Check the switch matrix with a logic probe

Steps

• Power the game in attract mode or the switch levels test with CN8 and CN10 unplugged.
• Probe CN8 pins 1 to 9 (columns): each should pulse.
• Probe CN10 pins 1 to 9 (rows): each should read high.
• A column pin that does not pulse, or a row pin that is not high, points to that circuit on the CPU board.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Which switches are outside the switch matrix
• Resistor networks in the switch matrix
• Coin door test buttons bypass the switch matrix
• Switch row or column error: CPU board or playfield?
• Check the lamp matrix outputs with a logic probe
• Switch column (drive) circuit on the CPU board
• Switch row (return) circuit on the CPU board
• Test the switch column drivers with a diode jumper

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)