I just got my parent's old Disco Fever pin from 1978. Worked great when I was a kid, but it's been ignored for quite a while now. It's behavior upon turning it on is intermittent. Note that I have replaced all fuses on the backboard.

Sometimes it enters Game Over mode correctly and will actually accept credits. None of the solenoids fire when you try to play it, and manually hitting any of the targets may or may not record a score. Sometimes in this mode you can actually add another player when hitting one of the rollovers at the top of the playfield. And sometimes the tilt will just go off for no obvious reason. When the system behaves like this the CPU diagnostic indicates that everything is correct. I can sometimes get the manual diagnostics to run in this mode (e.g. lamp test, etc.), but not always.

In other cases you will get no useful behavior upon turning the system on. In this case, both LEDs are lit on the CPU board and pressing the diagnostic does nothing. This makes me think the CPU board is flaky.

I have looked at this page (http://www.pinwiki.com/wiki/index.php?title=Williams_System_3_-_7), but haven't yet gone through any of the diagnostic steps.

Any help would be appreciated.

Thanks.