The test stops before the burst of two flashes.

Test EPROM stalls at the switch matrix RIOT (U4)

Cause: RIOT U4 has failed, often from a short between a coil circuit and the switch matrix (for example adjusting an EOS or pop bumper switch with the game on), or its clock or select logic is bad.

Checks

• Check for a clock on pin 39 of the RIOTs; if missing, check clock buffer Z3 and the nearby traces, often eaten by battery corrosion.
• Suspect U4 itself, and check switch matrix buffers Z11 to Z15, which often die with it.
• Check select chips Z7 and Z8.

Fix

• Replace U4 and any damaged buffers. Never adjust playfield switches with the power on.

Systems

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

Related tips

• Test EPROM 2: game PROM socket test fails
• Test EPROM stalls before the RAM pass flash
• Testing the DIP switch inputs with the test EPROM
• System 80 test EPROM LED flash codes
• Test EPROM: no long flash, or LED stuck on
• Replacing U2 and U3 with one 2764 EPROM
• System 80 DIP switches 25 to 32
• Ways to fit EPROMs at U2/U3

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