As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE AIRCRAFT PRESSURE COULD NOT BE CONTROLLED IN AUTO, ALTERNATE, OR MANUAL AFTER TAKEOFF FROM MEX. THE OXYGEN MASKS WERE DEPLOYED AND THE AIRCRAFT WAS RETURNED TO MEX WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE AFT OUTFLOW VALVE AND BOTH CABIN PRESSURE CONTROLLERS. MAINTENANCE FOUND THAT THE 02 GENERATORS IN LAVS AND SEAT ROWS 1AB, 3AB, 3EF, AND 19L HAD NOT FIRED. ALL O2 GENERATORS WERE REMOVED AND REPLACED AND THE O2 MASKS WERE REPACKED.