What was found
THE ACFT WAS ON A LOCAL TRAINING FLIGHT. AFTER TAKEOFF THE LANDING GEAR WAS VERY SLOW TO RETRACT. THE ACFT RETURNED TO BASE. MX INSPECTED THE ACFT AND FOUND NO VISIBLE DISCREPANCIES. THE ACFT WAS JACKED. WHEN ATTEMPTING TO RETRACT THE LANDING GEAR THE NOSE WOULD RETRACT, BUT THE MAINS WOULD NOT UNLOCK FROM THE DOWN POSITION. THE LANDING GEAR CONTROL VALVE WAS CHANGED AND AN OVERHAULED UNIT WAS INSTALLED. STILL NO CHANGE. AFTER MORE TROUBLESHOOTING THE LANDING GEAR CONTROL HANDLE WAS CHANGED. STILL NO CHANGE. AFTER MORE TROUBLESHOOTING ANOTHER LANDING GEAR CONTROL VALVE, ALSO FRESHLY OVERHAULED, WAS INSTALLED. THIS FIXED THE ISSUE. FIFTEEN GEAR SWINGS WERE PERFORMED BY MX, AND A TEST FLIGHT WITH FIVE GEAR SWINGS WAS ACCOMPLISHED SUCCESSFULLY.