more than I would like to see. Perhaps there are some filter caps in the 125V supply that are not functioning properly.
jr

Thing is, I can only find two capacitors and a coil on one feed of the 125V line. The caps were originally in the canister, but I replaced them when I recapped the set. That's on one end of the 125V. The other end has no caps that I can find and it is from a separate transformer. Not sure why there are two 125V feeds and from different transformers. The two leads join up at the horizontal board to complete the loop.

Now I tried scoping the other 240V boost.

I don't understand "other"... are you saying that the set actually has *two* sources of 240 Volt "boost voltage"... I suspect that there is only one source and it is distributed to other boards that may be marked "B+ or 240V", but these are boards where the 240V is used, not produced?
jr

Add: same for the 125V supply... two sources would seem to be unlikely.

How would I test the filter choke on the 125V line? My understand is it removes the AC ripples and lets the DC pass. It's specs are: Current .48ADC, DC resistance 16ohm, Inductance 75mh.

One lead of this is connected to one of the caps that used to be in the canister and the other end connects to a post where there are a bunch of boost and other diodes and also a white wire that goes up to the other capacitor that used to be in the canister.

I don't understand "other"... are you saying that the set actually has *two* sources of 240 Volt "boost voltage"... I suspect that there is only one source and it is distributed to other boards that may be marked "B+ or 240V", but these are boards where the 240V is used, not produced?
jr

Yes, it comes from the same point. The SM lists them as boost(A) and Boost(B). Boost(B) gets extra treatment by way of a coil (peaking 550uh). Not sure what that does.

So "boost B" has more filtering and therefore less noise than "boost A"?

jr

So *boost B" has more filtering and therefore less noise than "boost A"?

r

I don't know. I haven't gotten back to trying to get a trace. When I first tried, the settings used for boost(A) didn't work. I started upping the scan rate for the trigger and started to get something recognizable. I'll give it another shot tonight.

I figured the peaking coil might have done something that I need to compensate for.

Tin Can;

Your jail bars are generated in the flyback area or Horiz Yoke area, not the low voltage power supply. Not even the caps in the low voltage power supply. The low voltage PS is designed to filter out 60hz, not so much the 15K spike traveling throughout your tv. And you will see it everywhere, but its made in one spot, and its pretty strong to get everywhere....Is the size of the horiz pulse off the driver transistor the right size and shape? This drives the horiz. output transistor.

Lets see, The biggest problem to solving or making progress in this, is that all of us don't have a schematic. So, at least you should post the horiz, section, From the Horiz Osc, to the high voltage wire to the picture tube.

Also, there are things called decoupling capacitors. They take the signal generated by a noisy item and run it to ground. They are not called that on any schematic for your tv, but they are there..... They are near the horiz output circuit, it will be a 30uf cap, or less and it runs the sharp point of the horiz pulse driving the horiz output transformer to ground.

If you remember I posted a picture with lots of red dots, find similar items near the horiz. output transformer on your schematic, and begin replacing them. Check for an open coil near it, or open winding leg on the flyback that goes to a cap to ground. You should check each winding on the flyback for posted resistance to see if one is open, or changed value.

Tin Can;

Your jail bars are generated in the flyback area or Horiz Yoke area, not the low voltage power supply. Not even the caps in the low voltage power supply. The low voltage PS is designed to filter out 60hz, not so much the 15K spike traveling throughout your tv. And you will see it everywhere, but its made in one spot, and its pretty strong to get everywhere....Is the size of the horiz pulse off the driver transistor the right size and shape? This drives the horiz. output transistor.

Lets see, The biggest problem to solving or making progress in this, is that all of us don't have a schematic. So, at least you should post the horiz, section, From the Horiz Osc, to the high voltage wire to the picture tube.

Also, there are things called decoupling capacitors. They take the signal generated by a noisy item and run it to ground. They are not called that on any schematic for your tv, but they are there..... They are near the horiz output circuit, it will be a 30uf cap, or less and it runs the sharp point of the horiz pulse driving the horiz output transformer to ground.

If you remember I posted a picture with lots of red dots, find similar items near the horiz. output transformer on your schematic, and begin replacing them. Check for an open coil near it, or open winding leg on the flyback that goes to a cap to ground. You should check each winding on the flyback for posted resistance to see if one is open, or changed value.

Okay, the file was too large to upload, so I've copied portions of it into a word file and then created a new PDF. I'll attach it to this reply and hope it will work.

When I checked the horizontal pulse it was correct. I will double check it just to be 100% certain it is as should be (shape and voltage).

I'll try to locate that posting with the red dots.

So if I remove power, what else do I need to do to safely measure each winding of the flyback?

The 30uf cap you mention, is that would be an electrolytic? If so, I replaced all of them already. The only other I can find are the disc kind.

Tin Can;

....Is the size of the horiz pulse off the driver transistor the right size and shape? This drives the horiz. output transistor.

I did the H Pulse and Sweep again. While they both look like they should, the sweep is supposed to be 120V according to Sams. But with a 50 V/Div, it takes up roughly 3.5 divisions. That would make it 175V. The pulse was on 20 V/Div and it takes up 3 divisions. That makes it 60V and Sams has it as 50V.

Tin Can;

Also, there are things called decoupling capacitors. They take the signal generated by a noisy item and run it to ground. They are not called that on any schematic for your tv, but they are there..... They are near the horiz output circuit, it will be a 30uf cap, or less and it runs the sharp point of the horiz pulse driving the horiz output transformer to ground.

I found the cap running off the horizontal output transformer. It's a 47uf and was replaced.

I'm glad I started looking at the caps in the horizontal area. Seems when I recapped I put the 10uf 50V cap in backwards. It was my fault as I didn't have a radial and didn't want to order just for one cap. I went through my supply and found some of the audio grade Nichicon. I thought I was installing a KW series which has gold band for negative, but I put in an FW which has black for negative so the gold casing threw me off and I installed the negative based on the gold side. Odd it didn't explode, though.

Anyway, the cap has been replaced and the backwards one not reads as 5uf instead of 10uf. Don't know what it was doing to the set (if anything), but it sure didn't have anything to do with the jail bars as they're still there.

I also thought I put in the 47uf on the horizontal output transformer as it had + on ground, but looking over the schematics and pictures I took before the recap, it is supposed to be that way. Looking over all other caps while I was under there shows those are all installed correctly.

I don't see the HV supply on the schematic... which page is it on?

jr

I don't see the HV supply on the schematic... which page is it on?

jr

Do you mean the flyback (T207)? If so, it's on the second page bottom center. If that's not it, I'm not sure as I thought it was the HV supply.

Thanks! I found it.
jr

Good morning;

Ok, lets begin with your scope. It needs to be checked for some level of calibration. This can be done by you at home for a very little amount of money. You need to get a series of 9v batteries, hook them up to give you 18v, 56v, then check the voltages with a volt meter, write it down. Then use your scope, - lead to ground on scope, hit the + battery with your scope probe. If you have to make a circuit with a momentary contact switch and hook up your wires and watch your scope. You should be able to verify your scope is reading the proper voltage range this way.

You mentioned two spots where your voltages might not be correct. These need to be investigated. This is the way you will find this problem.

As an example, lets look at a audio amplifier, one with a pilot light on it. If you run it at some mid volume, the sound will be clear. If you turn it up to saturation, especially bass, it will distort, and in most cases the pilot light will begin to dim with the bass notes. Your jail bars are coming from something that is allowed to saturate, something in the horiz, output area, and it is ringing, and you see it everywhere in the tv, just like in the audio amplifier saturation blinking the pilot light. If your set were working correctly, this would be filtered out, but a spike it too large and showing up in places it should not. While the jail bars may show up in many places, it can only be fixed by removing it at the source, the horiz section of the tv.

In these sections in the pictures I am posting, you need to be sure all of the voltages, wave forms, are correct. There will be some clue, voltage wrong, wave shape wrong, open coil, changed resistor, something. Start with the Horiz driver, then go to horiz output, then flyback. Focus on the items in the three pictures I am uploading. If the voltages or wave shapes, sizes of wave shapes, p-p voltages are wrong, do not go on to the next stage. Check everything listed, voltages, wave shapes and sizes peak-to peak dc offset if its there. If the osc, driver section (left picture) has something not right, stay there until it is.... Do not go on to the center picture items.

Start with the left picture, then center, then right.

Good morning;

Ok, lets begin with your scope. It needs to be checked for some level of calibration. This can be done by you at home for a very little amount of money. You need to get a series of 9v batteries, hook them up to give you 18v, 56v, then check the voltages with a volt meter, write it down. Then use your scope, - lead to ground on scope, hit the + battery with your scope probe. If you have to make a circuit with a momentary contact switch and hook up your wires and watch your scope. You should be able to verify your scope is reading the proper voltage range this way.

You mentioned two spots where your voltages might not be correct. These need to be investigated. This is the way you will find this problem.

As an example, lets look at a audio amplifier, one with a pilot light on it. If you run it at some mid volume, the sound will be clear. If you turn it up to saturation, especially bass, it will distort, and in most cases the pilot light will begin to dim with the bass notes. Your jail bars are coming from something that is allowed to saturate, something in the horiz, output area, and it is ringing, and you see it everywhere in the tv, just like in the audio amplifier saturation blinking the pilot light. If your set were working correctly, this would be filtered out, but a spike it too large and showing up in places it should not. While the jail bars may show up in many places, it can only be fixed by removing it at the source, the horiz section of the tv.

