Now and then the LEDs report a U10 PIA failure at power-on, yet the game plays normally after a good boot.

Occasional U10 PIA error at power-on, but the game plays

Cause: +5 V below about 4.9 V DC, often from a worn +5/+12 V filter capacitor.

Checks

• Measure +5 V at the CPU board.

Fix

• Replace the power supply filter capacitor (C10) and other low +5 V causes. Left unfixed this can damage the special solenoid circuit.

Systems

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

Games

• F-14 Tomcat

Related tips

• Spinner works in switch test but scores nothing in play: factory reset
• MPU won't boot even though a test ROM passes every PIA and RAM: bad game ROMs
• Game will not boot consistently: power-on reset (POR) circuit
• "Adjust Failure" at power-on
• "IRQ Failure" at power-on
• Won't boot even with a new CPU board and new chips: the new ROMs were bad
• Won't boot after restoration, new EPROMs fitted: try the original ROMs
• Game resets when the flippers are used: recap supply and renew MPU power connector

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