Setting up Leon's System 11 CPU test EPROM

Steps

• Program the System 11 test file into a 27512 EPROM.
• Take the CPU board out and power it from a 5 V supply: +5 V to 1J17 pin 4, ground to 1J17 pin 3.
• Jumper the right side of zener ZR1 (just left of the batteries) to +5 V.
• Optional: wire an LED in series with a 150 ohm resistor between +5 V and U15 pin 15 (address line 6) as a "running" indicator.
• Remove the game ROM from U27 and fit the test EPROM there.
• Power up: every PIA output should toggle between 0 and +5 V about once a second; the indicator LED should blink. If no PIA toggles, suspect the CPU chip or its address/data/select lines.

Systems

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

Related tips

• Which System 11 CPU boards fit which games
• 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
• System 11A-11C CPU LEDs: normal state
• Early System 11 CPU in a later game gives meaningless LED codes
• System 11A jumpers W16 and W17 depend on the CPU chip brand

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