Coils or driver transistors get very hot; coils may stick on or overheat.
Coils or driver transistors run very hot
Cause: Solenoid ground rising above logic ground, so drivers partly conduct all the time.
Fix
- Do all the ground modifications.
Systems
Related tips
- A shorted coil means replacing its whole driver path
- 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
- Which driver transistor fires which coil
- Testing the 2N6043 coil drivers
- How many coils the driver board can fire
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)