Using the Williams System 11 test fixture EPROM

Steps

• Program the Williams test image into a 27256 EPROM.
• Fit it at U27 with the notch to the right; the game EPROM at U26 can stay.
• Power on: the game boots to an attract mode that says the test fixture EPROM is fitted.
• Enter diagnostics as usual (centre button down, Advance, centre button up, Advance through tests). The tests go only slightly deeper than the standard ones.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Which System 11 CPU boards fit which games
• Checking PIA outputs with the test EPROM running
• Testing U25 RAM with Leon's EPROM
• Which System 11 CPU boards swap between generations
• How to tell a System 11C CPU from an 11B
• System 11 CPU board part numbers and spotting features
• Game EPROMs with missing window labels may be erased
• System 11A-11C CPU LEDs: normal state

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)