Meter transistor tests are not conclusive
A meter diode test checks a transistor at almost no load, so it is right about 95 percent of the time; MPS-U45s in particular can test good and still fail in the game. Before fitting a new driver, check its coil, or a shorted coil will kill it at once.
Systems
Related tips
- Spare transistors for System 1 boards
- Which driver transistor fires which coil
- Driver transistors Q1-Q4: relays and spare outputs
- How many coils the driver board can fire
- Testing the 2N6043 coil drivers
- Testing the Q45 2N3055 and its resistor
- Diode test of driver board 74175 chips
- Firing Q1-Q4 from the Z1 latch
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)