When I press the start button, the scores reset but the flippers don't work and the ball doesn't eject. There is a loud buzzing coming from the coil that controls the ball count. It appears to be stuck on and I'm not sure why. I can manually rotate the back of the unit to game over. If it's related, the alternating light function was not working well before this happened. The lights would briefly alternate but then go back to the right outhole lit position. Everything else was working correctly. I don't have a schematic.

Shipping would be a killer!

Yeah, it's a '73 Gottlieb King Pin.

Thank you, I think you're right about the ball trough switch. The ball was actually getting stuck in the trough (I thought I'd forgotten to put the ball back and put another ball in which ejected the first ball) When I cleared the trough, no more buzzing. I appreciate your help. Do you know what might be causing the alternating light issue? The alternating relay appears fine, I was thinking it's the mini stepper in the backbox.

No, I don't have a schematic. The ball count's working fine now...just have to fine tune that mini stepper to get the alternating feature right.

The alternating lights function some of the time, so I'll try adjusting the mini stepper. Q seems to be activating.