In these sections in the pictures I am posting, you need to be sure all of the voltages, wave forms, are correct. There will be some clue, voltage wrong, wave shape wrong, open coil, changed resistor, something. Start with the Horiz driver, then go to horiz output, then flyback. Focus on the items in the three pictures I am uploading. If the voltages or wave shapes, sizes of wave shapes, p-p voltages are wrong, do not go on to the next stage. Check everything listed, voltages, wave shapes and sizes peak-to peak dc offset if its there. If the osc, driver section (left picture) has something not right, stay there until it is.... Do not go on to the center picture items.

Start with the left picture, then center, then right.

The scope was professionally calibrated when I got it a couple of weeks ago. I know it reads the same voltage I get with my DMM.

Tomorrow I'll start on your list. I know it's not the horizontal driver as I replaced the module with a newer, NOS board and have the same problem. That module has the wave shaper, horizontal AFC, OSC and driver. The module isn't the source, but it could be affected by it.

I do have a question, though. On the schematics for the H. Sweep it says that point is T5 and is 63.7V. However, the waveform shown for that point says it's 120VPP. How is that? How can you get a 120V PP with a driving voltage of 63.7V?

This is the point I had a 160V PP. That will be my first recheck tomorrow morning. Today is a complete mess and no time for the poor set.

I do have a question, though. On the schematics for the H. Sweep it says that point is T5 and is 63.7V. However, the waveform shown for that point says it's 120VPP. How is that? How can you get a 120V PP with a driving voltage of 63.7V?.

The 63.7V is the DC voltage you should read if you measure that point with a DMM. The 120 Vpp is the amplitude of the AC waveform present.

The waveform looks to be roughly 50% duty cycle (pretty close to a square wave), and if it oscillates from 0 to 120V peak, the average voltage would be around 50% of 120V, or somewhere around 60V. 63.7 sounds like a perfectly reasonable reading to expect on a DC voltmeter.

Did you ever sit through that scope training course? Real basic stuff like this really needs to be understood before you can really hope to be able to repair a TV except by sheer luck...

The test point may contain information that can be interpeted 2 different ways. With a scope, you will see the entire wave, peak to peak. Your volt meter depending on design will read whatever it is designed to read, some will read and store peak, some will read average, and most will read some type of R.M.S. this is a area under the curve calculus derived average voltage. The schematic often details how all readings are taken, and in some cases even details the type and model instrument used, (or equiv.) is often written. Your RMS voltage will depend on the quality of your meter, and the old expensive ones did say what frequency you can use it and expect a certain level of accuracy. I don't know what new ones say in the instructions...

It is important to be sure your test equipment is reading correctly, or you will be chasing something that does not exist. A calibrated ebay piece of equipment means squat unless you do a little checking to be sure it really is what it is....

If tp5 is not reading correctly, your problem may be right there, everything very near that point needs to be checked.

Funny thing about man made stuff.... Sometimes one model of something all have the same problem. So don't overlook something just because you got a replacement somewhere.... Go by what good troubleshooting skills are taking you towards.

The 63.7V is the DC voltage you should read if you measure that point with a DMM. The 120 Vpp is the amplitude of the AC waveform present.

The waveform looks to be roughly 50% duty cycle (pretty close to a square wave), and if it oscillates from 0 to 120V peak, the average voltage would be around 50% of 120V, or somewhere around 60V. 63.7 sounds like a perfectly reasonable reading to expect on a DC voltmeter.

Did you ever sit through that scope training course? Real basic stuff like this really needs to be understood before you can really hope to be able to repair a TV except by sheer luck...

Yep, I watched it. I was pretty much on the right track and just needed a few visual instructions to understand the rest. I can now do all the basics and am learning more each day.

The test point may contain information that can be interpeted 2 different ways. With a scope, you will see the entire wave, peak to peak. Your volt meter depending on design will read whatever it is designed to read, some will read and store peak, some will read average, and most will read some type of R.M.S. this is a area under the curve calculus derived average voltage. The schematic often details how all readings are taken, and in some cases even details the type and model instrument used, (or equiv.) is often written. Your RMS voltage will depend on the quality of your meter, and the old expensive ones did say what frequency you can use it and expect a certain level of accuracy. I don't know what new ones say in the instructions...

It is important to be sure your test equipment is reading correctly, or you will be chasing something that does not exist. A calibrated ebay piece of equipment means squat unless you do a little checking to be sure it really is what it is....

If tp5 is not reading correctly, your problem may be right there, everything very near that point needs to be checked.

Funny thing about man made stuff.... Sometimes one model of something all have the same problem. So don't overlook something just because you got a replacement somewhere.... Go by what good troubleshooting skills are taking you towards.

The scope was calibrated by Teletek using N.I.S.T. standards and certified by them. I have a certificate of calibration. I also get a free calibration within one year, but they're up north and I don't know how practical it would be shipping to and from.

Okay, so how about this. I have tested it on DC and it reads correctly. For AC, can I check an outlet? I have a meter that plugs into the outlet and shows the voltage. It has an outlet to plug things in and measure wattage, etc. Can I use the scope to see if it reads the same AC voltage as the meter? Would also be interesting to see how noisy the AC line is.

Can I use the scope to see if it reads the same AC voltage as the meter? Would also be interesting to see how noisy the AC line is.

I would *NOT* try that...I believe that the scope chassis and therefore the probe "ground" clip are indeed connected to earth ground through the power cord... if you happen to connect the probe ground clip to the "hot" side of the line sparks will fly !

jr

As to AC line voltage: if its a two-channel scope, you get two identical probes
and use one of them on the hot side, one on the cold (not ground wire) and
use the difference setting. You don't attach the ground lead of either probe
to anything ... the scope case is connected to the power line ground already.

You really need to be careful anytime you connect any plug in test equipment to ground on anything you are working on. You should always use a battery volt meter and check ground on test equipment to ground on your test subject item, If there is a wiring inconsistency either in your bench items, or house wiring, you will see 120v across the two grounds, if you then connect them, yes you will have your own semi-private fireworks show.

Okay, there seems to be an issue with the "Trig view" button. When I measure AC in the 50V / Div setting, it covers 7 divisions. I know that's not correct. So when I push the "Trig View" I get the proper waveform and the right number of divisions (2 1/2 divisions). That same button, if you pull it, is the bandwidth limiter. If I play with the button, it eventually shows the proper waveform height. If I touch it again, it gives the expanded waveform again. It's like it's dropping from 50V/div to the next lower setting.

It could be a dirty contact in the switch. I'm going to contact the company I got it from to see if it's okay to give it a shot of Deoxit. If I can't get it going I'm going to have to send it back for repair.

You really need to be careful anytime you connect any plug in test equipment to ground on anything you are working on. You should always use a battery volt meter and check ground on test equipment to ground on your test subject item, If there is a wiring inconsistency either in your bench items, or house wiring, you will see 120v across the two grounds, if you then connect them, yes you will have your own semi-private fireworks show.

So I should put the meter between the ground of the chassis and ground of the probe and look for voltage? If I see voltage I should reverse the plug to see if it makes it better? How much is acceptable?

...

Actually, that is correct. The wall outlet is supposed to be about 120v RMS. You're looking at peak to peak voltage on the scope. Divide the p-p voltage by 2 to get peak voltage (350v p-p is 175v peak). Divide the peak voltage by the square root of 2 to get RMS (123.7v RMS in your case).

Also, you need to know that most AC volt meters are designed to read AC voltages as RMS, but that it only works for a pure sine wave like the AC power line. For anything else (like a square wave), it will be wrong unless it's a "true RMS" meter.

Well then I feel better. Now I need to get back into the set to recheck the horizontal sweep as the PP I got put it at 160V and the Sams says it should be 120V. Since the board is driven by the 125V B+, I don't see how it could be putting out a 160V waveform.

Fun stuff, fun stuff.

I would *NOT* try that...I believe that the scope chassis and therefore the probe "ground" clip are indeed connected to earth ground through the power cord... if you happen to connect the probe ground clip to the "hot" side of the line sparks will fly !

jr

I was just going to touch the tip of the probe to the hot side and leave the ground clip disconnected.

I was just going to touch the tip of the probe to the hot side and leave the ground clip disconnected.

Good! I just thought that I should pass on a lesson that I learned the hard way. :) Early 'scopes that I used (Heathkits mostly) were not grounded through the power cord, so I had quite a surprise when I connected my first *grounded* Tek scope to a hot chassis radio! :eek:

You likely introduce a bit of error by single tip probing, because the scope earth ground may be a slightly different voltage than the "ground" side of the line. The *best* measurement would be obtained by the 2 tip/2 channel "differential" method, described by dtvmcdonald in a post above. Accurate, and safe for the 'scope

jr

""
Well then I feel better. Now I need to get back into the set to recheck the horizontal sweep as the PP I got put it at 160V and the Sams says it should be 120V. Since the board is driven by the 125V B+, I don't see how it could be putting out a 160V waveform.

""

Is the B+ correct ? are all the B+'s however many there are correct ?
How about B Boost over by the HOT ?

