A meter test of a transistor is not conclusive
A diode-mode test checks a transistor at almost no load, so it catches about 95% of failures. MPS-U45s in particular can test good and still fail under load in the game.
Systems
Related tips
- Test the driver transistors while the board is out for the ground mod
- What the System 80 driver board transistors drive
- System 80 driver board transistor types
- Relay and coin counter transistors on the driver board
- Some 80B driver boards use the coin counter transistors
- Test driver board outputs by grounding transistor tabs
- Driver board transistors that look stuck on in a test fixture
- Coils lock on and burn because of the Gottlieb ground fault
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)