As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN ALTITUDE HORN WENT OFF, CLIMBING THRU 30K. CABIN ALTITUDE LIGHT ALSO ON CONTROLLABLE IN MANUAL. EMERGENCY DECLARED. REMOVED AND REPLACED NR 1 CABIN PRESSURE CONTROLLER IAW AMM 21-31-00 AND TESTED, SYSTEM TESTED OK, NO FAULTS NOTED.