Replace filter cap C23 on every game
C23 is the big blue filter cap (about 12,000 uF 20 V) that smooths the 12 V before the +5 V regulator. Electrolytics dry out after about ten years, letting ripple into the 5 V and causing random resets. Every original is overdue.
Systems
Related tips
- Replacing filter cap C23
- MPU locks with LED on because of C23 or Q20 on the solenoid driver board
- Solenoid driver TP5 under 13 V
- Solenoid driver TP1 below 5 V with TP5 normal
- Only about 1.6 V at solenoid driver TP1
- Route of the +12 V supply to the MPU and 5 V regulator
- Logic 5 V reads over 5.25 V on Bally/Stern: the R49 boost resistor
- Adding a ground jumper at C23
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part One, Clay Harrell (pinrepair.com)