A loud, steady hum from the speakers; its tone shifts with display or lamp activity, but the volume knob makes no difference.
Loud constant hum that the volume control does not change
Cause: The CPU board is not grounded well to the backbox because mounting screws are loose or missing; the sound section is on that board. The amplifier itself is fine, since volume has no effect.
Checks
- Check all eight CPU board mounting screws are present and tight.
- Check the sound board mounting screws too.
Fix
- Fit and tighten every mounting screw.
Systems
Related tips
- Constant hum instead of sound: shorted capacitor C26 on the sound board
- Power-on sound tones and what they mean
- No sound after board work: 1J15 and 1J16 swapped (they aren't keyed)
- Volume suddenly goes to full blast and the volume pot does nothing: shorted pot wiring
- Game-over music missing: reflow the sound board header pins
- How System 11 makes sound
- CPU sound diagnostic switch SW1 results
- No sound from SW1 although sounds play in diagnostics
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)