I have an NBAFB. For a while the ball eject has fired softly while in gameplay. Not hard enough to get a ball to the lane so it wasn't causing gameplay issues. Every once in a while a ball would fire into the lane. I switched the trough opto boards with another WPC game I had which is now gone. When I did, the same issues continued so it's not the trough boards themselves.
Today I turned the game on and in attract it's just continually firing the balls out. Looking at the Opto PCB it looks like some fixes were done there. LM339 chips looks like they were replaced at some point. I reflowed solder on the board but no change. I've found reference to the board and chips being bad when an opto isn't registering right but could it contribute to random ball firings like this too? Everything is fine in switch test.

In switch test everything has checked out.
Trough eject (jam) shows closed and if I pass something in front it opens. All 4 ball optos register correctly. I can leave test up and nothing ever flickers. Hit every switch and no phantom closures. I’ve smacked the cabinet and playfield to see if something happens and nothing there.
Right now it’s not launching all the balls. It’s back to where it’s been. I played a couple games and can feel the ball eject fire and hear the balls move. In multiball the correct number come out. It’s just so random. I could hold a ball at the flipper and it does it. Solenoid fires quickly and balls move.
It’s a 7 switch board. Just connects to the trough.

So tonight I found in switch test with the button pulled out to enable high voltage and hitting both flippers together that the optos would register. With all balls out so that all 7 optos in the column were closed they would all together flash open. Every 5-10 times hitting both flippers together would do it. The eight switch in the column is a standard rollover and it never reacted. Only the optos. All are on the same opto board.
After starting a game hitting the flippers separately will cause all playfield lights to react like they do when entering a ramp. Even with the ball out of the game. In switch test hitting both flippers causes the above optos flash but nothing individually.
Also the game never goes into ball search. I can grab a ball with the glass off and every few seconds a call out will happen like the game thinks things are happening.
Strange things.