Still Having RCA 8TS30 Issues

[Electronic M]

How strong is the vertical lock? Is it just 5 degrees or something more healthy like 1/4 turn.

Sync issues can be caused by 2 things, sync separator issues, and sweep oscillator issues. If vertical lock is weak too it indicates that the sync separator is bad or marginal. And a marginal sync input won't help the horizontal if it too is marginal. Also it's good to consider every component after the H and V sync split part of the osc circuit it feeds and scrutinize those carefully too.

Also the 630 chassis family sets lack AGC so it is possible to have contrast (which in these sets is more accurately called a manual IF and tuner gain control) set so high that the sync pulse gets clipped off at the video detector from signal overload... that's another thing to watch out for that can mess up sync.