Old CRT goes to jagged diagonal on old motherboard and PSU

[loninapleton]

I have a lot of old gear. But this intermittent problem looks like it's just some part gone bad. However I don't know which one:I've swapped out poiwer supply for a different one, reninserted mem stick (only one on this very old motherboard) and jiggled various connections.

The CRT going jagged and freezing seems random and not related the the monitor itself. And the computer continues to function- I had overnight HD Low Level Format that completed.

The motherboard has onboard video. I have no compatible
video card to test.

Could this be a connection at the PSU plug that goes to the
motherboard? I've considered looking at the motherboard connection and refreshing the solder joint but my soldering might do more harm than good.