Coin door test buttons bypass the switch matrix

The service buttons wire straight to CN14 on the CPU board, and the diagnostic button is tied to the processor's NMI line. You can therefore reach the tests even when a short has taken out the switch matrix.

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
• Check the switch matrix with a logic probe
• Resistor networks in the switch matrix
• Switch row or column error: CPU board or playfield?
• 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
• Test the switch row inputs with a diode jumper

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