A 24 VAC center-tapped transformer for running game ROMs on the bench

The test EPROM needs only +5 and +12 V, but to run the real game ROMs on the bench the board also wants 2x12 VAC from a 24 V center-tapped transformer: center tap to ground (J1 pins 7-9) and the two 12 V legs to J1 pins 3 and 4.

Systems

• Bally 6803

Related tips

• Final bench test with the real game ROMs
• Which games use one or two game ROMs
• Bench-test a CPU board with the 6803 test EPROM
• CPU board landmarks: battery, LED, relay and ROMs
• Test EPROM fitted but the LED does not blink
• Interrupt circuit failure from the 2x12 VAC signal
• Electronic spares for 6803 board repair
• Cybernaut can have a -35, 6802 or 6803 boardset

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)