Background sounds and effects are clean, but the spoken call-outs are buried in heavy static. Recapping the speech board alone did not cure it.

Background sounds clear but the speech has heavy static: recap and reflow the sound board

Cause: Failing capacitors on the main sound board (the large 4700 uF filter capacitor was the poster's main suspect), along with tired solder joints and diodes on the sound and speech boards.

Checks

• Clean the volume pot by spraying it with contact cleaner and working it back and forth; that has cured similar crackle for others.
• Look at the sound board's filter and electrolytic capacitors and solder joints.

Fix

• Replace all the electrolytic capacitors on the sound board as well as the speech board, reflow the joints, replace suspect diodes, and clean the chip legs.

Systems

• Bally MPU AS-2518-35

Games

• Xenon

Related tips

• Sound Plus -56 and vocalizer test points
• Background sound works in test but not in games: check DIPs 29-30, then reseat connectors
• 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
• No sound at all: start with the amplifier hiss
• Which -51/-56 sound ROMs respond to the board test button

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