A sound board boots and plays its self-test sounds on the bench, but once fitted in the game it gives its boot flashes and no audio, even from its own test button. The original board works in the same game.

Spare sound board works on the bench but is silent in the game: no -5 V, bad 7905

Cause: The board was not making its own -5 V supply: diode CR7 was shorted and the 7905 negative regulator had failed. On the bench an external supply had been providing the voltage.

Checks

• Measure the -5 V on the sound board in the game.
• Check CR7 and the 7905 regulator.
• Make sure the board gets all of its supply inputs in the game, including the one that comes from the GI circuit.

Fix

• Replace the shorted diode CR7 and the 7905 regulator.

Systems

• Bally MPU AS-2518-35

Games

• Eight Ball Deluxe (LE)

Related tips

• MPU stops before the 7th flash until sound board power is unplugged: replace CR3
• Bench-test a -51/-56 sound board with a test EPROM
• Which -51/-56 sound ROMs respond to the board test button
• 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
• Sound Plus -56 and vocalizer test points

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