Game boots but ignores coins and the start button.

Game accepts no coins and will not start

Cause: The switch matrix is dead: blown F115, a fault at the start switch wiring, dirty CPU switch connectors, or failed U20 or U18 on the CPU board.

Checks

• Check fuse F115 on the driver board.
• Check switch 13 (start): both wires (green-brown and white-orange) need to be attached.
• Inspect CPU connectors J206 to J209.
• U20 pin 1 should be high and pin 18 low; U18 pins 2 and 5 low. Check D5.

Fix

• Replace whatever failed: fuse, wiring, connector or chip.

Systems

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

Related tips

• Pressing the coin-door buttons does not enter test mode
• A dedicated (direct) switch does not work
• Game will not enter test mode
• Switch rows 1-3 show shorted to ground: opto board missing its column strobe
• A whole switch column stops working: replace the ULN2803 column driver at U20
• Phantom switch closure that survives a new CPU board: bad 4N25 on the driver board
• WPC-89 CPU: one switch column still dead after a short: trace U14 to U20 to J206
• Lifting targets give a motor up error: broken wires and a bad up switch

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