I have a Williams System 11 Road Kings that started acting up. During game play, the outhole ejector would start kicking the ball in the trough out into the shooter lane once the game was on for several minutes (it would play fine when cold). It wouldn't fire the ejector fast though, maybe about once every 30 seconds, it would kick a ball out into the lane. After kicking the ball out several times durning a game, it would blow the F5 on the power board. I was thinking that maybe the transistor was shorting when getting warmed up. As a note, this game came with a Rottendog power board (all voltages checked and are good). All other boards are original.

I replace the corresponding outhole ejector transistor, Q25, with a TIP 102 as well as the corresponding predriver transistor (Q21, I believe - going from memory) with a 2N4401. While I was at it, I also replaced that coil with a new 23-850 SG I had on the shelf.

I turned the game on, got a couple minutes into it a game, then the ejector popped the ball into the lane and stayed locked on. I shut the game down instantly to prevent coil damage (it was fine, hardly even got warm). I replaced the the same two transistors again and just to verify it wasn't a defective transistor, but the same results; plays for a few minutes then locks the coil on.

To recap:
Former State = Plays fine for a while then ejector would repeatedly eject balls into the lane until F5 blew.
Current State (with new transistors and coil) = Plays fine for a while then ejector locks on and blows Q23 and predriver Q21.

What else should I be looking at if it isn't the coil or transistors? Thanks!

I'll check the outhole microswitch when I get home, thanks.

I checked the microswitch on the outhole and it is functioning properly and the wires are soldering on firmly with no frays. I replaced the diode on it for good measure, no difference.

Sorry for the delay, I was waiting for parts to arrive. I ended up replacing the 7408 at U20 and everything seems to be working now. Thanks for the help.