OP

Quoted from newmantjn:

So I hauled all my boards out to Clays last night and stuck them on his system one test fixture - a game he mounted on a flat surface. It has all the coils etc.
All the boards tested good. The PS zener CR21 got a bit hot, but it it delivering the voltage it needs to.
I installed everything back in my game. No change.
Summary:
Game doesn't start. Game over relay won't pull in when you start a game. Outhole won't kick out. In lamp test mode, the kings bank fires. In coil test mode, nothing fires. I'm driving myself nuts, so I felt best to hone in on the Q relay and see if I could figure this one thing out. Should be easy, right?
I can't seem to get a decent reading on the coil resistance on the Q relay. It reads open, but I think this is a red herring - or I'm a moron. Or as I shouted earlier today - "The laws of physics don't apply in my garage."
Next, I unplugged the driver board. Then I jumped the Q relay back to the rectifier. It pulled in. Then I verified the colors and continuity on the edge connector for the Q relay. Next, I plugged the driver board back in and grounded the transistor. The Q relay pulled in.
Next, I turned the game on and observed the Q relay. I pulled in immediately. (??) Then, as soon as I pushed the credit button to start a game, it let go!! Out of sheer desperation, I swapped out the diode on the Q relay. It tested OK when I pulled it out, and, of course, nothing changed when I put a new one in.
I had another "known good" driver board, and it was roughly as schizophrenic. I don't remember if the Q relay pulled in right away or not.
This game more or less worked a two weeks ago. I've never been this frustrated with a pinball in my life.