Resoldering that joint didn't work, it still shuts down. I did manage
to identify the vertical IC, but there's not a bad joint anywhere near
it.

So, what can cause the vertical signal to just randomly stop? I'm not
sure what else to try here.


Some bad joints are hard to spot, I would try prodding the board with an
insulated stick with the set on. I would also look at the power supply.

If it is determined that a solder joint isn't the problem, the next thing I
would do is check for marginal capacitors.