The 5 V supply from the solenoid driver board measures only about 4 V. An original MPU may still boot, but a replacement (Alltek) MPU does not, and the sound board may stop working, even with a new regulator, new filter capacitor, reflowed headers and the ground mods done.
Bally solenoid driver 5 V reads only about 4 V: swap the drop-in regulator
Cause: The aftermarket drop-in replacement for the LM323 5 V regulator was not delivering a full 5 V on this board.
Checks
- Measure the 5 V test point on the solenoid driver board with the boards connected.
- If the fitted regulator is a switching drop-in type with a trim pot, see whether it can be adjusted up to 5 V; in some cases it cannot.
Fix
- Replace the aftermarket regulator with an original-style LM323 and recheck the 5 V line.
Systems
Related tips
- No +5 V on a System 3-6 power supply
- MPU won't boot and driver board test points read low: replace the solenoid driver board
- Replacing C23 on a Bally/Stern solenoid driver: follow the board's + marking
- MPU locks with LED on because of C23 or Q20 on the solenoid driver board
- Route of the +12 V supply to the MPU and 5 V regulator
- No +5V on any board and no MPU LED: bad return pin in the solenoid driver board J3 plug
- Only about 1.6 V at solenoid driver TP1
- Solenoid driver TP1 below 5 V with TP5 normal
Source: Pinball Repair help group!! (Facebook group)