I have one issue left on a resurrected LAH that I just can't solve. Immediately upon powering up, the knocker coil locks on. i replaced the associated transistor and it has not remedied the problem. I noticed that the associated flashers with that circuit are also locking on so I disconnected the knocker to diagnose further.

I discovered that when any flasher in the game fires, the 3 in the knocker circuit lock on and will remain locked on until any coil is activated. Then they will go out. When the flashers are locked on, the knocker coil will de energize. So it looks like the flashers or the knocker coil will lock on based on whether a flasher or coil has previously fired.

I have replaced every IC in the circuit for the flashers as well as the ram and the EPROM and nothing fixes it. The problem is definitely on the MPU board because I can replace it with a known good board and it works perfectly. It sounds like a crapped out relay to me but isn't the relay associated with this on the PPB?

Anyway, I did take a short video. Don't know how helpful it'll be but I'm out of ideas and any help would be greatly appreciated

The predrive transistor tests good, but maybe that's bad anyway? I guess I'll try that. I'm all out of stuff to change on the MPU besides that.

Well, I replaced the predrive transistor as well with no luck. I know I have a short to ground on the board somewhere but can't locate it.

Thanks for the offer, Jeff but I'd rather do the work myself. I enjoy the work. I've just never encountered this problem before.

Hawk007, i'll take a look at the cap, thanks.

The schematic for DE aren't as clear to me as the ones for the WPC games. I changed the only PIA that is in the part of the circuit for the coils/flashers. Could a fault in another cause this problem?

I thought about this but replacing the MPU with a known working one solved the issue. The issue is definitely on the MPU board.