Early System 11 CPU connector 1J9 was never used

Original System 11 CPU boards have a second switch-row header at 1J9 meant for opto switches. No game used it and it was dropped from System 11A boards onward.

Systems

• Williams System 11

Related tips

• System 11 switch matrix: connectors and chips
• System 11 CPU board connectors
• Find the short before refitting a repaired CPU
• Connector 1J8 switch column pins
• Connector 1J10 switch row pins
• Decide whether a phantom switch is in the playfield or the CPU board
• Bussed versus isolated resistor networks on the CPU board
• Row or column error: CPU board or playfield?

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell