One of these fuses blows when the game is switched on.

F3, F4 or F5 blows on the rectifier board

Cause: F3: bridge BR2 shorted. F4: bridge BR3 shorted (or the varistor). F5: a short somewhere in the GI wiring or a GI socket.

Checks

• Unplug J1 and J3 and power on: a fuse that still blows points to the rectifier board itself.

Fix

• Replace the shorted bridge with a 25 or 35 A wire-lead type.
• For F5, isolate the GI section as described in the GI fuse entry.

Line voltage (120 V AC) is present on the rectifier board and its J2 connector; unplug the game before touching it.

Systems

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

Related tips

• Rectifier board and playfield fuse ratings
• Which rectifier to suspect for each blown fuse
• Hot, discoloured fuse clips
• GI fuse F5 blows at power-up and coils lack voltage: rectifier board wires in wrong pins
• Main solenoid fuse F4 blows (hard short)
• Rectifier test point ranges with fuse and rectifier
• Finding a short that blows GI fuse F5
• Find a short that blows the 20 A GI fuse

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