CPU plug A1J6 (coin door) pins

Pin 1 ground (green/yellow); 2 slam (orange/black/black); 3 return 0 (black/blue/blue); 4 strobe 1 (black/red/red); 5 strobe 2 (black/orange/orange); 6 strobe 3 (black/yellow/yellow); 8 strobe 0 (black/brown/brown); 7 and 9 unused. J6 and J7 sit right below the battery, so they often need re-pinning.

Systems

• Gottlieb System 1

Related tips

• Testing switch return buffers Z9 and Z28
• Switch strobes missing at Z8
• Test PROM switch actions
• System 1 switch matrix layout
• Slam and outhole switches sit outside the matrix
• Switch matrix dead after coil or GI voltage touched it
• Clamp diode mod to protect U5
• Logic-probing the switch matrix

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)