On Volcano, Black Hole or Haunted House, one of the extra coils (kick-outs, ball release, drop target reset, trap door) locks on or fires by itself.

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

Cause: These coils are run by a lamp driver transistor on the driver board switching a PNP power transistor bolted under the playfield. Either transistor may have failed. Without a pull-up on its base, the playfield transistor can also drift on by itself.

Checks

• Test the playfield transistor with a meter on diode test (see the transistor test entry).
• Test the lamp driver transistor on the driver board that feeds it.
• Check whether the playfield transistor has a pull-up: a leg with two wires on it means one is fitted.
• Check the coil diode is not reversed.

Fix

• Replace the failed transistor(s).
• Add a 4.7k 1/4 W pull-up from the playfield transistor's base to +24 V DC if missing; on Black Hole replace any original 10k pull-up with 4.7k.

Systems

• Gottlieb System 80

Games

• Black Hole
• Haunted House
• Volcano

Related tips

• Adding the 4.7k base pull-up to playfield power transistors
• Haunted House trap door won't open
• Building a replacement SRC pack from discrete parts
• Haunted House driver board: which transistor runs which coil
• Black Hole driver board: which transistor runs which coil
• Test an under-playfield 2N5875/2N5879 coil transistor
• Black Hole: run the backglass motor only during a game (transistor method)
• Check every coil's resistance before first power-up

Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)