As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ACFT PERFORMED AN ALTERNATE LANDING GEAR EXTENSION. TROUBLESHOOTING IN PROGRESS. MX PLUGGED AN EXTERNAL POWER CART TO THE ACFT IN COCKPIT 3 GREEN LIGHTS WERE ON. UNABLE TO CLOSE NOR OPEN GEAR DOOR. LG SELECTOR REPLACED GEAR SWINGS PERFORMED.