The game will not boot and LED101 is out.

WPC-95 LED101 off (+5 V, game will not boot)

Cause: Fuse F105, diodes D7-D10 or capacitor C9; rarely regulator Q1. Path: J129 pins 1-2, F105, D7-D10, C9, Q1, then J101 pins 3-4 and pin 4 of J138 to J141.

Checks

• Check F105.
• Measure TP101.

Fix

• Replace the failed fuse, diodes or capacitor.

Systems

• WPC-95

Related tips

• Testing a WPC-95 rectifier diode
• WPC-95 driver board LEDs and test points
• Filter capacitors and GI triacs that fit WPC boards
• Supplies made on the WPC power driver board
• Adding backup jumpers to a WPC-95 driver board
• WPC-95 filter capacitors are smaller (10,000 mfd)
• WPC-95 uses discrete P600D diodes instead of bridges
• WPC-95 rectifier diodes, filter caps and fuses by supply

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