What was found
AFTER TAKEOFF, CREW ATTEMPTED TO RETRACT LANDING GEAR. GEAR CAME UP PARTIALLY AND STOPPED. CREW SELECTED GEAR DOWN, NO RESPONSE. CREW EXTENDED LANDING GEAR BY FOLLOWING ABNORMAL GEAR PROCEDURES. OBTAINED THREE GREEN, NO IN TRANSIT LIGHT. PROCEEDED TO RETURN TO AIRPORT AND LAND, NO FURTHER INCIDENTS.UPON INSPECTION THE LANDING GEAR ACCUMULATOR WAS FOUND TO BE AT ZERO PRESSURE. PER MAINTENANCE MANUAL, THIS CAN CAUSE THIS ISSUE. ACCUMULATOR WAS REPLACED AND CHARGED PER MANUAL, LOCAL TEST FLIGHT COMPLETED, NO FURTHER ABNORMAL ISSUES.