MOSFET lamp column upgrade
The eight TIP42 lamp column transistors (odd numbers Q63 to Q77) can be replaced with IRF9Z34N MOSFETs, fitted the same way round. They need almost no drive current, so R149-R156 stop running hot; those resistors can then stay as they are (unless open) or be replaced with wire links or zero-ohm resistors.
Systems
Related tips
- Replace the TIP42 lamp column transistors with IRF9Z34N MOSFETs
- Tester LED check of the lamp columns
- Diode-test the lamp column and row transistors
- Logic-probe the lamp columns and rows
- Lamp matrix column test at 2J5 with Leon's code
- Photo: MOSFET lamp drivers with jumper wires
- A whole lamp row or column dead or stuck on
- How the lamp matrix runs 6.3 V bulbs on 18 V
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)