The reset coil for the back (top) drop target bank stays energised at power on, gets hot enough to melt its sleeve and smoke, even with the targets down and their switches open.

Back drop target reset coil locks on and melts its sleeve: shorted Q58

Cause: The drive transistor for that coil on the solenoid driver board (Q58, one of the large metal-can transistors) had shorted, holding the coil on. This game's three under-playfield transistors run the ball release, hole kicker and fire pit, not the drop banks.

Checks

• Turn the game off at once if a coil stays on.
• With the board out, test Q58 (and the other top-bank driver, Q57) for a short with a meter's diode test.
• Look for heat marks on the board around the transistor.

Fix

• Replace the shorted transistor and the burnt coil.
• Make sure the transistor's mounting screws are tight, and consider the usual ground upgrades on the driver board.

Systems

• Gottlieb System 1

Games

• Volcano

Related tips

• Coil stuck on that is driven through a playfield-mounted power transistor

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