I'm looking at a guy's Stern Sting Ray with a goofy problem. He said after playing a number of games on it that the flippers would stop working but that everything else would operate correctly when the flippers were out. I have had the game for 3 weeks now and play it regularly. The flippers have never gone out so I can't duplicate his problem. However, twice, the knocker coil, when firing, locked on and took the game down. I turned the game off and on and it then played correctly.

I can put the knocker coil in test or set up playfield specials and fire the knocker coil a hundred times in a row with no issues. And yet, once every 100 games or so, it fires during play (when it's supposed to) and locks on.

It has an Altek MPU board in it. Everything else is original Stern. I cleared the ROMS on the MPU and resoldered several cold solder joints on the driver board. But the knocker still randomly locks on when firing. And the flippers have never failed.

Anybody heard of an INTERMITTANT transistor failure?? Any other ideas on what this could be that would occasionally lock on a coil? It is very confusing. Never saw a solenoid intermittently lock on before!