As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW UNABLE TO CONTROL CABIN ALTITUDE IN CABIN ALT AUTO 1. CABIN ALT AUTO 2 ON ACTIVE DEFERRAL-38148 MEL CAT C. AIR TURN BACK TO DEPARTURE STATION WITH EMERGENCY DECLARATION. LANDING UNEVENTFUL WITH NO ADDITIONAL PRECAUTIONARY ACTIONS. ON ARRIVAL AIRCRAFT GROUNDED FOR UNSCHEDULED MAINTENANCE. REMOVED AND REPLACED #1 CABIN PRESSURE CONTROLLER IAW AMM 21-31-02. OPERATIONAL CHECK GOOD. AIRCRAFT RELEASED TO SERVICE.