Finding which transistor drives a lamp
Steps
- Note the wire colour on the failed lamp's socket.
- Game off: find that colour on the driver board bottom-edge connectors.
- With the meter on continuity, hold one probe on that pin and touch the right leg of each transistor until it beeps.
- Confirm with the game on by grounding that leg with a clip lead; the lamp should light.
Systems
Related tips
- How CPU-controlled lamps are driven
- No CPU controlled lamps light
- Testing a CPU lamp circuit by grounding its driver
- Groups of four lamps or single lamps misbehaving
- Spare transistors for System 1 boards
- Which driver transistor fires which coil
- Meter transistor tests are not conclusive
- Driver transistors Q1-Q4: relays and spare outputs
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)