TV-37 vertical hum?

[Tom Albrecht]

I agree that if you see the disturbance on the vertical deflection waveform, then direct magnetic influence on the CRT is not the problem. In cases where I have seen magnetic coupling from wiring, there is a cutout in the chassis to accommodate part of the CRT bell which exposes it to the under chassis wiring. I believe the specific case where I saw that problem was a Sentinel 400TV.

Thinking about the chassis and CRT mounting in a TV-37, there should not be any wiring exposed to the CRT.

If you’ve checked the power supplies and found no ripple that should be causing a problem, let me bring up one other semi-obscure problem that can cause this: The TV-37 has an aluminum chassis, and over time the riveted ground connections develop some resistance. Sometimes you need to hardwire a soldered ground wire between most or all of the ground connections on the chassis to fix the problem. In particular make sure the filter cap grounds are hardwired to this new ground wiring. The problems you can get from these bad ground connections are a little hard to predict, but AC hum getting into things is certainly a possibility.

I know you’re quite experienced, so that’s why I’m bringing up these less obvious causes of this kind of problem.