What was found
CLT - LEVEL AT FL270, CREW REPORTED THE CABIN ALTITUDE WARNING HORN SOUNDED. CABIN ALTITUDE WAS AT 10,000 FEET AND CLIMBING. AT 14,000 FEET, THE OXYGEN MASKS DEPLOYED AUTOMATICALLY (FORWARD FLIGHT ATTENDANTS MASKS DID NOT DEPLOY). CREW DESCENDED AIRCRAFT TO 7,000 FEET AND OPERATED OUTFLOW MANUALLY AND WITH STANDBY NORMALLY. FLIGHT RETURNED TO FIELD AT CLT AND LANDED WITHOUT FURTHER INCIDENT. AIRCRAFT TAXIED TO THE GATE ON ITS OWN POWER. MAINTENANCE CONFIRMED CABIN PRESSURE CONTROLLER FAILED IN AUTO MODE. REMOVED AND REPLACED CONTROLLER PER MM 21-36-21. PERFORMED OPERATIONAL TEST PER MM 21-31-00. REPLACED OXYGEN GENERATORS AND PACKED MASKS. ACCOMPLISHED HULL LEAK TEST PER MM 05-51-91. CHECKS GOOD.