At power-on the score displays show only zeros with Xs in them and the game will not start.

Displays show only 0s and Xs at power-on

Cause: The game sees the slam switch closed. The normally open slam switch above the coin door lock is often bent shut when coins are inserted.

Checks

• Check the slam switch is open.
• If it is fine, check the switch matrix, since the slam switch is part of it.

Fix

• Bend the slam switch open to restore its gap.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• A switch does not register in the switch test
• Knocker fires several times at power-on with a switch number shown
• One playfield switch does not register
• "Adjust Failure" at power-on
• Instant tilt and scrambled switch test: burnt resistor networks on the CPU
• How wiring faults show up in switch test
• All eight drop targets never register: check the drop target board plugs

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell