As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A HEAVY MAINTENANCE VISIT, DURING COMPLETION OF A CABIN LEAK CHECK THE ALTITUDE WARNING HORN FAILED TO GO OFF WHEN THE CABIN ALTITUDE REACHED 12,000 FT. REMOVED AND REPLACED THE CABIN ALTITUDE SWITCH AND THE SYSTEM OPERATIONALLY CHECKS GOOD IAW DC10 MM 213303.