No sound at all.

Sound board completely dead

Cause: A blown sound board fuse, a failed bridge rectifier, or a shorted 7805. A shorted 7805 puts 12-18 V on the 5 V line and can kill the EPROM, CPU, PIA and RAM.

Checks

• Check the sound board fuses.
• At the test points measure +12 V, -12 V and +5 V; +5 V must be between 4.75 and 5.25 V.

Fix

• Replace the fuse, bridge or regulator; if the 5 V line was overvolted, check the logic chips too.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• The sound board is its own computer
• Sounds don't match the game or die mid-game: sagging 7805 on the sound board
• Which sound board each game uses
• Sound board jumpers for 2K sound-only games
• Powering a sound board for testing
• How System 3-6 games trigger sounds
• Type 1 and type 2 sound boards and their switches
• Setting up a sound board for speech

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)