Driver board transistors and what they drive
TIP120 transistors (fed by 2N4401 pre-drivers) drive the solenoids. TIP42s drive the lamp matrix columns and 2N6122 (or TIP41) transistors the lamp matrix rows. Small 2N6427s give lamp matrix overcurrent protection, and 2N5060 SCRs are the lamp matrix pre-drivers. Meter diode tests on these are a good guide but not proof.
Systems
Related tips
- Spare transistors for driver board and power supply
- A low resistance coil points to a bad driver transistor
- System 6 and System 7 driver boards can be swapped for testing
- Hyperball driver board is unique
- Coil locks on and new transistors don't help: a failed 7408 on the driver board
- Test a 2N4401 pre-driver with a meter
- Leon's code with the driver board attached
- Add a blanking LED to a driver board
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)