What a bad switch diode does

Each playfield switch carries a 1N4004. Shorted diodes are uncommon, but one makes every switch in its row or column act oddly. An open diode just stops that one switch registering.

Systems

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

Related tips

• Test a leaf switch diode in place
• Test the switch column drivers with a diode jumper
• Test the switch row inputs with a diode jumper
• Fit a replacement switch diode the right way round
• Which switches are outside the switch matrix
• Use a real ball in the switch test
• Clearing a switch from the power-on switch report
• A single switch does not register

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