Running the CPU board on the bench

Steps

• Unplug every CPU connector except 1J17 (power); this limits damage to other boards while you test.
• Better still, take the board out and power it from a PC or arcade switching supply. On PC supplies red is usually +5 V, yellow +12 V and black ground; confirm with a meter.
• 1J17 pinout: pins 1-3 ground, pins 4-6 +5 V, pin 7 key, pin 8 -12 V (audio only, not needed), pin 9 +12 V.
• Connect with clip leads.

Systems

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

Related tips

• Free-running the CPU to check address and select lines
• Which System 11 CPU boards fit which games
• Checking the CPU clock signal
• CPU RAM at U25
• CPU board test switches SW1 and SW2
• What each 6821 PIA on the CPU board controls
• Checking PIA outputs with the test EPROM running
• Which System 11 CPU boards swap between generations

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