A couple of minutes into attract mode the right VUK coil locks on and burns, and its driver Q3 on the power board is found shorted. It works on the bench with a test ROM and coil tester, and in coil test.

Right VUK locks on in attract and keeps killing Q3: replace Q42 and its pre-driver

Cause: The MPU's Q42, which switches Q3 on, and its pre-driver were failing intermittently even though they tested good out of circuit, so Q3 kept getting turned on and destroyed.

Checks

• When a big driver transistor shorts, test the small transistor that drives it, and the coil, coil diode and fuse.
• Check any flashers sharing the same driver for the wrong bulbs (for example LEDs in place of 906 bulbs).
• If Q3 keeps failing with everything testing good, suspect the driving transistor anyway.

Fix

• Replace Q42 and its pre-driver on the MPU, along with the shorted Q3 and the damaged coil.

Systems

• Data East CPU Version 3

Games

• Jurassic Park

Related tips

• How a coil or flasher is switched: PIA to TTL to pre-driver to driver
• Flipper sometimes stays up until power off: broken coil diode
• Replace the pre-driver along with a failed driver
• Ball launch, laser kick and VUK dead: missing transistors on the playfield power board
• Quick test for shorted TIP122/TIP102 drivers
• 50 V coils use PPB TIP36c transistors, pre-driven from the CPU board

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