My Metallica Premium started having an issue with Coffin Opto 1 (bottom). It thinks there's a ball there and the coffin post goes off constantly in an attempt to clear it.

During Switch Test, Opto 1 shows active. But, the LED on the associated opto board is on and turns off when I put a card between the optos in position 1. (Opto 2 and 3 also operate as expected.) Long story, but I had a new opto board and two optos, so just for grins, I switched them out. Same results.

So, my thinking is that the issue is upstream from the boards. Any suggestions for troubleshooting or likely culprits? Thanks.

Thanks Markmon. Finally got to spend some time with it last night. Confirmed continuity to the board, checked the connectors, etc. Found that one of the stand ups was triggering other switches in the same column. Turned out that a wire was touching a diode lead. I always feel like the pinball gods love torturing me. Anyway, so good to have the game working again.