The game makes no sound.

No sound at all: start with the amplifier hiss

Cause: Often something simple: a bad speaker or broken speaker lead, a worn volume pot, an unplugged sound board connector, a blown fuse, or a bad ground to the board (page 70).

Checks

• Turn the volume up and listen for the amplifier's background hiss; none means look at the pot, speaker, connector or fuse.
• Test the speaker and its leads.
• On a Squawk and Talk, work the two pots (sound and speech) back and forth with the game off, then set both near maximum.
• If there is no sound and a loud buzz, check the sound board ground wires and connectors.

Fix

• Replace the speaker, pot or fuse, or repair the connector or ground.

Systems

• Bally MPU AS-2518-35

Related tips

• Sound module -32 and -50 test points
• Identifying AS-2518-51 and AS-2518-56 sound boards
• AS-2518-51/-56 sound board jumpers
• Bench-test a -51/-56 sound board with a test EPROM
• Sound Plus -56 and vocalizer test points
• Which -51/-56 sound ROMs respond to the board test button
• Check the -51/-56 PIA, RAM and amplifier with the test EPROM running
• Background sound works in test but not in games: check DIPs 29-30, then reseat connectors

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)