As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WOULD NOT PRESSURIZE AFTER TAKEOFF. FLIGHT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. MAINTENANCE TESTED SYSTEM AND DISCREPANCY COULD NOT BE DUPLICATED ON GROUND. REPLACED CABIN PRESSURE CONTROLLER AND AMPLIFIER AS A PRECAUTION, OPERATIONAL CHECK NORMAL.