Hi! I picked up a non-working Williams Flash a couple weeks ago. I've got it partially working now, but am having some switch issues.
This machine has the Rottendog MPU327 in it. Supposedly it had been "serviced" but I'm not too sure on the backstory of it. I know next to nothing when it comes to the boards.

Anyway, here are the switch issues I'm having --
(Switch matrix chart: https://www.pinitech.com/switch_database.php?name=Williams_Flash)

#1 Row 1 switches randomly fire when playing the game, and in switch test mode. During the game, they will randomly fire for a few seconds at the start of each ball (you get some points, and hear the "tilt" sound at least once). During the turn, it may happen again, or it might not - rather you are playing or not the switches will randomly fire in that row... again you hear it ring up points and/or tilt. I did try disconnecting the wires that go to the switches from the board (I believe it's 2J2 and 2J3?) and the switches still fire in test mode.

#2 Row 3 switches sometimes work, but normally don't. Most times, I cannot even get the start (credit button - Switch 3) to work (machine is on free play). All of the switches themselves look good, wires/diodes attached, so not sure what is wrong here.

#3 The coil for the eject hole (switch 27) will randomly fire on a few times when the game is first turned on, and occasionally during game play. I've noticed hitting the top drop target on the left 5 bank (switch 32) will fire the eject hole coil (switch 27) during game play every time (That is, if I can get it to start a game!).

Any ideas on what to check next? I'm assuming it's moreso board issues.