Find a short that blows the 20 A GI fuse

Steps

• The only GI part on the rectifier board is the 20 A fuse (page 80), so look outside the board unless the fuse still blows with J1 and J3 unplugged.
• Disconnect the GI feeds to the backbox, cabinet and playfield in turn to find the section at fault.
• Within that section, there are two GI circuits (red/white and green/orange); disconnect individual strings until the fuse holds.
• Look for shorted wires or sockets, swapped wires, or a #44 bulb with a stray filament lead touching the socket.

Systems

• Bally MPU AS-2518-35

Related tips

• Finding a short that blows GI fuse F5
• No general illumination after a new rectifier board, fuses good: check the bulbs
• No feature lamp voltage at TP1 (-18 board)
• How Bally controlled lamps are powered and switched
• None of the controlled lamps light
• Dim controlled lamps and a buzzing expander relay
• F3, F4 or F5 blows on the rectifier board
• Main solenoid fuse F4 blows (hard short)

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