Thanks for the replies!
I noticed the monitor had flickering on the bottom or top fourth sometimes, so I'm hoping it's the monitor. Bought one of those DB15- to VGA adapters with DIP switches and will buy a VGA CRT (much easier to find) if it turns out it in fact is the monitor that has the...
I recently got a Quadra 650 and I'm super happy with it, but either the Quadra's PSU or the monitor's (an AppleVision that wobbles a bit at the top and bottom) seem to be tripping my home's circuit breakers, even when they're off. They're both plugged into sockets, I don't have the pass-through...