A small coil in the drop target assembly is energised all the time and heats up as soon as the game is on. New diodes, a new coil, another driver board and a new CPU board don't help, and the coil also fires during the controlled lamp test.

Coil in the drop target assembly is always on: burnt trace on the solenoid driver board

Cause: The solenoid driver board had a burnt coil drive trace from earlier use in another game, connecting that coil's line where it shouldn't be.

Checks

• Note which coils fire in the controlled lamp test and in coil test; a coil that responds in the wrong test points to a cross-connection.
• Inspect the driver board traces for that coil's circuit for burns or bridges, and diode-test its driver transistor against its neighbours.

Fix

• Repair the burnt trace on the solenoid driver board (and any damaged parts on that circuit), then retest.

Systems

• Bally MPU AS-2518-35

Games

• Medusa

Related tips

• Bally -35: momentary solenoids all dead but fire when grounded: solenoid driver U3
• Pop bumpers fire nonstop after a solenoid expander swap: board jumper set wrong
• Kickout coil burns up in attract mode: driver transistor, resistor and the CA3081 at U3
• Arcing between J3 pins on the solenoid driver board and displays out
• Drop target coil fuse keeps blowing: shorted diode on the coil
• Coils go weak or the wrong coil fires mid-game: reseat the solenoid driver plugs
• Top lane gate never opens, even in solenoid test: failed driver transistor
• Backbox GI out and fuse F6 blowing: burnt rectifier J3 plug and a shorted bridge

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