The display shows "IRQ Failure" when the game is switched on.

"IRQ Failure" at power-on

Cause: Usually the +5 V supply is too low.

Checks

• Measure +5 V: it should be 4.9 to 5.1 V DC.

Fix

• Fix the low +5 V (C8, C10, BR1 on the power supply).

Systems

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

Related tips

• "Adjust Failure" at power-on
• Displays flash bright and speakers noisy, game does nothing
• Occasional U10 PIA error at power-on, but the game plays
• Four beeps at power-up, GI only and no display: game has no batteries
• Won't boot after restoration, new EPROMs fitted: try the original ROMs
• Resets continue after diode repair: power and connector checks
• Game resets when the flippers are used: recap supply and renew MPU power connector
• Game will not boot consistently: power-on reset (POR) circuit

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)