A low resistance coil points to a bad driver transistor
A coil that locked on overheats, its enamel burns and its resistance falls until it shorts and blows a fuse. When you find one, also check the driver transistor that fires it.
Systems
Related tips
- Driver board transistors and what they drive
- Coil locks on and new transistors don't help: a failed 7408 on the driver board
- Spare transistors for driver board and power supply
- Coils 1-8: connector, transistors, PIA pin
- Coils 9-15 and coin lockout: connector, transistors, PIA pin
- Coil still locked on with good transistors and gate
- How a coil is switched on
- Coil has power and wiring is good but still dead or locked on
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)