So, I just did a full restoration/playfield swap on a Sega X-Files, and it plays gorgeously, but there is one issue which is nagging at me. Whenever I put the playfield back into the game, my first tasks are to run the coil and switch tests. There are 2 optos on X-Files, one in front of the other; the front one activates a playfield magnet, and the back one registers a hit on the file cabinet toy.
When I was testing the switches, only the back opto was registering. This should mean that it will keep track of hits on the cabinet, but no magnet action. Furthermore, when I interrupt the path of the beam, the receiver LED lights up and the sender LED goes out, just like it's supposed to, and when playing the game, the magnet does in fact activate.

Is this just one of those situation where you go "huh, that's weird, oh well" and get on with it? It feels like having an itch I can't scratch.

Yeah, the back opto when I interrupt the beam indicates the correct switch position, "cabinet", not magnet. Really weird.

Looks like I figured this out...small transistor on opto board had a just-barely broken wire leg at the solder joint. Presumably it is part of what sends the signal to the CPU; currently waiting on GPE to re-open so that I can get a 12 cent replacement part