""
Well then I feel better. Now I need to get back into the set to recheck the horizontal sweep as the PP I got put it at 160V and the Sams says it should be 120V. Since the board is driven by the 125V B+, I don't see how it could be putting out a 160V waveform.

""

Is the B+ correct ? are all the B+'s however many there are correct ?
How about B Boost over by the HOT ?

The B+ is at 129V and the B+ Boost is 247 and the same voltages at all their connections points. I'll have to check the other B+s that are in the 20V range. I believe there are two of them (one around 23V and the other around 29V).

as long as those larger ones are under control, don't worry too much about the smaller ones right now.... Stick to the ones you are getting that look too high. tp5.

as long as those larger ones are under control, don't worry too much about the smaller ones right now.... Stick to the ones you are getting that look too high. tp5.

Okay, went after the TP5 again. My DMM has it at 134VAC, but my scope has a PP of 170V. Am I missing something? I guess I'll find some other TPs and see if their voltage matches the waveforms in Sams. If they, then something is wrong with TP5. If they don't, then it's my scope and/or probe or Sams is not accurate.

With the scope on 50V/Div and putting the probe near the FB, I get this waveform. If you notice, the bottom of the form is ringing the number of jail bars I see on the screen. Is this normal to see this when probing w/out actually making electrical connection to the FB? I get the same form when placing the probe on the collector of the HOT (plastic tip on probe). It's even worse if I go anywhere near the focus wire.

as long as those larger ones are under control, don't worry too much about the smaller ones right now.... Stick to the ones you are getting that look too high. tp5.

Okay, just checked the horizontal pulse which should be 50VPP. I set my scope to 50V/Div and got the noted waveform in Sams as well as a PP of one division. So that one is correct, so the scope seems to be working properly. I've found another TP I'm going to try. It goes to the convergence board and is 170VPP. That should tell me if my scope and/or probe is handling higher voltages correctly.

Okay, so how do I go about checking my scope for proper AC voltage calibration? I just tested another point that is supposed to be 170VPP. With the scope on 50V/Div I get almost 4.5 divisions. That's almost 225VPP. I checked with my DMM and it reads as 130VAC. I check the one next to it that was supposed to be 20VPP and it showed as 25VPP. The DMM had it as 16.9VAC. I'm pretty sure my DMM isn't showing the exact voltage (everyone keeps writing about RMS and such).

I need to know if there's something wrong with my scope. If so I need to return it to be fixed.

Thanks!

Who makes your dmm, where did you get it, and how much$.

The pins at the horiz board, tp5 is 123, next one down is 124, and bottom is 6. The schematic you posted is not that clear, and gets worse when I blow it up, so If you check the voltages at each one of these points, are they correct, higher, lower?
You need to post "posted" value as in (sams) and actual, (what you read), How DMM Scope.

How about the wave form at the base of the HOT? is it good?

The diode, and cap in the collector circuit closest to the HOT on the schematic? they good?

Does the schematic detail the meter used ? for sams voltage readings?

...

Hopefully, this step is completed already..... Remember the scope videos we talked about looking at earlier.

The first thing to do is to check the calibrator output on the front of the scope. You should see a perfect square wave with the amplitude specified. If the top and bottom is curved, then adjust the probe (this applies to X10 mode only).

Comparing things to the Sams folder is a bad way to check your scope for accuracy. Sams often have mistakes, many of the circuits in the TV (which isn't working properly) have wide tolerances, and your 465 probably has 10 times the bandwidth as the one Sams used (meaning high frequency signals, and fast pulses will appear larger on your scope).

Yes, the calibrator is 1V and with the probe in 1x and .5V/Div I get a perfect square wave. I then put the probe in 10x and 50m/Div and get another perfect square wave.

See my other post where the 125VAC shows up as 325V on the scope.

Hopefully, this step is completed already..... Remember the scope videos we talked about looking at earlier.

Yes, I've sat though hours of videos including the 2hr+ training. I truly believe I'm doing the settings correctly.

How about I do the horizontal sweep again and when the 170VPP waveform comes up I take a picture of the entire front of the scope so all the settings can be seen?

Who makes your dmm, where did you get it, and how much$.

The pins at the horiz board, tp5 is 123, next one down is 124, and bottom is 6. The schematic you posted is not that clear, and gets worse when I blow it up, so If you check the voltages at each one of these points, are they correct, higher, lower?
You need to post "posted" value as in (sams) and actual, (what you read), How DMM Scope.

How about the wave form at the base of the HOT? is it good?

The diode, and cap in the collector circuit closest to the HOT on the schematic? they good?

Does the schematic detail the meter used ? for sams voltage readings?
My DMM is a Craftsman and is about 13 yrs old. (See pic)

I will check those other points and post their voltage and the Sams voltages.

I was told that the diode on the HOT had to be good since the HOT would be dead if it wasn't. As for the capacitor, I didn't test. Can I use an ESR meter to test it? I believe if I pull the hot, I should be able to test that capacitor without disconnected a leg an it should be pretty much isolated at that point.

I will put the set on her side and remove the bottom to get the waveform of the base of the HOT.

Your camera will adjust to the brightest items, so set the trace very dim, and the graticule very dim as well. You can set the sweep to display one or two cycles of the pulse, just turn the knob to what you want. Set the vert volts/div. so you get close to a full screen, it will be easier to read that way..... you know 3 to 4 divisions is more accurate than say 3/4's of a cm..... or 3/4's division...

Your camera will adjust to the brightest items, so set the trace very dim, and the graticule very dim as well. You can set the sweep to display one or two cycles of the pulse, just turn the knob to what you want. Set the vert volts/div. so you get close to a full screen, it will be easier to read that way..... you know 3 to 4 divisions is more accurate than say 3/4's of a cm..... or 3/4's division...

Okay, let's see how this goes. Here's a pic of what Sams has for T5 and what I got on the scope w/full face of scope so you can verify settings. If something isn't clear in the pic, let me know and I'll fill you in.

EDIT: Added a third pic as you can't read the face without the flash lighting it up.

ok, so its about 3.5 divisions, which v/div are you using? what does it work out to be...?

just under 175v if you are using 10x probe?

Lets try something a little different....

Measure that same spot using d.c.
1. put the scope on gnd. using that 3 position switch input for channel 2
2. move the display trace to a lower line on the grid, using the position knob.
3. turn the 3 position knob to dc, then measure the 125v source, see that it reads 125.
4. check tp5 again, see if it saturates at what the 125v source is...

ok, so its about 3.5 divisions, which v/div are you using? what does it work out to be...?

just under 175v if you are using 10x probe?

That is correct.

Lets try something a little different....

Measure that same spot using d.c.
1. put the scope on gnd. using that 3 position switch input for channel 2
2. move the display trace to a lower line on the grid, using the position knob.
3. turn the 3 position knob to dc, then measure the 125v source, see that it reads 125.
4. check tp5 again, see if it saturates at what the 125v source is...

I followed each step and got the attached pics. The DC of the 125V source (B2) reads just under 140VDC (with my DMM I get 130VDC). When I then check the DC of T5, I get 175V. This is with the same v/div as the previous test (50V/Div).

At this point, I am going to assume your 125v source may be 140V.
You are also seem to be having different readings on your two pieces of test equipment. You will have to figure out how you want to deal with that.

I would check through the low voltage power supply where the 125v comes from, and check through the voltages listed there, there should be 4 or 5 low supply spots you can test, Use both your dmm, and the scope on DC, see which one you are more willing to trust. If that 125v is way off, then your HV may be using too much power and creating that ring just because the voltage is too high....

If you can, please post the power supply circuit, lets see if its a doubler with a possible bad part making too much voltage.....

I'm sorry to be casting doubt on your test equipment, but I have been there before, it may seem to be a stupid step, but we have to follow the evidence we have to find the real problem.

Here's my results with the base of the HOT. I'm attaching the Sams waveform (not very clear) and mine. I had my scope set on 2V/div and as you can see it filled the display. It's about 16V. The Sams has it as 7V.

At this point, I am going to assume your 125v source may be 140V.
You are also seem to be having different readings on your two pieces of test equipment. You will have to figure out how you want to deal with that.

I would check through the low voltage power supply where the 125v comes from, and check through the voltages listed there, there should be 4 or 5 low supply spots you can test, Use both your dmm, and the scope on DC, see which one you are more willing to trust. If that 125v is way off, then your HV may be using too much power and creating that ring just because the voltage is too high....

If you can, please post the power supply circuit, lets see if its a doubler with a possible bad part making too much voltage.....

I'm sorry to be casting doubt on your test equipment, but I have been there before, it may seem to be a stupid step, but we have to follow the evidence we have to find the real problem.

I'll check all the points of the 125V from the point it leaves the transformer to various points using both DMM and scope.

I've attached a pic of the power supply section.

Well, that 16v is generated in the coupling transformer. So for that to be too high, all other stuff being good, the primary has to be getting too large a signal, and you have evidence of that. So the thing to do is try and figure that out....

Is the power supply too high?

or

is there something making the primary signal too high?

I am leaning towards double checking the power supply, that 125, and what else may be associated with it, be it larger or smaller sources that may be there.... Please post the power supply section when you get a chance, ( Isee it thanks ! ) and measure the different sources available....

