Did you recently shop out your game or take the boards out? It's possible you have something plugged in wrong under the playfield or at a connector and that's causing incorrect voltage to be sent where it's not supposed to go.

Not that I've ever done something like that myself.

That's one way to do it without fixing the original problem!

You're doing a great job trying to find the source of the problem. There has to be some stray voltage getting in your line from something on that board, and it's confirmed by your voltage measurements and the fact that you're blowing the fuses.

Take a really close look at the entire path of the circuit(s) in question. Something as small as a tiny piece of misplaced solder can cause this type of behavior.

According to what the guy at Super Auctions told me, it's always just a fuse.