What was found
AFTER TAKEOFF, ENROUTE, CABIN PRESSURE BEGAN TO CLIMB WITH ALTITUDE. FLIGHT WAS LEVELED OFF AT 2500 FEET WHEN A FLIGHT ATTENDANT REPORTED THAT THE AFT ENTRY DOOR HAD POPPED OPEN. FLIGHT RETURNED TO FIELD AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE FOUND THE AFT ENTRY DOOR CONTROL ROD OUT OF ADJUSTMENT. ADJUSTED CONTROL ROD AND RESENT DOOR LOCKING PRESSURE. OPERATIONAL CHECK OF DOOR GOOD.