As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON INITIAL CLIMB, NOTICED THE CABIN DIFFERENTIAL PRESSURE WAS LOWER THAN STANDARD KNOWN VALUES. THE MAXIMUM DIFFERENTIAL PRESSURE THE ACFT WOULD HOLD WAS 3.6PSI. THIS IS A LARGE DEVIATION FROM NORMAL OPERATION AND FELT IT WAS PRUDENT TO RETURN TO DEPARTURE. RETURN WAS COORDINATED WITH ATC AND OPS AND WAS WITHOUT FURTHER EVENT. SEALED NUMEROUS AIRFRAME LEAKS AND REPLACED PRESSURE CONTROLLER IAW MM 21-30-10. OPS CHECKED GOOD IAW MM 21-30-00.