Fuse clips on the rectifier board are brown, loose or the fuse gets hot.

Hot, discoloured fuse clips

Cause: The clips have fatigued or corroded and now act as resistors; the high-current fuses suffer most.

Checks

• Look for discolouration and weak spring tension.

Fix

• Replace the clips; they cannot be restored.
• Use tin-plated beryllium copper clips, at least for high-current and high-voltage fuses, ideally for all.

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
• F3, F4 or F5 blows on the rectifier board
• 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
• What each rectifier on the board feeds
• Rectifier board test point voltages

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