Spare MPU and driver chips with their locations

Solenoid driver pre-driver array: CA3081 (NTE916). MPU: 6820 or 6821 PIAs at U10/U11, 6800 or 68B00 CPU at U9, 555 at U12, 4011 at U19, 4049B at U14/U18, 9602 at U16, 14502B (4502) at U20, 5101 RAM at U8 and a 7437 or 74S37 at U15. Display decoder: MC14543 (4543). Lamp driver decoder: CD4514.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Keep spare 6800, 6821 and 5101 chips
• Reseat the MPU chips before anything else
• Strip the MPU to three chips to get the first flicker
• Power and ground pins of the main MPU chips
• Double-check bench leads: a +12 V to +5 V short kills the MPU chips
• Testing an MPU in the game with only J4 connected
• MPU board test points
• MPU board test point voltages

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