And just in case the power supply is pumping out too much voltage, lets limit how long you keep the set on to just 10 minutes or so during each measurement period.

Be careful when measuring the power supply, if its regulated, you don't want to accidentally short anything that will fry anything in there....

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

I'll do these next. I've been going over the 125V sources and they all show up as 129V. The DMM and scope are in agreement there. I also checked the 125VAC and did the math. The DMM showed 128V and the scope had 126V after doing the calculation given me for RMS.

I'll let you know the voltages asked for.

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device? :scratch2:
jr

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

The voltage to and from the regulator (Q212) is correct. I get 23.4V and 24V. Each is only off by .2, but that's most likely my DMM. The scope also showed the proper divisions from baseline for DC.

I thought that 3.5uf canister wasn't soldered in, but it is. It's also 440V. What size resistor will I need to discharge it?

...

128v at the diode there just before the filters and choke.

Okay, on the AC side of the diode I get 131VAC and on the other side I get 131VDC. According to the schematics, the Red-Blk is supposed to be 100VAC. So if I test directly to where the Red-Blk connects, I shouldn't seem much more than 100VAC, right?

Here's a pic of the red-blk connection and the 3.5uf 440V cap. If you think this cap needs to be checked, let me know. I'll have to unsolder one of the leads.

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device? :scratch2:
jr

That transformer supply is ferroresonant - an L-C tank, and causes the transformer to provide some level of regulation itself. If the 440V cap goes bad, you'd know it, with a dead set, or really low voltages. If you get B+ and other transformer secondary voltages, move on, as the ferroresonant circuit is working. Zenith stressed this after seeing a spike in folks ordering the cap. Reliability testing showed the cap had a 40+ year life, and shops that didn't understand the circuit would order and replace the cap to eliminate that as the cause of whatever problem they had. I've only seen one go bad- and a dead set was the result, with the blown input fuse as well.

We always kept the caps from the sets we junked, and I used one two summers ago as a makeshift run capacitor in my HVAC Gaspack to keep the AC going in July 2011. Date code on the cap is 1979....

Cheers,

It doesn't look that bad to me. I think your scope is showing more of those sharp negative going pulses than what ever scope Sams used. If you ignore that really fine negative pulse, it ends up being around 8-10 volts which is well within reason. I doubt Sams would have used a 100MHz oscilloscope because no technician in the 70's would have had anything even close to it.

I can just about guarantee nothing in the HOT base drive circuit is causing your jail bars. Generally, if there's anything wrong with the base drive, the HOT will overheat and fail. The HOT acts as a switch. It's either completely on, or off.

I think you need to be looking around the flyback, and yoke. Something is causing the flyback, or yoke to resonate at about 10x the horizontal scanning frequency. It's not going to be caused by a slightly wrong drive signal, or slightly off voltage.

Have you looked at L218 and C274?

Okay, just to make sure, is this attached pic of the L218 you're referring to (the brown cylinder with the coil around it)? It took me a moment to find, but it is connected to tie points 3 and 4. I should check its resistance and see if it matches what Sams has across tie points 3 and 4? Also, I can't find the capacitor shown (the .047).

You have any tips on checking the yoke? I've been trying, but I can't see to get any meaningful results. I've tried checking pin pairs, but according to the schematics, each has multiple connection points. So how am I supposed to check the resistance? All I can really do is check continuity. The first pair I tried should have a resistance of 220ohm, but my meter shows me 8ohms.

Have you looked at L218 and C274?

Okay, I checked L218 and I got .7. It's supposed to be .12, but I checked and my leads are .6. So subtract the leads and I get .1 (my meter doesn't show anymore places to the right).

I think I found the capacitor. It's red and axial and there are actually two of them. Is this them in the pic?

Okay I finished the testing of the FB. I don't know how accurate it is as my leads seem to have .6 resistance of their own and I don't know if that should be disregarded or subtracted. I usually disregard it, but the numbers I'm looking at for the FB are pretty low and if .6 is added by the leads, it could easily triple some of the results. So if anyone knows what should be done in this situation, let me know.

I'm attaching the FB section of the schematic so you can see where/what I tested.

Below are the connections, the results w/out subtracting me leads and the values on the schematic. The first three are at the tie points on the board next to the FB. The rest were done at the chassis connections of the FB leads.

Connections Results Sams
3 - 9 / .8 / .1
4 - 8 / 2.2 / 1.6
9 - yoke plug / .12 / .5

G - R/W / .10 / .5
R/W - Blk / .8 / .7
Y - Blk / .7 / .1
Y - Vio / .8 / .2

I don't know if anything is thrown off by all the leads being connected to the chassis still. Nothing in the Sams says anything about tolerance, so I don't know how close or dead on they have to be.

I'm happy your check of the low voltage power supply went well. As long as the 125v is not as high as 140v and your measurement of the 24v regulated showed the same readings on both test instruments, lets go back to tp5. I know there are not many who believe something can be wrong here, but there has to be a reason the drive voltages are so far off. I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.

In that picture you posted of the flyback, is it melted or is that some repair made to it ? its not running hot is it?

Sams gives an emitter current for the HOT on that schematic, I think it say 1.8A, if you think its running hot, it may be worth measuring that.... You have to use the 10A DC current scale on your DMM, - to ground + to the emitter. Only if you think its running hot..... or the FB is melted....

I'm happy your check of the low voltage power supply went well. As long as the 125v is not as high as 140v and your measurement of the 24v regulated showed the same readings on both test instruments, lets go back to tp5. I know there are not many who believe something can be wrong here, but there has to be a reason the drive voltages are so far off. I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.

In that picture you posted of the flyback, is it melted or is that some repair made to it ? its not running hot is it?

Sams gives an emitter current for the HOT on that schematic, I think it say 1.8A, if you think its running hot, it may be worth measuring that.... You have to use the 10A DC current scale on your DMM, - to ground + to the emitter. Only if you think its running hot..... or the FB is melted....

The two caps you noted between the coupling transformer are new and were tested before installation (jail bars were there before the replacement).

I think you're looking at the blob of RTV covering the lead so it doesn't arc from the top of the flyback to any metal in its surroundings.

The HOT runs around 81 degrees and cool to the touch (well not cool, but barely registers to the touch as it's no hotter than my fingertips).

I'll pull the horizontal board today and check the values of the cap and resistors noted. If they are okay, I'll put it back and scope the H-OSC transistor.

Gotta catch up on some other duties this morning, but will be back inside the set in a couple of hours.

[QUOTE=Username1;3084085]I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.QUOTE]

Okay, finished testing what you noted. The 20pf (C814) is 19.8, the 2Kohm resistor (R821) is 2.5Kohm (this one has no percentage band so I don't know if that's too far off), the .22uf (C811) is .23uf and the 40ohm resistor (R819) is 47ohm.

Do you want me to test the voltage of all three legs of (Q803)? Do you just want DMM readings, scope or both? This little bugger's a pain as it's right behind the large capacitor and it's a pain to get the hooks on the legs.

Yah, I would like to know what the voltages are on that driver transistor....
No need for the scope, the shape on the output looks ok, so no need.
q803. Follow the trace to the next component if its more convenient to take a voltage reading. You can measure off the resistor, that 40 ohm, just get the side that goes to the transistor... Same with the base, get it off the r814, one side is ground.... 180 ohms another 5% resistor...

That 40 ohm resistor says it should be 5%, but its off by more than 10%..... close to 20% off.....
Any discoloring on that resistor....

Was that HV Transformer arcing? did you add that silicone to the HVT?
Do you have any idea if the HV to the picture tube is on target, high or low...?

If you were to take out the HOT and check the voltage at tp5, does it come back to normal....? Not sure if you have run the set without it in there or not....? Not entirely sure if its safe, I would think it is....

Yah, I would like to know what the voltages are on that driver transistor....
No need for the scope, the shape on the output looks ok, so no need.
q803. Follow the trace to the next component if its more convenient to take a voltage reading. You can measure off the resistor, that 40 ohm, just get the side that goes to the transistor... Same with the base, get it off the r814, one side is ground.... 180 ohms another 5% resistor...

That 40 ohm resistor says it should be 5%, but its off by more than 10%..... close to 20% off.....
Any discoloring on that resistor....

Okay, got in there with a small j-hook. The Collector is 68V (Sams 63.7V), Base is 2.28V (Sams 2.42V) and Emitter is 2.68V (Sams 2.07V)

Sorry, I have added stuff above....

That diode in the HOT collector, is that been tested, and do you know if its the right one? It would need to be a high speed diode, not a power supply 60hz diode, but a fast one...

And I see there is a 1.5 ohm resistor on the secondary of the coupling transformer going to the HOT base, is that 1.5 ohm resistor been checked...?
goes to ground, and one leg of that transformer, secondary.

Sorry, I have added stuff above....

That diode in the HOT collector, is that been tested, and do you know if its the right one? It would need to be a high speed diode, not a power supply 60hz diode, but a fast one...

I got 442 in one direction and 1232 in the other direction yesterday, but that's with the HOT installed. If I remove the HOT, will I be able to get a better reading or do I need to lift a leg? I'm pretty sure the 1232 should be infinity and the HOT might be interfering with the readings.

I couldn't tell you if it's the correct one, and I do have an NOS replacement if needed. The replacement isn't a cylinder like the current one. It's shaped kind of like a barrel.

