Working on a Bally GameShow and have multiple issues so sorry if this gets confusing.

With original MPU game will boot and play with a few issues:
1) On Left display only, Segments A and B (see pic) on all digits will not lite. Display and ribbon cable have been tested in another machine and work and spare MPU has been used and display works as it should so I'm assuming it's an issue on the original MPU. Where to go from here?

2)After game warms up (a minute or few) ball trough kickover coil will stutter and tend to lock on. Corresponding switch works proper in test. Transistor and pre driver replaced and same issue. Using a spare MPU it works as it should. What should I be looking at on original MPU?

3) Ball trough up-kick to shooter lane coil doesn't work in game or test mode. Transistor replaced and pre driver. Corresponding switches register in test. Grounding transistor fires coil (original mpu) and using spare MPU it works as it should. Where to test next?

4) Solenoid 16 - Backbox teeth and title Flashers do not work. 4 flashers total in chain. With meter probe on ground strap and either of the socket lugs I'm getting like 42Volts DC on all 4. Bulbs are not blown. Grounded the center lug on one socket and all 4 instantly blew. These do not work with spare mpu installed either???

WITH SPARE MPU (think it's an 11B but have to look again) installed:
- issues 1 through 3 above go away - issue 4 above consistent
- NEW PROBLEM - ALL "Special" Solenoids do not work. All worked with original mpu. 3 pop bumpers and 2 slings. All corresponding switches work proper in test and if I ground all transistors all coils fire. Transistors are all in spec. All located in same area on board (see red circle on pic). Replace a chip?

Any help appreciated. thanks

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Still need help but some progress. Concerning issues 2 and 3 above, I replaced pre drivers (thought i had before but guess not) Q29,Q21 on original mpu. Trough kick over does not lock on anymore but it and the trough upkick still do not work. Both work if I ground the transistor tabs Q33,Q25. Corresponding switches work. Should I try replacing SR7 or SR6? ...or just go straight for U20?

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uggghhh...trough kick over is locking on again

ALSO - I seem to have continuity to ground from the middle leg on Q21 and Q29...all other pre-drivers do not???

Update - All original issues on original mpu are solved!

1 - Changed SRC2 and U41
2+3 - Changed Q21,Q29 and U20
4 - R10 on interconnect board was bad

Also in regards to spare mpu and special solenoids not working - was told to use an 11A board in 11B or later games you need to add diodes -See pic attached - Have not done mod to confirm

After changing U41 I have a new issue - see new thread if interested

https://pinside.com/pinball/forum/topic/system-11c-plays-but-sound-garbled-no-background-d-11581

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