Put them in test mode and see if there are any RAM issues.
My BattleZone played blind when I had a bad RAM on it.
Second, check the fuses on the chassis... with a multimeter... don't just eyeball them.
If there are any blown fuses, and they pop again after you replace them... the first things I would check then are the can transistors on the frame for the monitors. Just check them to make sure the can isn't shorted to ground. If you find one that is shorted, it may still be good. Loosen the screws holding them down and pull them back a little from the frame and check again. If they're not grounded when you've pulled them back, then you have some bad insulators under them. Do NOT run them like that. You can replace those insulators (temporary) with a piece of those glad oven bags (I know, I know... it worked for me). If they're still shorted to ground, then you'll have to replace whichever one is (I'd probably just go ahead and do a full rebuild on them if I were you).
Minus 1 vector monitor so far, that's fixed pretty much all of my issues.