As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - AFTER TAKEOFF AUTO PRESSURE CONTROLLER WENT TO MANUAL MODE AND IT WOULD NOT CONTROL THE CABIN PRESSURE. DURING DESCENT IT BEGAN TO WORK. RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. MAINTENANCE REPLACED THE NR 2 SAFETY OUTFLOW VALVE. OPERATIONAL CHECKS GOOD AIRCRAFT RETURNED TO SERVICE.