Checking the pre-Xenon supply with the game unplugged from it

Steps

• Unplug J1 and J3 from the rectifier board, leaving only J2 (line power) connected.
• Take ground from the R1 or R2 lead nearest the fuses (on an AS2518-54, the right-hand lead of R1).
• Power on and read TP1 to TP5 against the expected ranges.
• A low or missing reading points to that output's fuse or bridge.

Line voltage (120 V AC) is present on the rectifier board and its J2 connector; unplug the game before touching it. The score display supply runs at 170-230 V DC; keep hands off the rectifier and driver boards with power on.

Systems

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

Related tips

• Where the 43 V solenoid supply leaves the rectifier board
• How the pre-Xenon power supply works
• Solenoid driver TP5 under 13 V
• Solenoid fuse blows even with the outputs unplugged: fault on the rectifier board
• Rectifier board test point voltages
• No +12 V at rectifier board TP3
• The stock bridges are undersized
• What each rectifier on the board feeds

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