Testing MPS-A13 and MPS-U45 driver transistors
Steps
- Meter on diode test; work on the component side. These read the same in and out of circuit.
- MPS-A13s are Q5-Q24 and Q33-Q44 (lamps); MPS-U45s are Q1-Q4 and Q29 (relays, pre-driver, two backbox lamps).
- Red lead on the middle (base) lead. Black on the left lead: about 1.3. Black on the right lead: about 0.7.
- Within 0.1 of those is good. Zero or no reading is bad, and 0.4-0.6 is probably bad.
- Compare with neighbouring transistors of the same type.
Systems
Related tips
- Which driver transistor fires which coil
- Driver transistors Q1-Q4: relays and spare outputs
- Spare transistors for System 1 boards
- How many coils the driver board can fire
- Diode test of driver board 74175 chips
- Early driver boards lack isolation diodes
- Testing the Q45 2N3055 and its resistor
- Firing Q1-Q4 from the Z1 latch
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)