A shorted coil means replacing its whole driver path
When a coil reads low, expect to replace the coil and its diode and every semiconductor between the coil and ground: any under-playfield transistor, driver board transistor and pre-driver. Also check the 74175 that feeds those transistors with the meter on diode test.
Systems
Related tips
- Coils or driver transistors run very hot
- Firing coils from CPU buffers Z6 and Z7
- Why System 1 coils lock on: the ground shift
- Lamp test can hold coils on for five seconds
- A CPU controlled coil does not fire
- Testing the 2N6043 coil drivers
- How many coils the driver board can fire
- Which driver transistor fires which coil
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)