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More clues: I pulled the bank of vertical adjustment pots, and they measure good out of circuit -- the vertical linearity pot tops out around 1.7m ohm. In circuit, it reads around 520. I don't read any continuity between its traces with it pulled, which suggests the current is finding an easier path to ground.
I swapped C208 with one from an S-3 parts chassis. The one in my problem set had some fluctuating readings on my meter, and the replacement didn't.
The way these sets were modified, the antenna screw terminals were repurposed to carry audio and video. I noticed that the solder on the terminals inside the set had failed, and the wires were flopping around the terminal holes. Resoldered those.
I'm not sure if it was the cap or terminals, but the problem has lessened. It still doesn't seem like it properly locks sync, but it drifts a lot less.
I think the next things I'll try are swapping C201 and C210, both those are close to the problem and one end connects to ground, so current could be escaping that way.
The other thing I'm wondering about is the trapezoid-indicated +135v supply, which is connected to one side of the vertical linearity pot. I observed that R403 (130 ohm, 5W ceramic resistor) gets very hot, and that's on the +135v line. It measures good on my meter, though, I suppose a 5W resistor is going to get hot. It's not glowing, just uncomfortably hot to the touch.
Any other suggestions for me?
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