Test a switch diode (fail-safe method)

Steps

• Turn the game off and set the meter to diode test.
• Black probe on the band, red on the other end: about 0.4 to 0.6 V.
• Reverse the probes: open (no reading).
• If it tests bad, cut one diode lead free of the switch and test again to be sure.
• Replace the diode if bad, or rejoin the lead if it was fine.

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)