I got this F-14 Tomcat that came with a blown fuse (the 4A slow blow in the backbox that appears to be responsible for high power). It blew again after replacing it, of course. The first thing I did was rebuild all 4 flippers, I noticed on the upper right flipper the big yellow cylinder thing (capacitor?) was disconnected. I reconnected that, and now the fuse no longer blows.

However, now there is very strange behavior. The game will act fine for a while, but then at some point the flippers die, and plunging in to the lock ends the ball. Sometimes power cycling fixes it, some times manually removing balls from the lock fixes it, but some times it gets stuck in this state for a while. The only clue I have is that, as I said, when the flippers are dead, delivering the ball in to a lock goes to End of Ball Bonus. Very mysterious.

What sort of things should I be checking? Could this be the fault of a bad transistor doing all sorts of wonky things? Bad diodes somewhere? Where should I start?

Hmm interesting... which board is this on? If I can borrow a board from someone's game, which one should I swap out?

I swapped the MPU with a working one and the problem persists. Must be in the playfield, or bad ROM chip.
If it's a playfield issue, should I look for bad diodes? Capacitors? General badness?

I found out the outhole kicker is locked on (started smelling...) and sometimes the flasher #1 goes very very bright. Investigating D1 and D9 on diode board now... Could it be possible the entire Solenoid 14 relay is messing up? That switches between the A solenoids and the C solenoids?