Each switch works alone, but closing several switches in the same row or other columns gives false readings.
False switch readings only when several switches are closed
Cause: A switch diode has shorted. (An open diode, by contrast, only stops its own switch working.)
Checks
- Diode-test the switches involved.
Fix
- Replace the shorted diode.
Systems
Related tips
- 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
- Fit a replacement switch diode the right way round
- Testing CPU switch rows and columns with a diode and clip lead
- Row or column fault on the playfield
- Strange behaviour across a whole row or column from a switch diode
- Lamp lights twice or two lamps act as one
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)