Bally: flipper relay won't fire in game: hairline trace break that still beeps
On a battery-damaged Bally MPU, the flipper relay wouldn't pull in during a game although the driver board worked in another machine and the traces metered fine. A hairline crack in the trace to pin 40 of a PIA still showed continuity on a meter, but a logic probe showed the line floating with the game running. A jumper wire over the cracked trace fixed it. If a signal is good on the bench but dies in the game, probe the live lines rather than trusting a continuity beep, and look closely at traces near old corrosion.
Systems
Related tips
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Source: Pinball Repair help group!! (Facebook group)