Test a 2N6427 (MPSA14) lamp matrix transistor with a meter
Steps
- Meter on diode test.
- Red lead on the middle leg.
- Black lead on the right leg: expect about 1.0 to 1.3 V.
- Black lead on the left leg: expect about 0.6 to 0.8 V.
- MPSA14 or NTE46 are substitutes.
Systems
Related tips
- Diode-test the lamp pre-drivers (2N6427/MPSA14)
- Lamp and switch matrix transistor positions on the CPU board
- Lamp matrix still wrong after replacing transistors: upstream parts
- Test a 2N6122/TIP41 lamp row transistor with a meter
- Lamp column still dead after a new TIP42
- Replace the TIP42 lamp column transistors with IRF9Z34N MOSFETs
- Driver board transistors and what they drive
- Replace burnt 3 watt lamp resistors with 5 watt
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)