As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 19 - AFTER TAKEOFF, AC CABIN PRESSURIZATION BEGAN TO CLIMB. AUTO CABIN PRESSURE SYSTEM WAS ON MEL, ACFT WAS IN STANDBY MODE. UNABLE TO CONTROL PRESSURIZATION IN STANDBY AC AND DC MODE. FLIGHT RETURNED TO PIT WHERE LANDING WAS WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED OUTFLOW VALVE AND CABIN PRESSURE CONTROLLER. REF 95ZZZZ231.