A fuse blows the moment the game is switched on, or the fuses are good but a driver board power LED stays dark.

Shorted or open bridge rectifiers

Cause: A shorted bridge (or WPC-95 diode set) blows its fuse; an open one passes low or no voltage. Both are common. A bridge that tests good on the bench can still fail under load.

Checks

• Check which supply's LED is out and which fuse blows.
• Test the bridge out of circuit (see the bridge test procedure).

Fix

• Replace the bridge or diodes, and the matching filter capacitor if it is old.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• WPC power driver bridge rectifiers and +5 V regulator
• 12 V unregulated LED out on the driver board: open track to C8
• Check fuses F106/F101 with no lamps and no game start: shorted bridge diode
• Bridge rectifiers to use on WPC-S and earlier driver boards
• WPC-95: all the 20 V coils dead, fuse good
• Replacing a driver board bridge rectifier without tearing traces
• Testing a bridge rectifier out of circuit
• WPC-89/WPC-S driver board LEDs and test points

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)