Identifying AS-2518-51 and AS-2518-56 sound boards

Both carry a 6808 (or 6802) CPU, a 6820/6821 PIA and one sound ROM at U4 (a black ROM equivalent to a 2716 or 2532). The -56 adds a ribbon connector for a vocalizer board and jumpers that let it act as a -51 (page 65).

Systems

• Bally MPU AS-2518-35

Related tips

• Sound module -32 and -50 test points
• Bench-test a -51/-56 sound board with a test EPROM
• Sound Plus -56 and vocalizer test points
• No sound at all: start with the amplifier hiss
• Which -51/-56 sound ROMs respond to the board test button
• Odd 43 V coil faults on games with the early AS-2518-32 sound board
• Sound board chip 86L93 can be replaced by a 74LS93
• 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)