As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: ON TAKE OFF TO ABOUT 20,000' THE PRESSURIZATION V/S HAD WILD / ERRATIC SWINGS BETWEEN 50-1000 FPM CABIN V/S STARTED STABILIZE TO NORMAL ABOVE 20,000' ACTUAL PRESSURIZATION ISSUE, NOT JUST AN INDICATION PROBLEM. REPLACED CABIN PRESSURE CONTROLLER AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 21-31-34.