As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOST CONTROL OF CABIN PRESSURIZATION AT FL 230. SYSTEM REVERTED TO STBY MODE BUT STILL UNABLE TO CABIN ALT BELOW 1000 FT. OUTFLOW VALVE COULD BE SEEN SWINGING OPEN/CLOSED WITH EXPECTED SWING IN CABIN VSI RATES. REPLACED AUTO PRESS CONTROL PANEL. TESTS NORMAL PER M/M 21-31-000-501. RAN ENGINE AND PRESSURIZED A/C NORMALLY ON ENGINE AIR.