New Project - RCA 8PT

[maxhifi]

Thanks guys!

Removing the antennas from the rear strongly improved the picture quality. They have an internal mechanism which disconnects the antennas themselves when they are fully retracted, but it wasn't working, which allowed a lot of interference to get into the TV. Removing them and adding a terminal strip made a big difference. Now I am getting very sharp focus and can see all the scan lines.

I've noticed a new problem, a bit more subtle, There's vertical stripes on the left side of the screen. At first I thought it was screen burn, or gas in the picture tube but when you turn the contrast all the way down, and brightness all the way up to get a full raster, the horizontal hold control will shift the stripes back and forth. Attached are a couple pictures. I still haven't restuffed the can filter cap, but all other paper and electrolytic caps have been replaced.

[doogie812]

Check the filter cap for the G2. Doogie

[maxhifi]

You mean G2 of the CRT ?

I think this is a 5uf cap, part of filter can. Will try this tonight.

[doogie812]

It is probably a 0.1 – 0.5 mfd cap. At between 400 – 1000 vdc. It will not be a can. Lookup up your CRT type number on Google and follow the wire back to the chassis and find the first cap to ground. Doogie

[maxhifi]

Ah.. in that case I would have already changed it. Will verify that the value is correct.
Schematic says G2 not tied to ground through a cap?

[doogie812]

That could be true. Rectifiers were very expensive in the old days. Check caps in the yoke circuit. Just because you replaced them does not mean there good. Do you have an ESR meter? Good luck. Doogie

[doogie812]

It could be a dynamic thing.

[maxhifi]

Rebuilt filter capacitor can. First one I've ever done, it was a lot easier than I was expecting. No impact on this problem, but now all electrolytics are new.

Attached is the schematic so you can see what I mean about G2

[Eric H]

Looks like ringing in the Damper circuit, have you tried adjusting the horizontal drive coil or the width?

[maxhifi]

Just for kicks tried subbing the 6CG7, 6BQ6 and damper one by one, to no effect - all were good.

Horizontal drive doesn't seem to do much at all. Width I need to find a more appropriate screwdriver to adjust... it's got a slot in the end of a long threaded shaft, and all of my miniature screwdrivers seem to immediately slip out of the slot.

[maxhifi]

Finally got some time with the TV.
Drive/width don't do anything for the vertical bars, aside from move them around a bit. It's a shame, the picture is otherwise nearly perfect.

[Eric H]

You might try a different Damper or Horiz Output tube, sometimes a set can be fussy about which tube works better even if they are good.

[maxhifi]

Nope, not a difference. Have tried 3 different of each, and a couple 6CG7s too. I think I'm going to have to start checking resistors, etc.

[Eric H]

Ah yes, I looked back through this thread and see you did already do that.

This is one of the more aggravating problems I run into on old sets, probably something out of spec, a resistor seems likely at this point.

There are a couple of caps and resistors inside the yoke but the caps are likely Mica and unlikely (but not impossible) to be bad, the resistors might be however.

[maxhifi]

I was pretty careful to do neat work, only replaced about 8 or 10 caps in a sitting, tried to put the new caps in exactly the same place as the old ones, but I may have moved something, it's not totally out of the question.

Is it reasonable to think the problem of vertical stripes is more likely in the horizontal than the vertical section? Right now is a bit late to get the TV on the bench, but over the next few days I plan to give it some time. Problem is fairly subtle, but for sure want to get it worked out before I put the TV upstairs and into regular service.