Sounds like a few random issues, are there any exposed wires leading into the connector on J120 / 121? as well as J127/J130. If so some of those wires might be hanging on by a thread into those connectors. Same goes for the 12V digital for the the opto stuff at J114 I think. Continuity is one thing, resistance is probably your problem.

I think it was suggested to re-seat all your connectors (game off) first. But look closely for oxidized female connector parts and lousy crimp jobs.

WCS is a 5 ball game

I'd remove your reset bypass, It's good to know about a reset because it's a clue to something. If this game is new to you and the original power board was most likely good it sounds like to me. Send your MPU, SND, Fliptronics II board along with the Display board to Clives Cauldron for testing. While they are there deal with the clean up of the rest of the machine.

That's fantastic news! I won't ask what you did with that wire but glad it's making sense to you.

You have an erroneous ball drain.. Oh boy.. so your saying it get's worse?! for my drain the ball has to end up in the final draw trough or it did happen once from a goal.

I'll start putting more effort into that, right now I have a broken Centaur so NFG takes priority to bring my workingish game percentage up!

That's great, I was thinking of re-seating all the 12V opto cables to and from everything since it revolves around optos, it's such a rare occurrence. I'm curious if your referring to LED5 as being a transmitter?