No game sounds; turning the volume makes a scratch in the speakers and the CPU sound test button plays only faintly.

Pinbot sound suddenly dies but the amp hisses

Cause: The -12 V DC used for sound is missing because the bridge rectifier making it from 12 V AC failed.

Checks

• Measure for -12 V DC at the sound circuitry.

Fix

• Replace the failed bridge rectifier.

Measurements are taken with the game on; keep clear of the line-voltage wiring and the high-voltage display supply.

Systems

• Williams System 11A

Games

• Pinbot

Related tips

• Loud hum from the speakers in attract mode
• Whole game flickers off and on, then dies: burnt ground pin at the power supply board
• Speech drops out after 20-30 minutes, back after a reboot: speech chip on the MPU
• Which System 11 sound board each game uses
• D-11297, D-11298 and D-12338 sound boards
• Checking ground and +5 V on the CPU board
• Displays blank but the game plays
• Occasional U10 PIA error at power-on, but the game plays

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