LED100 is out and switches stop working.

WPC-95 LED100 off (+12 V regulated)

Cause: Fuse F101 or F106. A blown F101 is often a failed CPU U20; also suspect regulator Q2 (LM7812). Path: J129 pins 4-7, F106, D11-D14, C11/C12, D1/D2, Q2, F101, then J101 pins 1-2.

Checks

• Check F101 and F106.
• Measure TP100 to TP107 for 12 V.

Fix

• Replace the fuse; then U20 or Q2 if it fails again.

Systems

• WPC-95

Related tips

• WPC-95: regulated 12 V fuse F101 blows
• Testing a WPC-95 rectifier diode
• Filter capacitors and GI triacs that fit WPC boards
• Supplies made on the WPC power driver board
• Trace the 12 V switch supply with the playfield disconnected
• 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

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