What was found
UNKNOWN BURNING ODOR COMING FROM AIR VENT OVER FORWARD FA JUMPSEAT. CHECKED CEILING AREA ABOVE ENTRY. NO ODORS PRESENT & NO ANOMALIES FOUND. OPS SAFETY VIDEO & CHANGED LIGHTING SCHEMES WHILE RUNNING PACKS & WITH RECIRC FANS ALONE. ALL OVENS & AFT CHILLER OPERATING. COULD NOT DUPLICATE ODOR. GAINED ACCESS TO MIX BAY. NO ODORS NOTED. DISCONNECTED & RECONNECTED RECIRC FANS. START, STOP & OPS SMOOTH. FILTERS HAVE DUST BUILD UP. NO ODORS NOTED IN AVIONICS BAY. VERIFIED ALL C/B'S CLOSED ON P91 & P92 PANELS. CHKD E11 & E6 RACK UNITS IN AFT CARGO BAY. NO ODORS NOTED. REPLACED BOTH LT & RT RECIRC FILTERS IAW AMM 21-25-01/401. NO FAILED UNITS OR SUSPECT ITEMS SHOWING ON CURRENT OR EXISTING FAULTS. ACCOMPLISHED 10 MIN IDLE RUN BOTH ENGS WITH ALL BLEEDS & BOTH PACKS RUNNING IAW FIM 21-00 TASK 830, STEP Q. NO SUSPECT ODORS GENERATED THROUGHOUT CABIN.