Yah, I would like to know what the voltages are on that driver transistor....
No need for the scope, the shape on the output looks ok, so no need.
q803. Follow the trace to the next component if its more convenient to take a voltage reading. You can measure off the resistor, that 40 ohm, just get the side that goes to the transistor... Same with the base, get it off the r814, one side is ground.... 180 ohms another 5% resistor...

That 40 ohm resistor says it should be 5%, but its off by more than 10%..... close to 20% off.....
Any discoloring on that resistor....

Was that HV Transformer arcing? did you add that silicone to the HVT?
Do you have any idea if the HV to the picture tube is on target, high or low...?

If you were to take out the HOT and check the voltage at tp5, does it come back to normal....? Not sure if you have run the set without it in there or not....? Not entirely sure if its safe, I would think it is....

The RTV, I believe, is factory. Doesn't look like it's ever been disturbed. It's also on the tripler end.

I don't have an HV probe, so I couldn't tell you. This makes me think of something I've been meaning to ask. Whenever they talk about safety they get on the fact you need to discharge the CRT at the anode. They say to use a screwdriver connected to ground. So I take a long screwdriver, clip an alligator clip lead to it and clip the other end to chassis ground. I then slip the tip under the cap and touch the connection. They say you should hear a "snap" and should do it a couple of time. I've done this several times while working on this set and not once this it make a noise or give any indication that it discharged. Last time I took out the chassis I just turned off the set, pulled the plug and in less than 3 minutes later I tried to discharge and nothing.

When I killed the HOT the other week, I ran the set without it (was the only way to keep the circuit breaker from going. I don't see why I couldn't remove it and measure T5 again. Do you want just a DMM voltage or a scope waveform?

Well here is my thinking...
The horiz driver transistor, 67v 2.x, and 2.x tells me that it looks to be within reason given something is wrong elsewhere in the immediate area.

The large signal on the base of the HOT leads me to think possibly open 1.5 ohm resistor in the secondary of the coupling transformer... You should check that.

Then there is that diode in the collector of the HOT. That diode is to arrest, or stop a sharp negative pulse coming from the HVT when the transistor turns off. If this diode was not turning on fast enough would there be a sharp negative pulse there, and would it be traveling back to the coupling transformer???? It could also be allowing the HVT to be producing those jail bars.... Its all reason, What's going on, and testing. There are some clues around that area, so its just trying to see what part could reasonably be bad, still let most of it work properly, but still be causing some minor problems.... That doide, If you have a new one, might be smart to put it in since it will be spec. when you do....

And on that picture tube discharge, on all tube sets there is more likely a long term charge held, but on a trippler set there are little bleeder resistors, and leakage through the caps in there, more so than a tube rectifier alone...
While its best practice to discharge always, if there is no change, don't loose sleep over it.

Well here is my thinking...
The horiz driver transistor, 67v 2.x, and 2.x tells me that it looks to be within reason given something is wrong elsewhere in the immediate area.

The large signal on the base of the HOT leads me to think possibly open 1.5 ohm resistor in the secondary of the coupling transformer... You should check that.

Then there is that diode in the collector of the HOT. That diode is to arrest, or stop a sharp negative pulse coming from the HVT when the transistor turns off. If this diode was not turning on fast enough would there be a sharp negative pulse there, and would it be traveling back to the coupling transformer???? It could also be allowing the HVT to be producing those jail bars.... Its all reason, What's going on, and testing. There are some clues around that area, so its just trying to see what part could reasonably be bad, still let most of it work properly, but still be causing some minor problems.... That doide, If you have a new one, might be smart to put it in since it will be spec. when you do....

And on that picture tube discharge, on all tube sets there is more likely a long term charge held, but on a trippler set there are little bleeder resistors, and leakage through the caps in there, more so than a tube rectifier alone...
While its best practice to discharge always, if there is no change, don't loose sleep over it.

Okay, I'm going to pull the chassis and change out the diode and the 1.5ohm resistor. I have purchased all new resistors for that area in case of finding any bad ones.

If you can think of anything else while the chassis is out, that would be great. It's much easier to test/replace when it's on the bench.

I know its trying to be taken in different directions by different people with ideas about what can be wrong. I'm quite surprised you have not called us all a bunch of nuts by now and thrown that tv off the roof and went and got another off CL for free or $10. and just said the hell with it...... : )

If its not right in that area of the coupling transformer, that diode, open resistor, then it's got to be the pink fairy inside the flyback, she probably can't get any air cause of that extra silicone on it.....

I know it's a Letterman thing, but you may be able to plead your case to Lenno, he's on your coast, maybe he'll make an exception and do a Letterman and toss it off a roof for you and put it on national tv..... Could be the best solution to the problem...

I know its trying to be taken in different directions by different people with ideas about what can be wrong. I'm quite surprised you have not called us all a bunch of nuts by now and thrown that tv off the roof and went and got another off CL for free or $10. and just said the hell with it...... : )

If its not right in that area of the coupling transformer, that diode, open resistor, then it's got to be the pink fairy inside the flyback, she probably can't get any air cause of that extra silicone on it.....

I know it's a Letterman thing, but you may be able to plead your case to Lenno, he's on your coast, maybe he'll make an exception and do a Letterman and toss it off a roof for you and put it on national tv..... Could be the best solution to the problem...

I've spent years looking for this set. I'll either fix the jail bars or learn to live with them.

Okay, she's got the new damper diode and the 1.5ohm resistor. The resistor tested as 1.8 and the one I replaced it with was dead on 1.5.

I also tested the resistance of the coupler transformer and one side was pretty much dead on at .23ohm (Sams has .25) and the other side was 92ohm (Sams has it at 100ohm).

She's been running for a little bit now and nothing blew up. The jail bars are still there, though. Not sure where to go next.

I'm not too sure what to think of next either....

Well, you know about now, I would be taking a small cap and jumping those caps after the collector of the HOT with the set on and watching the screen to see what it does.... Not recommended, But if you ran across a spot that made a change in those jail bars, it might be worth it....

Do you think anyone ever removed a metal shield from somewhere and never put it back ?

I really don't think its in the yoke, so it's probably a bad yoke....

I'm not too sure what to think of next either....

Well, you know about now, I would be taking a small cap and jumping those caps after the collector of the HOT with the set on and watching the screen to see what it does.... Not recommended, But if you ran across a spot that made a change in those jail bars, it might be worth it....

Do you think anyone ever removed a metal shield from somewhere and never put it back ?

I really don't think its in the yoke, so it's probably a bad yoke....

Those caps after the HOT are all the safety caps. They're all new.

All the shields seemed to be in place when I got it. The only one removed was when I put in a new, updated, subcarrier regen module. It was redesigned with a small shield on it to protect from interference. The last person to adjust the APC stripped the plastic slot in the pot and then pushed it so hard they broke it free from the solder joint. The jail bars were there with the old and still there with the new, so I'm sure it's not the shielding.

Perhaps this has been asked and answered but will bring it up.

I presume the jail bars are caused by either of the below:

video info (lack of blanking during retrace)

video info (ringing happening during trace)

non linear sweep during trace (not likely) if this was the case I would think holding the scope prob near the horz leads of the yoke should give a wave pattern that would have the ringing during the rise time, but that is just a guess.

Did you ever try putting on a blanked out screen and scoping the G1's (and may was well look at the cathodes and G2 for that matter, even though they should not have video info).

with an blanked out screen you should have no AC signal at the G1 (or cathodes and G2 for that matter).

You should adjust the brightness and contrast on the blank screen to make the jail bars as bad as possible.


This should be done with a blank screen image being fed to the tuner so you can see the horz sync pulse (the blanking period) followed by a burst pulse.

If there in no AC signal between H sync pulses, then is seems it would HAVE to be insufficent blanking during retrace.

If that's the case I would still be hung up on how you have the brightness/contrast/screen drives setup. I think this is the same set that you said you could not get the CRT setup done when using the described SAMs method using the setup switch and G2 adjustments.

Perhaps this has been asked and answered but will bring it up.

I presume the jail bars are caused by either of the below:

video info (lack of blanking during retrace)

video info (ringing happening during trace)

non linear sweep during trace (not likely) if this was the case I would think holding the scope prob near the horz leads of the yoke should give a wave pattern that would have the ringing during the rise time, but that is just a guess.

Did you ever try putting on a blanked out screen and scoping the G1's (and may was well look at the cathodes and G2 for that matter, even though they should not have video info).

with an blanked out screen you should have no AC signal at the G1 (or cathodes and G2 for that matter).

You should adjust the brightness and contrast on the blank screen to make the jail bars as bad as possible.


This should be done with a blank screen image being fed to the tuner so you can see the horz sync pulse (the blanking period) followed by a burst pulse.

If there in no AC signal between H sync pulses, then is seems it would HAVE to be insufficent blanking during retrace.

If that's the case I would still be hung up on how you have the brightness/contrast/screen drives setup. I think this is the same set that you said you could not get the CRT setup done when using the described SAMs method using the setup switch and G2 adjustments.

You are correct. I am unable to get any drive other than blue to produce a faint line in setup. The other two don't show up at all. Well, they might if I could completely black out my room (guess I could try it at night). Still, if the line doesn't show up in a dim room, that not normal, right?

