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Check signal line PB3, pin 13 of U38 PIA with a logic probe or oscilloscope. I'd certainly be suspicious of the PIA. I can tell you this never would have been transistor related in the first place, as the transistor is basically a "dumb switch", and something upstream has been turning it on and off.
Quoted from 1iblind:Got the logic probe and tested pin 13. It was reading high, low, and pulsing. I left the game on a few minutes and went back to testing. This time the pins around 13 were reading low but 13 was reading high. So I replaced U38 but still had the solenoid clicking on and off and eventually staying on. Logic probe read high, low, and pulse. Waited a few minutes with no change in reading. The relay works fine in test when switching from A to C but still clicks about 8 times on power up.
Wow. That sounds strange. If the A/C switching works consistently in test mode, then that pretty much confirms everything from the PIA to the coil is ok. Higher level logic problem, I think. Maybe game ROMs or RAM.
You can buy or borrow a RAM tester, or build one from a kit https://pinside.com/pinball/forum/topic/williams-system-11-u25-part-no-needed
Or, just replace it with NVRAM and never worry about changing batteries again https://www.pinballlife.com/anypin-dmd-nvram-battery-eliminator.html
Quoted from wayout440:You can buy or borrow a RAM tester, or build one from a kit https://pinside.com/pinball/forum/topic/williams-system-11-u25-part-no-needed
Or, just replace it with NVRAM and never worry about changing batteries again https://www.pinballlife.com/anypin-dmd-nvram-battery-eliminator.html
Any battery alkaline corrosion on this mainboard?
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Berea, OH