What was found
SHORTLY AFTER TAKEOFF OF FLIGHT, THE CREW WAS UNABLE TO RETRACT THE GEAR. THE CREW PERFORMED AN AIR-TURN-BACK. MECHANIC INSPECTED THE SYSTEM AND REPLACED THE MLG HANDLE/SWITCH BUT OPS CHECKS WERE STILL BAD. MECHANIC REPLACED THE GROUND SERVICE VALVE AND PERFORMED A GEAR SWING, WITH NO FURTHER DISCREPANCIES NOTED, AC WAS RETURNED TO SERVICE. (K)