Are these things I should consider bad

[andy]

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[TinCanAlley]

Originally Posted by andy

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.

[TinCanAlley]

Originally Posted by andy

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?

[TinCanAlley]

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.

[TinCanAlley]

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.

[N2IXK]

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.

[TinCanAlley]

Originally Posted by N2IXK

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?

[TinCanAlley]

Originally Posted by N2IXK

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.

[TinCanAlley]

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?

[zeno]

Originally Posted by TinCanAlley

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