hello to everyone , I have this WPC95 MPU that as soon as the power goes through the machine, energizes the right lower flipper.
The coil remains stuck on until power is removed either by opening the coindoor or shutting down the pin. The solenoid goes stuck on even in test menu, it is not necessary to start a game.

I am pretty sure the problem is on the MPU and not elswhere (ex. a shorting transistor on PDB) because the problem moves through the machines swapping MPU boards..

I have consulted the schematics and think that the problem is in the yellow area(attached image), maybe some failed component let the MPU "think" that the related LR Flipper switch is pressed and activates the coil? Is it possible ? I'm not really sure how to narrow down to the culprit component, I have tested resistors with dmm and they are ok, note that all the lm339 and other ic on the board had been replaced and socketed except the U25 and U7 on this circuit!

Any advice on what to do now? I'd rather don't shotgun replace parts...
Please feel free to correct me if you think i'm on the wrong track!

thanks in advance for your precious help!

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thank you for your reply Chris, this seems odd to me too! I'll try to do more tests about it and let you all know! which fuse you suggest to remove??

Here I am! Finally I had time to do some tests! Here is a Pic of the switch matrix from switch edge test on the pinball (it's a MM) as you see the UR and LR Flipper switch both result open (they are optos). I tried to disconnect the right flipper opto board and j212 on the mpu but the situation doesn't change, the right flipper still stays stuck on (and the matrix remains as in the photo)

If I remove fuse 115, as suggested, the right flipper stays down but I think it is normal since it doesn't have the 50v through it...

what do you think I should do now? which component could cause this situation? should I replace U25 on the MPU?

thank you in advance!!

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Thanks for the reply, I have a logic probe but never used it before where should i hook the probe to take the necessary voltage while machine is powered on ?

Tested with logic probe, here the results:

IC U25-1 and U25-14 are both low
Resistors r111 and r113 are both low

IC U25-9 and U25-7 are both high
Resistors r99 and r103 are both high

What do you think? We have a culprit?

Update! replaced U25 and the problem is solved! I have another issue with crackling speakers on this pin, but I'll do a separate post later! Meanwhile, thank you for your help!!