With the test EPROM fitted the LED never gives its first long flash, or stays lit.

Test EPROM: no long flash, or LED stuck on

Cause: The CPU core is not running: reset, clock, the 6502 itself, a broken trace, a chip jamming the data or address bus, or the U3 select and address buffer logic.

Checks

• 6502 pin 40 (reset) should be at 5 V.
• Clock should be present at 6502 pin 37.
• Z3 must be a plain 7404, not LS, HCT or S.
• Check traces, especially after battery damage or earlier repairs.
• Pull the 5101, U2 and the three RIOTs; if the long flash then appears, refit them one at a time to find the bad one.
• Check select logic and address buffers Z7, Z8, Z9, Z10 and Z12.

Fix

• Replace the faulty part or repair the trace.

Systems

• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B

Related tips

• Test EPROM 2: game PROM socket test fails
• Test EPROM stalls at the switch matrix RIOT (U4)
• Test EPROM stalls at the display or lamp/solenoid RIOT
• Replacing U2 and U3 with one 2764 EPROM
• Ways to fit EPROMs at U2/U3
• Which System 80 test EPROM image to use
• Single-ROM CPU board won't boot in an early two-PROM game
• Bench setup for the System 80 test EPROM

Source: Gottlieb System 80 Test EPROM V3.2 (February 2015), Pinitech