I had to pull the IF and adjust the G2s for a dim raster. Checking the voltages, they are within the range noted by Sams.

My new pattern generator allows me to pretty much blank everything out and just leave the jail bars (IQW off, chroma off and luminance off).

So I should pull the socket back a bit, put the probe's j-hook on each of the G1s and the cathodes. My scope is not designed for the voltage found on the G2s and I don't have a HV probe.

As for the ringing around the yoke, I see a ringing type pattern in that whole area, especially the focus wire (just having the probe near, not touching). I don't know if it's actual ringing or just a normal electrical field the scope is picking up. I'm attaching a pic of what the scope sees in the general HV area and around the yoke wires, focus wire and FB.

the G2 is prob around 800v max, at 10x and if you have a 10v setting on the scope you should be able to read it, besides you will have the scope on AC so it should not matter. Start with 10x 10v then AC and then switch to lower and lower voltage settings on scope, that covers the G2, but there really should be no AC here anyway. Same goes for the cathodes.

G1 is where the video signal shows up (luma and chroma on this set) again start with 10x on 10v AC and work down the voltage, looking for a wave form pattern between Horz blanking pulses, the dark screen should be still a fair amount below the max amplitude found on the horz blanking pulse.

Generally speaking the horz video pulse should blank out the signal during flyback time, it is aided by the pulse from the fly that is fed to that blanking transistor (talking horz now) to furter cut off the CRT.


Zeno, any possibility this could be an AGC issue? maybe limiting the blacker that black region?

Tin Can give us a good shot of the CRT with the jail bars again with a transmitted blank screen. Adj the contrast and brightness to max and min the effect, then lets see some actual images using those same max and min settings.



the question that needs to be figured is
jail bars in video or sweep.


the below I really don't think is the issue, I still want to think its a blanking issue, not enough cut off to the CRT during flyback) but here it is:
as far as the horz sweep, you want to look at the rise time not the ringing after the drop off (that is a given and will always be there to some extent).

can you see the horz rise by holding the prob right up near one of the horz defection coil leads? if so look at the rise, is in smooth or rippled, the ringing you are showing in that other pic is I presume the ringing after the sudden drop off, not during the trace part of the scan. You want to see if the trace part is smooth.

...

the G2 is prob around 800v max, at 10x and if you have a 10v setting on the scope you should be able to read it, besides you will have the scope on AC so it should not matter. Start with 10x 10v then AC and then switch to lower and lower voltage settings on scope, that covers the G2, but there really should be no AC here anyway. Same goes for the cathodes.

G1 is where the video signal shows up (luma and chroma on this set) again start with 10x on 10v AC and work down the voltage, looking for a wave form pattern between Horz blanking pulses, the dark screen should be still a fair amount below the max amplitude found on the horz blanking pulse.

Generally speaking the horz video pulse should blank out the signal during flyback time, it is aided by the pulse from the fly that is fed to that blanking transistor (talking horz now) to furter cut off the CRT.


Zeno, any possibility this could be an AGC issue? maybe limiting the blacker that black region?

Tin Can give us a good shot of the CRT with the jail bars again with a transmitted blank screen. Adj the contrast and brightness to max and min the effect, then lets see some actual images using those same max and min settings.



the question that needs to be figured is
jail bars in video or sweep.


the below I really don't think is the issue, I still want to think its a blanking issue, not enough cut off to the CRT during flyback) but here it is:
as far as the horz sweep, you want to look at the rise time not the ringing after the drop off (that is a given and will always be there to some extent).

can you see the horz rise by holding the prob right up near one of the horz defection coil leads? if so look at the rise, is in smooth or rippled, the ringing you are showing in that other pic is I presume the ringing after the sudden drop off, not during the trace part of the scan. You want to see if the trace part is smooth.

Okay, give me about an hour and I'll provide the images you requested.

Also, the max voltage on mine is 5V/div. The manual says it +/- 250V DC plus peak AC at 20Kilohertz. I don't think I should go near the G2s, do you?

I think you meant to say that the cathodes are where the video signal is applied to the CRT. G1, and G2 should have DC on them.

oops right thanks Andy.

Tin Can just do the check on the cathodes with the scope for now with the transmitted blank screen, use the horz rate, AC, make sure you can see the entire trace including two horz sync pulses.

after that the G1 and the G2, If you scope works like mine the AC setting should allow you to look at the G2 (using 10x and 5v would be 50v per div) since it should see very little AC at all, assuming the filter caps are ok on those supplies (the 250 and the 870, both derived in the horz circuit). If you want you could start by turning the screen pots fully CCW that would place the G2 at the lowest DC voltage of 250v (but again it should not matter as there should be NO ac anyway).

oops right thanks Andy.

Tin Can just do the check on the cathodes with the scope for now with the transmitted blank screen, use the horz rate, AC, make sure you can see the entire trace including two horz sync pulses.

after that the G1 and the G2, If you scope works like mine the AC setting should allow you to look at the G2 (using 10x and 5v would be 50v per div) since it should see very little AC at all, assuming the filter caps are ok on those supplies (the 250 and the 870, both derived in the horz circuit). If you want you could start by turning the screen pots fully CCW that would place the G2 at the lowest DC voltage of 250v (but again it should not matter as there should be NO ac anyway).

Okay, I know the G2s are in the bottom right of this schematic and feed the higher voltage (540 - 640V) pins on the CRT. Are the G1s the ones in the 140V range and the cathodes in the 36V range? If so, should I test at the pins of the CRT or find a spot on the chassis?

You'll also note the test points on the schematic that feed the taps, etc. Are those ones I should scope? And if so, do they take the place of doing so on the CRT pins for those?

Here are a few pics. First one is contrast down and brightness up. Second is brightness and contrast up. Third is a question as to whether I need to redo purity of if it needs a good degauss.

wow looks pretty good in the second pic, how does that look with regular content? can you adj for good contrast and reasonable brightness and not have jail bars? Now I wonder if there is a problem or are you just asking too much of it. Remember jail bar exist due to lack of complete blanking in retrace, if the CRT bias setups (contrast/brighness/G2) are pushed to an extreme I would not be surprised that they could show thru.

as far as were to hook up, I would pull the CRT socket back a tad and use the clip on style scope probe.

you have a very slight purity issue, I would leave it alone as rarely will you notice that with regular viewing.

my magnavox bicentennial set has slight jailbars.only on a direct tv receiver.on my zenith converter and dvd player,no jailbars.at approx 50 percent brightness and contrast,no jailbars.these sets werent built for modern day receivers,etc.i adjust mine to a level where they are not noticeable or gone.purity is almost a non issue on your zenith.now post pics of screen with images!we want to see that glorious zenith picture.waited wayyyyyyy too long!

wow looks pretty good in the second pic, how does that look with regular content? can you adj for good contrast and reasonable brightness and not have jail bars? Now I wonder if there is a problem or are you just asking too much of it. Remember jail bar exist due to lack of complete blanking in retrace, if the CRT bias setups (contrast/brighness/G2) are pushed to an extreme I would not be surprised that they could show thru.

as far as were to hook up, I would pull the CRT socket back a tad and use the clip on style scope probe.

Thing is, the second picture is full contrast AND full brightness w/massive blooming. It's definitely being overdriven. If you try to watch program content, it is way too bright and washed out. The jail bars are the most noticeable with normal levels of brightness and contrast.

I usually bring up the contrast to the point of blooming and then back it off. I then keep backing it off until the level is right for the viewing environment. I then adjust brightness up until I get decent shading in the dark areas of the picture. Sometimes I have to go back and forth between the two controls to get it right. In no way am I driving it too hard with those controls and the G2 voltages are within range.

Tomorrow will be my day for checking the cathodes, G1 and G2s.

my magnavox bicentennial set has slight jailbars.only on a direct tv receiver.on my zenith converter and dvd player,no jailbars.at approx 50 percent brightness and contrast,no jailbars.these sets werent built for modern day receivers,etc.i adjust mine to a level where they are not noticeable or gone.purity is almost a non issue on your zenith.now post pics of screen with images!we want to see that glorious zenith picture.waited wayyyyyyy too long!

Is there a trick to taking pictures of the screen? The pictures always look bad compared to the live image.

Would it help if I were to video the scoping process tomorrow? I am going to scope all the cathodes, G1s and G2s and figured I'd record the process and then put it up on youtube. It'll be my first video upload.

I just thought that it might be more helpful for all involved if they got to see how I was doing it, how the scope was set and what the waveforms looked like.

Yes video would help IMHO.

Well the video didn't work out. It was too crazy trying to change the probe to different pins and change the scope settings all while trying to video. I would have spent longer editing the video than creating it. So I just went down the line and scoped the pins in order of color.

Below are the connections and the scope's volt/div setting. They all were with a time/div of 20us.

Green
Cathode .5V/Div
G1 20V/Div
G2 10V/Div

Red
G2 2V/Div
Cathode .5V/Div
G1 20V/Div

Blue
G2 2V/Div
Cathode .2V/Div
G1 20V/Div

When you look at the green G2 waveform, compare it to the red and blue G2s. The Green waveform came out nice and clean. The Red and blue, however, is a multiple form again. I don't know why this is happening, but the red and blue from should look the same as the green.

