As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT LEVEL OFF AT 37,000 ALTITUDE WARNING HORN SOUNDED AND CABIN ALTITUDE CLIMBING TO 10,000. DESCENDED TO MAINTAIN 10,000 CABIN ALTITUDE AND SELECTED MANUAL AC & DC WORKED OK NO FAIL LIGHT. FOUND FWD OUTFLOW VALVE STUCK OPEN. REPLACED VALVE. ALSO, OVHD PANEL WOULD NOT TEST PROPERLY. REPLACED PANEL.