Fitting a remote AA battery pack

Steps

• Use a holder for three AA cells (a four-cell holder with one slot bridged works).
• Put a blocking diode (1N4001 or 1N4004, or a 1N5817 with less voltage drop) in the positive lead so the board cannot charge the cells.
• Connect the diode band to the board's "+" battery pad and the other end to the pack's positive lead.

Systems

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

Related tips

• Fit a remote AA battery pack with a blocking diode
• Cleaning minor battery corrosion on the CPU board before fitting NVRAM
• Battery power not reaching the RAM: diode D2
• New CPU batteries go flat quickly
• Repairing battery corrosion on the MPU
• Cut the original MPU battery off right away
• Bally-35 MPU: remove the on-board rechargeable battery before it leaks
• Reset section parts typically ruined by battery corrosion

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