As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUTO CABIN PRESSURIZATION FAILED AFTER TAKEOFF. CABIN PRESSURE WENT TO FULL INCREASE RELIEVING PRESSURE AT 8.06 PSI AND SHOWING NEGATIVE CABIN ALTITUDE. NORMAL CABIN PRESSURE WAS REGAINED USING MANUAL CONTROL BUT VERY DIFFICULT TO MAINTAIN. FLIGHT RETURNED TO ATL AND LANDED WITHOUT INCIDENT. REPLACED CABIN PRESSURE AMPLIFIER. OPERATIONAL CHECK OK ON GROUND. AIRCRAFT RETURNED TO SERVICE.