As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SMF - AIR TURN BACK - AFTER TAKEOFF CREW REPORTED THAT THEY WERE UNABLE TO CONTROL CABIN PRESSURE, OUT FLOW VALVE WAS AT THE FULLY CLOSED POSITION AND HAD A VENT SKIN VALVE FAULT THAT WOULD NOT RESET. CREW RETURNED TO SMF AND LANDED WITHOUT FURTHER EVENT. MAINTENANCE REMOVED AND REPLACED THE SKIN AIR EXTRACT VALVE. OPEATIONAL CHECKS WERE GOOD.