After a blown tantalum capacitor (C10, on the unregulated 12 V input) was replaced, the board only gives a low hum with very faint but correct tones; the volume trimmer changes the level.

Cheap Squeak sound board gives only faint tones and hum: failed DAC

Cause: The digital-to-analogue converter chip had failed (probably in the same event that blew C10).

Checks

• Replace the capacitors in the audio path, the audio amps and the 5 V regulator first if suspect.
• Swap in known-good socketed chips and ROMs.
• With a scope, follow the signal to see where it disappears.

Fix

• Replace the DAC.

Systems

• Bally MPU AS-2518-35
• Bally 6803

Related tips

• Sound died: Cheap Squeak clock test point stuck high, bad crystal
• Some sounds only tick or click: the 4526 counter on the sound board

Source: Pinball Repair help group!! (Facebook group)