As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT DIVERTED AT FL390, RECEIVED CABIN ALTITUDE WARNING LIGHT AND HORN. PERFORMED AN IMMEDIATE EMERGENCY DESCENT TO 10000. NO CABIN OXYGEN MASKS DEPLOYED. NR 1 ENGINE PNEUMATICS WERE NOTED TO BE LOW AND THE LT PACK FAILED SINGLE PACK CONFIDENCE CHECK. MAINTENANCE FOUND SENSE LINE LEAKING TO PRSOV. REPLACED BOTH PRESSURIZATION CONTROLLERS AND UPPER PRESSURE RELIEF VALVE.