Always check the coil diode when a driver transistor has failed
A broken diode on the coil itself is a frequent reason a Data East/Sega driver transistor fails. If you replace the transistor and leave the bad diode, the new transistor will fail the same way, so inspect or replace the diode on that coil every time.
Systems
Related tips
- Test the switch column drivers with a diode jumper
- Testing a coil diode
- Test each lamp column driver with a test lamp
- What the coil diode does and how a bad one shows up
- Test the switch row inputs with a diode jumper
- Switch row (return) circuit on the CPU board
- New batteries but still a memory error: check D25
- Testing the diode on a coil
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)