LED1 on the driver board is out; switches do not work.

Driver board LED1 off (+12 V regulated missing)

Cause: Fuse F115 has blown, often because CPU chip U20 has failed. The supply path is J101 pins 4-5 and 6-7, F114, BR1, C6/C7, diodes D1/D2, regulator Q2, F115, then J114 pins 1-2.

Checks

• Check F115, then F114.
• Measure TP3 to TP5 for 12 V.

Fix

• Replace F115; if it blows again, replace CPU U20 (ULN2803).

Systems

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

Related tips

• Driver board LED1 off: switch matrix 12 V missing (WPC-S and earlier)
• Driver board LED5 off: flasher 20 V missing (WPC-S and earlier)
• Driver board LED6 off: lamp matrix 18 V missing (WPC-S and earlier)
• Driver board LED5 off (+20 V flashers)
• Driver board LED7 off: unregulated 12 V missing (WPC-S and earlier)
• Driver board filter capacitors wear out
• 'Check F114 and F115' with switch 24 open: missing 12 V, bad bridge BR5
• Voltages made by the WPC power driver board

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