Fuse F5 blows as soon as a flipper button is pressed. After the shorted driver parts are replaced the fuse holds, but both slingshots stay dead even though their switches register; the pop bumpers work.

F5 blows on a flip, then slings dead: shorted drivers and a loose coil power wire

Cause: A slingshot driver stage had failed shorted: both the small pre-driver (2N4401) and the TIP122 driver. The dead slings came from a different fault: the heavy power wire on the coil supply chain had come loose at the right pop bumper coil because of a poor solder joint, leaving its bare end free to short.

Checks

• Test the driver transistors and pre-drivers for the coils on F5's circuit; replace any that are shorted.
• With the game on, check for coil voltage on both slingshot coils.
• Follow the coil power wire back along its daisy chain (through the pop bumper coils) for a loose or badly soldered joint.

Fix

• Replace the shorted 2N4401 and TIP122 (a 2N3904 was used for the 2N4401 here).
• Resolder the loose power wire properly at the pop bumper coil and insulate any bare ends, then retest the slings.

Systems

• Data East CPU Version 3

Games

• Last Action Hero

Related tips

• How a coil or flasher is switched: PIA to TTL to pre-driver to driver
• Three-stage drive for 50 V coils
• Solenoid driver transistor positions on the CPU and PPB boards
• A coil or flasher comes on and stays on at power-up
• Multiplexed L/R (A/B) banks and wire colours
• Flash lamp stuck on and melting plastics on L/R reversed games
• The solenoid L/R select relay and transistor Q29
• Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board

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