The entire switch matrix is dead.

No playfield switches work: check the regulated 12 V

Cause: Fuse F115 (F101 on WPC-95) blown, or no regulated +12 V: BR1 bridge or its solder joints, the LM7812 at Q2, or a bad trace to Q2.

Checks

• Game on in attract mode: TP3 (TP100 on WPC-95) should read +12 V DC; dips below 11 V cause erratic switches.
• If missing, check TP8 (TP102 on WPC-95) for +18 V, and the "+" (indented) lead of BR1 on WPC-S and earlier.
• If 18 V is present but not 12 V, suspect Q2 or its trace.

Fix

• Replace the fuse, BR1 (with jumper wires) or the LM7812 as found.

Systems

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

Related tips

• "Check Fuse F114/F115" (F106/F101 on WPC-95): step-by-step
• Row or column "ground short" errors
• One switch triggers others and flippers act oddly: drop target switch wired backwards
• Game accepts no coins and will not start
• Driver board LED1 off (+12 V regulated missing)
• WPC-95 LED100 off (+12 V regulated)
• Trace the 12 V switch supply with the playfield disconnected
• Switch matrix dead after a screwdriver slip under the playfield

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