As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT THE ALTITUDE WARNING HORN SOUNDED. THE CABIN ALTITUDE WAS APPROACHING 11,000 FT & RISING. RAN THE QRH & CHECKED THE PANEL WHICH OFFERED NO RELIEF, THEN IAW THE QRH. WE DESCENDED TO 10,000'. SELECTED THE STANDBY MODE. STILL NO RELIEF. REMOVED AND REPLACED THE CABIN PRESSURE CONTROLLER AND CABIN PRESSURE CONTROL PANEL IAW AMM 21-31-010-4 AND 21-31-000-1-0 OP'S CHECK GOOD IAW MM 21-31-000-2.