As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING AN INSPECTION OF THE BLEED AIR SYSTEM, THE CHECK VALVES WERE FOUND TO BE INOPERATIVE DUE TO PARTS MISSING MOST LIKELY DUE TO AGE. THE CHECK VALVES WERE REPLACED WITH SERVICEABLE CHECK VALVES. IT MAY BE NECESSARY TO COMPLETELY DISASSEMBLE BLEED AIR SYSTEM CHECK VALVES DURING DETAILED INSPECTIONS TO PREVENT ANY FURTHER MALFUNCTIONS.