What was found
AFTER T/O, GEAR SELECTED UP BUT NOSE GEAR FAILED TO RETRACT. EXTENDED GEAR SUCCESSFULLY USING ALTERNATE GEAR SYSTEM. NORMAL LANDED ENSUED, PINS INSERTED ON RUNWAY AND AIRCRAFT TOWED TO HANGAR. INSPECTED DOOR LINKAGES, OK. MAINTENANCE SUSPECT GEAR DOOR SENSOR. LEFT MLG DOOR SENSOR "TOO FAR" SENSOR ADJUSTED RETRACTIONS TO BE COMPLETED. ANOTHER EVENT, PILOT REPORTED LEFT MLG RED FOLLOWED BY LEFT MLG AMBER THEN BOTH EXTINGUISHED. LEFT MLG UPLOCK SENSOR REPLACED.