The rising background sound plays in sound test but not during a game; the other sound effects still work.

Background sound works in test but not in games: check DIPs 29-30, then reseat connectors

Cause: On this game the background sound is enabled by MPU DIP switches 29 and 30. In this case they were already on, and the fault was a poor connection: reseating the power supply, MPU and driver connectors cured it.

Checks

• Confirm MPU DIP switches 29 and 30 are on, and power cycle after any change.
• Reseat (and if needed repin) the connectors between the power supply, MPU, sound board and driver board.

Fix

• Set the DIP switches correctly, then reseat or repin the board connectors.

Systems

• Bally MPU AS-2518-35

Games

• Silverball Mania

Related tips

• No background music, only target sounds: set feature adjustment 18 to 03
• No sound and no 12 V at the sound board test point: burnt-open R22
• Background sounds clear but the speech has heavy static: recap and reflow the sound board
• 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

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