Pressing Begin Test on the coin door does nothing.

Game will not enter test mode

Cause: The test switch, its ground wire, the coin door connector, or U15 on the CPU board.

Checks

• Check the test switch and that its ground wire is attached.
• Check CPU connector J205 for poor contact.
• Check U15.

Fix

• Repair the switch or wiring, clean or repin J205, or replace U15.

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 accepts no coins and will not start
• 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)