The T-Rex head only ever moves to the left; in test, the control that should turn it right also turns it left. No fuses on the motor/shaker board are blown and the diodes test good.

T-Rex only turns left: cracked solder joints on the T-Rex relay board

Cause: Cracked solder joints on the relay board that drives the T-Rex motor direction. A first quick reflow didn't fix it; reworking the joints properly did.

Checks

• Check the fuses and diodes on the T-Rex motor board first.
• Inspect every relay pin and header joint on that board under a magnifier for ring cracks.

Fix

• Reflow all the relay and connector joints on the T-Rex relay board with fresh solder, then retest both directions.

Systems

• Data East CPU Version 3

Games

• Jurassic Park

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