[Adam]

I haven't had time to work on TVs in months. I got stuck on this problem with this set back in December, and haven't had time to get back to it until now.

The vertical will only sync if I feed the tv with a weak signal. If the signal is strong enough for a clear picture, no snow, it won't sync.

First of all, I would think this has to be a problem with the sync separator, not the vert oscillator. I took voltage readings, and found voltages were a little high pretty much everywhere in the set. (Probably because I replaced the selenium rectifiers with 1N4007 diodes) I put dropping resistors in the power supply, but this made no difference to my sync problem, and gave off tons of heat, so I'll probably leave them out in the end.

Secondly, I tested each component individually in the sync separator circuits. Nothing tested more than 20% off from what it should be. But I eventually replaced all the resistors and capacitors, and tried several different tubes anyway, with no positive results.

Eventually, I figured if too strong of a video signal was upsetting the sync, then too much of the video signal was getting into the sync separator, so I increased the value of the capacitor I circled in the schematic I attached below from 10pf to 130pf (attaching a 120pf mica cap in parallel). I tried several different values, this worked best. The scope pictures show first what is going into the grid of the sync clipper tube, and second the output of the sync separator into the vertical oscillator, both with and without the extra capacitor. I labeled on the schematic exactly where I connected the scope probe.

Now this extra capacitor fixes my problem, the vert sync is very strong with it in there, independent of the strength of the signal the set receives. (Both with or without the extra dropping resistors in the power supply) I'm getting ready to just put it back together with the larger capacitor in there, but I'm still wondering why I needed it in the first place?