The attached pics will be in order of above (starting with Green Cathode). The first 6 will be in this post and the next 3 will be in the next post (seems only 6 can be attached per post).

Hope this helps. If it's true there shouldn't be any AC on the G1s and G2s, what's the deal?

Remaining pics from previous post.

So nothing? No ideas? Nothing about those waveforms brings anything to mind?

Did you move the scope probe ground lead during taking this series?
[Edit: you should connect the ground lead of the probe you are using to the chassis, keep it attached at one particular point for all the measurements, and do not connect any other scope ground leads to the chassis.]

The "fat" traces could be superimposed 60 Hz hum due to intermittent probe ground (can't tell from stills, but you could verify by slowing the scope sweep to vertical rate).

In any case, there appears to be ripple on the green cathode and grid, less on red and blue. Why they should be so different doesn't make a huge amount of sense, unless it varies with the scope probe grounding, because the bars you have shown pictures of appear to be monochrome - so they should be in all three guns.

Also, in the off-screen shots with a regular picture, the bars aren't visible. Are they visible to the eye at all with a regular picture, or only with a plain black scene?

Did you move the scope probe ground lead during taking this series?
[Edit: you should connect the ground lead of the probe you are using to the chassis, keep it attached at one particular point for all the measurements, and do not connect any other scope ground leads to the chassis.]

The "fat" traces could be superimposed 60 Hz hum due to intermittent probe ground (can't tell from stills, but you could verify by slowing the scope sweep to vertical rate).

In any case, there appears to be ripple on the green cathode and grid, less on red and blue. Why they should be so different doesn't make a huge amount of sense, unless it varies with the scope probe grounding, because the bars you have shown pictures of appear to be monochrome - so they should be in all three guns.

Also, in the off-screen shots with a regular picture, the bars aren't visible. Are they visible to the eye at all with a regular picture, or only with a plain black scene?

The ground was connected to the same spot for all tests (I used the ground on the CRT socket). I will try to bring down the sweep rate and see if the waveform clears up.

The bars are most noticeable when the screen is darker like in a transition between scenes. You can see them with color screens, but only if the colors are light/pale.

I'm wondering if my 750V boost is working as designed. I haven't looked at it until today. So far all I did was check its voltage. It's 761VDC. I didn't check the AC as my DMM isn't a true RMS. I'll need to put it on the scope to see the AC. I figure I can start at the diode that steps it up and work my way to the G2 controls.

I will try to bring down the sweep rate and see if the waveform clears up.

Possibly the "fat traces" are due to a very high frequency component riding on the waveform, so increasing the sweep speed might reveal its shape. Use the internal triggering of the 'scope to see if you can trigger on the superimposed (and presumably extraneous waveform) and display it to determine what it may be. So try both higher as well as lower sweep rates.
jr

...

It's not unusual for the ground wire to act like an antenna and pick up signals from things like the flyback and yoke. It looks to me like you have ringing on all of those signals and voltages. It could be a filtering problem, but I think the ringing itself is the problem.

What voltages to you have on the 240v and 750v boost sources? If one of those is low, it could explain the lack of a bright service line, and be causing the bars.

These types of problems can be real head scratchers and often end up being the last thing you would suspect. It could even be the yoke or flyback. You might want to look for a parts donor in an ugly cabinet. A whole chassis transplant isn't a crazy idea if you value your time.

Those voltages test out as 248VDC and 761VDC. So their not on the low side.

I was hoping someone could look over the schematics I posted earlier and tell me what happens when the setup switch is activated. To me, a beginner, it looks like it does something and collapses the vertical. That's my best guess based on what I get looking over the schematics. If that's what's happening, then the lack of setup line for all but a faint blue is puzzling.

If it comes down to replacing the FB or yoke, I'll live with the bars. I don't want to get that involved. I think for the heck of it I'll look over all the caps and resistors in the 750V boost area. Could be a decoupling cap.

Those voltages test out as 248VDC and 761VDC. So their not on the low side.

I was hoping someone could look over the schematics I posted earlier and tell me what happens when the setup switch is activated. To me, a beginner, it looks like it does something and collapses the vertical. That's my best guess based on what I get looking over the schematics. If that's what's happening, then the lack of setup line for all but a faint blue is puzzling.

If it comes down to replacing the FB or yoke, I'll live with the bars. I don't want to get that involved. I think for the heck of it I'll look over all the caps and resistors in the 750V boost area. Could be a decoupling cap.
Service switch kills vertical also kills video & gives the 3 video outs a
constant voltage. On this chassis it also adds a crude blanking pulse.
If all the DC voltages are correct you should get very bright service
lines. At that point its 99% the CRT. Sometimes the CRT can look
& test good but be a little weak.
Good news ! Since I was a bench man & only did about 25 of these
sets I ran it by our old road man over a beer. He did a repair on
one once & it had the exact same jailbars. Bad news is the set was
very old & they didnt want to pay to pull the chassis. At least you
know this wasnt self induced & a real failure, possably common.
Just for kicks remove the wire from service switch that go to
jcn of R295 & R297. See if they go away.

73 Zeno:smoke:

you thinking a leaky switch Zeno?

you thinking a leaky switch Zeno?
A long shot but yes. When in service instead of video they tie in
a pulse from the FBT. Zeniths had problems with the tiny
remote/man SW & on/off buttons on this vintage getting leaky
& causing random on/off. Rare but they can get leaky & its
gonna be something strange if ever found.

I wonder if anyone here is on the old Electronix pay site ? I bet
the answers there..........

73 Zeno:smoke:

Another *very* long shot, but I gotta ask... Is the external dag coating on the CRT ok and properly grounded? Any shielding around the CRT or Yoke that is not properly grounded?

jr

Another *very* long shot, but I gotta ask... Is the external dag coating on the CRT ok and properly grounded? Any shielding around the CRT or Yoke that is not properly grounded?

jr

Okay, I don't know about the coating other than there is a small scratch from where the metal shroud around it must have touched it at one point. The metal shroud has a ground from chassis to it and two from the CRT socket connected to it. How do I go about checking for proper CRT grounding?

Service switch kills vertical also kills video & gives the 3 video outs a
constant voltage. On this chassis it also adds a crude blanking pulse.
If all the DC voltages are correct you should get very bright service
lines. At that point its 99% the CRT. Sometimes the CRT can look
& test good but be a little weak.
Good news ! Since I was a bench man & only did about 25 of these
sets I ran it by our old road man over a beer. He did a repair on
one once & it had the exact same jailbars. Bad news is the set was
very old & they didnt want to pay to pull the chassis. At least you
know this wasnt self induced & a real failure, possably common.
Just for kicks remove the wire from service switch that go to
jcn of R295 & R297. See if they go away.

73 Zeno:smoke:

Okay, Sunday is the day to disconnect the wire from the junction noted to the switch. So I am to leave it in normal mode without that lead in order to see if the switch has a bad connection and might be allowing current from that lead from the setup side to the normal side, right?

Just thought I'd post a pic of the switch. I don't know if this could cause any problems, but it looks like terminal two of the setup side of the switch is wired to ground, but also the T2 of the AGC pot is also connected to the same terminal on the setup switch. I've circled the ground side in yellow and the power side in red (the lead to be disconnected on Sunday).

Okay, I don't know about the coating other than there is a small scratch from where the metal shroud around it must have touched it at one point. The metal shroud has a ground from chassis to it and two from the CRT socket connected to it. How do I go about checking for proper CRT grounding?

So is there any connection between the shroud and the dag coating? It sounds as if the shroud and I'm guessing perhaps spark-gaps at the CRT socket are grounded to the chassis. Might want to ohm check the ground connection to make sure.

jr

Just thought I'd post a pic of the switch. I don't know if this could cause any problems, but it looks like terminal two of the setup side of the switch is wired to ground, but also the T2 of the AGC pot is also connected to the same terminal on the setup switch. I've circled the ground side in yellow and the power side in red (the lead to be disconnected on Sunday).
Its OK they are using it as a tiepoint for ground.
Yes run it in normal for the test.
The CRT dag usually grounds through a few paths. The DGS shield
has fingers on it touching the CRT, usually a spring mounted wire
across the bell under the shield, sometimes the ground straps
touch the dag. Then usually straps run from the shield to the
chassis, tuner assy, & convergence assy. If it were floating you
should hear hissing, used to happen to B&W's sometimes.

Lead dress keeps me worried here also. Be sure the CRT harness
is well away from any HV or large hoz pulses. Focus, yoke,
and the 2 HV leads. IIRC its pretty hard for that to happen on
this set.
Also bad caps may have caused it. Every S cap that opens
brings up everything from the HOT on up 10%. In the olden days
it usually stressed the divider then the F terminal of CRT
socket arcs. If a bunch of them go it starts tossing lightning
bolts like you read about ! Quite a show........
So over time things may have been under stress.

73 Zeno:smoke:

Here are a couple of pics of the CRT and the shroud w/ground leads. You can see the two from the CRT socket and the one that goes from the shroud to the chassis. If you look closely at the left side of the neck you'll see the scratches, but I don't think they went through the coating. They appear more as surface scratches.

As for the setup switch, I'm gong to use some Deoxit on it first to see if it needs a little cleaning. I figure that being in the same position for so many years and the fact it's an open design, it might be dirty/oxidized.

