Interesting thought. I'm in the process of following the pulses back up the chain, so I'll keep an eye out. Maybe there's a leaky mica cap somewhere. I was looking at the sync pulses earlier, but they were a little non-sensical; I suspect I need to trigger off the vertical instead of the horizontal for them to make sense otherwise I see what I think are artifacts of the blanking period in between. Might be tricky with just a 2 channel scope but if I can get the EXT trigger to work it should be doable.
Should comment that this video was with the oscillator free-running (no video input) but if there is an input it still behaves the same. I'd be less surprised if it did this only with input as it could be explained by the sync circuits pulling the oscillator into phase.
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