The stock bridges are undersized

The original VJ248 bridges (200 V 8 A) are a known weak point; replace them with 25 or 35 A bridges. CR1-CR4, the display diodes, carry little current and seldom fail, but use 1N4007 or better if replacing them.

Systems

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

Related tips

• Getting at the bridges on -18/-49 boards
• Backbox GI out and fuse F6 blowing: burnt rectifier J3 plug and a shorted bridge
• Controlled lamps dim and TP1 reads about 2.8 V instead of 5.4 V: half the bridge open
• Solenoid board 5 V collapses under load: open 12 V bridge on the rectifier board
• Rectifier board test point voltages
• No +12 V at rectifier board TP3
• Solenoid driver TP5 under 13 V
• The three Bally rectifier boards

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