Picture streaking

[old_tv_nut]

I am getting more curious too. What do you see if you put the scope on the B+ that feeds the vertical? Does the vertical section get power from the horizontal some way, like from B+ boost? (Trying to guess how extreme brightness could affect the vertical.)

[David Roper]

FWIW I've experienced this with a 16" metal cone tube.

[Einar72]

Looks like the whole vertical section runs off the boosted B+ supply. I still vote for video leaking into the vertical sync circuits. If the boosted B+ was unstable, I'd expect to see non-linear horizontal sweep, plus trace dimming and blooming as well. I'd take that scope and look at the sync signal at R401. Also, look at the grid of the 6S4 and see if tou have a decent sawtooth waveform there.

If you don't have a clean ramp-shaped signal, I'm gonna push you out on a limb and (with others agreeing, it's not my TV here) suggest lifting one end of R 401 and see if you can get the vertical oscilator to sit still long enough to see if that clears up the distorted sweep.

One more thing. Did you REALLY check your work when you were done? It just takes one wrong-value part or one wrong connection to mess it all up. Just for the heck of it, recheck the vertical and sync circuit wiring really close. Good luck!

[W4rtc]

Well I think I found the problem, at least on my set. In restoring the set I put the retrace line mod in to remove the retrace lines. Well I removed the mod and now the picture is o k at any setting of the brightness or contrast setting. I put the mod back in and the pinching of the scanning lines came back. On my set I dont really need the mod as the retrace line are not there unless I turn the contrast way down. So I will most likely leave the mod out. Or I may try some different size components. But for now I have a beautiful picture. Thanks for all the help. I do need a alignment tho guess i will have to ger me a sweep generator. OH well. Thanks
Joe

[old_tv_nut]

Could you post a partial schematic with/without the retrace mod? I would like to understand this for future reference.

[W4rtc]

Hi OTN
Here is the best I can do I am not too good with making computer drawings so I did it by hand hope this helps.
Joe

[old_tv_nut]

Hmmm - maybe the peak whites are drawing grid current on the CRT, and affecting the vertical grid voltage of the vertical output? A bigger value for C310 might change things, but not fix them. Too big a value would filter out the pulse that is intended to blank the retrace lines.

If you could find a negative vertical retrace pulse somewhere else, it might work and not affect the vertical sweep.

Another thing to try would be some resistance in series with the added .05 capacitor.

[W4rtc]

Hi
Well I replaced the .05 cap with a 900 mmf in the mod and the retrace lines are gone and the picture is great. I still get a small amount of " pinching with contrast all the way up" but 100% better with the change. I watched some of the Super Bowl and the picture was very good.
Joe

[old_tv_nut]

Glad you fixed it. It would be interesting to know what the pulse on the CRT grid looks like now. Reducing the cap should have reduced both the pulse amplitude and the feedback to the vertical about 50 times.

[Tom Albrecht]

Originally Posted by old_tv_nut

Hmmm - maybe the peak whites are drawing grid current on the CRT, and affecting the vertical grid voltage of the vertical output?

Hey -- I think you guys are on to something here! I've noticed that both the brightness and the contrast affect this bunching effect in sets that have it. Grid current in the CRT would indeed correlate to that. I'll have to put one of my sets that show this problem on the bench and go after it when I get a chance. I wonder if I have created this problem by adding my own blanking circuits to certain sets?

[W4rtc]

O K I had to take the mod to eliminate the retrace lines out. I tried many different combinations of caps and resisters, with any combination of caps and resisters it still had streaking. On the dark scenes the streaking was very bad, but take the mod out and it was o k. Just putting the resister in the mod and not the cap the streaks were there, and I tried many sizes of resistance.
Joe