As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURNBACK TO RFD FOR PRESSURE CONTROLLER PROBLEM, BOTH AUTO 1 AND AUTO 2 ARE SPIKING 200 TO 300 CABIN DIFFERENTIAL DURING CLIMB. REPLACED OVERHEAD CONTROL PANEL IAW AMM 21-31-01, OPS CHECKED NORMAL. IN ADDITION COMPLIED WITH FIM 21-30-00 AND AMM 21-30-00 PRESSURE CONTROL SYSTEM, OPS CHECKED NORMAL. (A)