U1 checks out but the LED still does not blink with the test EPROM fitted.

Test EPROM socket signals at U3

Cause: A bad U6 address latch, U5 data latch, the EPROM itself, or the chip-select from U9/U10.

Checks

• U3 pins 1-13, 15-19 and 22 should read 2 to 4 V; pins 14 and 20 about 0 V; pins 21, 23 and 24 about 0.5 V.
• A missing address line (pins 1-8) means U6 or the EPROM; a missing data line means U5; a missing select at pin 22 means U9 or U10.

Fix

• Replace the faulty latch, gate or EPROM.

Systems

• Bally 6803

Related tips

• Test EPROM fitted but the LED does not blink
• Test EPROM memory test does not pass
• Unplug all but J1 when using the test EPROM in the game
• Bench-test a CPU board with the 6803 test EPROM
• CPU board landmarks: battery, LED, relay and ROMs
• CPU jumpers JW1-JW6 for game EPROM size
• Check the 6803 clock at U1 pins 2 and 3
• Interrupt circuit failure from the 2x12 VAC signal

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