You should not need to spend much time on the dag connections. The dag appears intact, as do all the wires. Just look for obvious mechanical problems, and wiggle the connections a bit to see if the problem you are trying to fix shows intermittent effects.

Service switch kills vertical also kills video & gives the 3 video outs a constant voltage. On this chassis it also adds a crude blanking pulse.

So is the horizontal still there when in setup? Reason I ask is that the bars go away.

Also, don't remember if I checked the voltages on the G2s and G1s when in setup mode. Maybe that is a next move.

the bars go away cause the vert is collapsed.

The dag appears intact

I must be missing something... I don't see any external dag on the tube... is there just a little area of dag on the lower part of the tube where the grounding strap wraps under?

jr

I must be missing something... I don't see any external dag on the tube... is there just a little area of dag on the lower part of the tube where the grounding strap wraps under?

jr

Here's a pic from when I first got her and hadn't been cleaned yet. This metal shield goes all around the back side of the CRT. It had ground straps from the CRT socket and chassis on it.

So what area of the tube does the external dag cover... I am still not sure that I see it. Note the highly visible pattern here where the external dag can be clearly seen *almost* to the yoke: http://upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Crt14.jpg/717px-Crt14.jpg
jr

So what area of the tube does the external dag cover... I am still not sure that I see it. Note the highly visible pattern here where the external dag can be clearly seen *almost* to the yoke: http://upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Crt14.jpg/717px-Crt14.jpg
jr

In the picture you'll see the metal (bronze colored) shield connected with springs and other screw type adjusters/fasteners (you can see a long screw that is used to pull the sections together for a tighter fit). That's the part that in contact with the painted on DAG of the CRT and then connected to the chassis via a yellow ground connector.

The CRT shields on Zeniths of that era almost completely hide the dag. I should know I have at least two Zeniths that use that CRT shield.

The CRT shields on Zeniths of that era almost completely hide the dag.

Good enough! I have never seen one in person and thought that the HV filtering (and ringing suppression) would be really poor if it were missing from a sloppy re-build job or from somebody cleaning all that "dirty stuff" off of the CRT.

jr

The CRT shields on Zeniths of that era almost completely hide the dag. I should know I have at least two Zeniths that use that CRT shield.

thanks for this comment - made me look again, and I now see that apparently the picture shows the internal dag (?). If the external only is underneath the shield, then it is probably OK because none of the external components, labels, etc. are disturbed.

I still think the dag is a wild goose chase for anything having to do with the jail bars (isn't that the one thing we are trying to fix here?).

Need to stop shot-gunning and try to follow clues - there is a jail bar pattern in at least some of the CRT leads, and there are questions as to why some of the waveforms are fat (high frequency or low frequency superimposed?). Should be chasing down if those scope waveforms are valid and going from there.

thanks for this comment - made me look again, and I now see that apparently the picture shows the internal dag (?). If the external only is underneath the shield, then it is probably OK because none of the external components, labels, etc. are disturbed.

I still think the dag is a wild goose chase for anything having to do with the jail bars (isn't that the one thing we are trying to fix here?).

Need to stop shot-gunning and try to follow clues - there is a jail bar pattern in at least some of the CRT leads, and there are questions as to why some of the waveforms are fat (high frequency or low frequency superimposed?). Should be chasing down if those scope waveforms are valid and going from there.

I'm ready and willing to do any testing you guys come up with. I'm going to disconnect the lead for the setup side of the setup switch to see if there's some kind of issue in the switch. It seems to be a pretty basic open design switch, so I cleaned it with Deoxit. That didn't help as I still have the bars and I still can't get a setup line from the red or green and only a faint line from the blue.

Never mind. I missed a couple of points of connection, so I'll have to start over. I thought I was able to delete posts, but I don't see how.

Okay, spent the better part of today looking into why the setup doesn't produce a line. This is what I found out, but not why or how to fix.....

The G1 voltage controls brightness and the higher the voltage, the dimmer the output. The voltage should be around 142V for normal and actually measures out around 147 - 150V. That's not too bad. It's when the setup mode is entered that things change. The voltage of the G1s goes up to 190V and that must be why I can't see the lines when adjusting the G2. 190V is making it too dim to see.

Now why the voltage goes up that high is beyond me. I looked over the schematics and see an 18K and a 1.8K resistor on the setup side of the switch and am not sure if one of those (or a combination of both) could account for the voltage difference.

Okay, spent the better part of today looking into why the setup doesn't produce a line. This is what I found out, but not why or how to fix.....

The G1 voltage controls brightness and the higher the voltage, the dimmer the output. The voltage should be around 142V for normal and actually measures out around 147 - 150V. That's not too bad. It's when the setup mode is entered that things change. The voltage of the G1s goes up to 190V and that must be why I can't see the lines when adjusting the G2. 190V is making it too dim to see.

Now why the voltage goes up that high is beyond me. I looked over the schematics and see an 18K and a 1.8K resistor on the setup side of the switch and am not sure if one of those (or a combination of both) could account for the voltage difference.

Something's wrong with your measurements - either you are not measuring G1, or something else is going on.

G1 voltage higher = more brightness. Cathode (K) voltage higher = less brightness. It's mainly the difference between cathode and G1 that controls beam current, so you have to measure both to figure out what's happening.

These voltages *should* change to a predetermined value when you go to the setup mode, so that you can set the G2s for proper cutoff; then when you go to normal, the signals on the cathodes and G1's will produce the right colors.

Something's wrong with your measurements - either you are not measuring G1, or something else is going on.

G1 voltage higher = more brightness. Cathode (K) voltage higher = less brightness. It's mainly the difference between cathode and G1 that controls beam current, so you have to measure both to figure out what's happening.

These voltages *should* change to a predetermined value when you go to the setup mode, so that you can set the G2s for proper cutoff; then when you go to normal, the signals on the cathodes and G1's will produce the right colors.

This is what I got out of a book on CRTs.

"The control grid (G1) controls the brightness of the CRT. It is generally
placed directly on top of the cathode. If there is no voltage on G1, the
electrons can flow freely from the cathode. If there is some negative voltage
on G1, the electrons from the cathode are repelled somewhat, and the screen
appears darker. The greater the voltage on G1, the darker the screen becomes, because more electrons reaching the screen equals a brighter image, and less electrons hitting the screen equals less brightness."

I'm attaching the CRT section of the schematic. If I have the G1 information incorrect, I need to know. My understanding is pins 2, 11 and 6 are the G1s. I'm also attaching a pic of a chart from a CRT tester manual.

Just made a discovery. As most will recall, I can't get the setup line to show. That was until today. I managed to get the line to show, but under conditions outside of the normal setup procedure.

I set the switch into setup mode and there was no line. I then pulled the red tap off, completely and a bright red line showed up. I then did the same to the blue and green and got a bright whitish line in the center of the screen. Now outside of setup, the screen is way too dark to be useful. I then checked the voltage on the blue video output driver (yellow/blue wire on crt #11). It is 188 - 190V in setup with the tap in any of the HI, MED or Lo position. However, when I remove the tap connection it drops down to 132V and that when a very bright blue line shows up.

The Sams says to do this with the taps on "HI", so something must be off to keep the line from showing up with the haps connected.

So, does this new information give anyone any ideas as to what the problem might be? Is there something I should be measuring while the taps are disconnected? The collectors of the video output transistors?

Okay, another update and question.

Since finding out that disconnecting the screen tap wires from the taps allowed the setup line to appear, I decided to check voltages. I found something I don't understand, and therefore, don't know if it's normal.

I am attaching a pic from the schematics for the video outputs and screen taps. In it you'll notice that the screen taps get voltage from the collector and the 240V boost through a series of resistors. Those are the supply connections. Then there is the tap wire that you move from tap to tap. That wire receives the voltage and it is connected with a resistor to the CRT socket. That lead has no power indicated on the schematics unless it's connected to one of the taps (hi, med or lo). However, when I disconnect the lead and check it, it has 133V on it. If I disconnect the CRT socket and run the set, the lead has 0V. It's the same for all three colors. Is that normal? Should there be voltage on it from the CRT side? On all three colors?

Maybe I'm not fully understanding how this section is designed to work.

This is what I got out of a book on CRTs.

"The control grid (G1) controls the brightness of the CRT. It is generally
placed directly on top of the cathode. If there is no voltage on G1, the
electrons can flow freely from the cathode. If there is some negative voltage
on G1, the electrons from the cathode are repelled somewhat, and the screen
appears darker. The greater the voltage on G1, the darker the screen becomes, because more electrons reaching the screen equals a brighter image, and less electrons hitting the screen equals less brightness."


I believe that the above quote is coinfusing, IMHO it should read: " The greater the NEGATIVE voltage on G1 the darker the screen becomes"

jr

I believe that the above quote is coinfusing, IMHO it should read: " The greater the NEGATIVE voltage on G1 the darker the screen becomes"

jr

Yes. Hate this sloppy kind of writing, where it can only be understood by somebody who already knows the subject. Properly stated to avoid confusion, it would be "more negative," and not "greater" when referring to a negative quantity.

Ringing,assuming the damping resistor across the line linearity coil is ok,is often caused by the bypass cap in the video output stages being o/c,value usually 10-33uf 250v,make sure,as with everything you don't use chinese sxxt as replacements