Switch row (return) circuit on the CPU board
The rows come in on CN10, through the 560 ohm x 8 network RA16, 1k resistors (R116 to R133 on most boards, drawn on the schematic as two 1k x 4 networks RB5 and RB6), diodes D26 to D33 (1N4004), the 4011 chips at 5J and 6J, and into pins 2 to 9 of the PIA at 8H.
Systems
Related tips
- Test the switch row inputs with a diode jumper
- One switch row dead: parts to check in order
- Test the switch column drivers with a diode jumper
- Whole switch column dead after working under the playfield
- Always check the coil diode when a driver transistor has failed
- Test each lamp column driver with a test lamp
- New batteries but still a memory error: check D25
- False switch readings only when several switches are closed
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)