Power and ground pins of the main MPU chips

+5 V should be 4.8 to 5.2 V measured at the chip itself. U6, U2 (ROM): +5 V pin 24, ground pin 12. U9 (6800 CPU): +5 V pin 8, ground pins 1 and 21. PIAs U10 and U11: +5 V pin 20, ground pin 1. U8 (5101): +5 V pin 22, ground pin 8. U7 (6810): +5 V pin 24, ground pin 1.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• Add a ground jumper on every -17/-35 MPU
• Using a PC power supply as an MPU bench supply: which wires
• Reseat the MPU chips before anything else
• Tell a -35/-133 MPU from a -17 by counting J5 pins
• MPU LED never lights at all
• Strip the MPU to three chips to get the first flicker
• Double-check bench leads: a +12 V to +5 V short kills the MPU chips
• MPU stops before the 7th LED flash (no 43 V)

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)