A coil locks on and burns, and replacing the transistors in its circuit makes no difference.

Coil locks on and new transistors don't help: a failed 7408 on the driver board

Cause: The 7408 gate that drives those transistors had failed, with floating output pins.

Checks

• With a logic probe, check the 7408 inputs and outputs for that coil and compare with the gates for working coils.
• Check the 40-pin board interconnect has been replaced, a known weak point on these games.

Fix

• Replace the faulty 7408 (fitting a socket), then check the coil, diode and transistors again before powering up.

Systems

• Williams System 6 / 6A

Games

• Gorgar

Related tips

• Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board
• A low resistance coil points to a bad driver transistor
• Coil still locked on with good transistors and gate
• Driver board transistors and what they drive
• Spare transistors for driver board and power supply
• Coils 1-8: connector, transistors, PIA pin
• All coils or lamps lock on at power-up
• Coils 9-15 and coin lockout: connector, transistors, PIA pin

Source: Pinball Repair help group!! (Facebook group)