[old_tv_nut]

Not a Zenith design. Zenith bought Heath in 1979. There were some later Heathkits based on Zenith chassis, I believe, but they involved much less construction and soldering and were more snap-together if I recall correctly.

The fact that the dot pattern is straight shows that this is not a power supply hum problem. It is probably a reaction to the VCR signal horizontal jump at the head switching time. Either something has failed in the horizontal AFC or more likely this set has an earlier design of the horizontal AFC filter section that predated VCRs. Another possibility is that there is a switch setting for a shorter AFC time constant, although I don't recall if there was one on the Heathkit I built in 1975.

Play a DVD or digital converter box into the set instead of the VCR and verify that the wave goes away.