Sync symptoms

[W9RAN]

Thanks Dave and Eric. Here's what I've found so far:

I'd replaced C11, and the AGC seems to be working OK, going from -.4 volts with no signal to -2.4 volts with. Changing the AGC switch only causes it to vary by .1 volt or so.

I've injected composite video in to test point "C" and get the same symptoms. So this at least should eliminate the RF, IF, and AGC circuits.

I was optimistic after seeing "component cooler" on the Radio Shack catalog that they might have it in the store, but to paraphrase the Eagles, the manager told me in essence that they "haven't had that spirit here since 1969". So I'll have to order a can I guess. In the interim I tried using an air compressor, and proved that indeed I could restore proper operation by cooling *something*, but wasn't able to pinpoint which component. But it was in the vicinity of the 6AW8, so I'm going to substitute that.

I'm also wondering if it might be a mechanical issue like a tube socket pin that warps open when hot. I've had trouble with poor connections on this and the horiz. osc. tube - to the point where filament voltage is lost, despite cleaning and trying to tighten up the sockets.

Based on my radio repair experience I tend to look at a capacitors function in the circuit and replace those where it makes sense in most cases. But you're right Eric, this is one where if I end up pulling the PC board out, I'll do 'em all.

Anyhow - thanks again, and I'm sure I'll get to the bottom of this. I remember modifying old TVs in the 70s for use with early home computers and should have remembered the composite video idea.

Bob