As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THRU FL340 THE CABIN ALT WARNING ILLUMINATED WITH THE ASSOCIATED HORN. CREW DONNED OXYGEN MASKS & REQUESTED A LEVEL OFF, FOLLOWED BY AN IMMEDIATE DESCENT. EMER WAS DECLARED WITH CTR. CABIN NOTICES WERE TURNED ON & PAX OXYGEN MASKS AUTO DEPLOYED. ALL APPLICABLE CHECKLISTS WERE COMPLETED. ACFT LANDED SAFELY & NO PAXS WERE INJURED. PRESSURIZATION SYS WAS MEL'D IAW MEL 21-30-3. ACFT RETURNED FOR TROUBLESHOOTING OF PROBLEM. NO PAXS WERE ON THE RETURN LEG.