Drilled the coin door lock, opened the top, made sure everything was clear and connected... things looked ok so I plugged it in, turned it on and pulled the interlock switch all the way out on the open coin door... zing!
The reason they thought it was 'non-working' was because the interlock switch on the coin door was mis-aligned and when you close the door, it closed the switch but not enough to set it "on". Basically the switch was stopping it from powering up. They never saw it running because they didn't have the key to open the door.
Realigned the switch so it set properly with the door closed and it works perfectly. Even the coin lights work. The monitor looks great too.
That's even better than a blown fuse fixing a game!