Possible screwed ST-V board, or repairable?

[system11]

Because most don't try to self regulate, with an arcade PSU there's less danger of oversupply and resulting damage.

Can you explain what you mean by this? That is, do you mean that it's essentially a transformer+rectifier+rheostat or similar without even a linear regulator, or what?

Gosh that's an old quote. It was my understanding that some PC supplies try to maintain the voltage at 5v themselves rather than being adjustable. You don't generally want power supplies to do that, because it's better to find and resolve the drop than it is to simply pump more power out - take a look at the damage Atari AR-IIs can cause, which have a 5v return line.