What was found
98-0100, AT FL290 CREW RECEIVED AN ECAM WARNING OF MAIN DECK SMOKE WARNING. CREW DONNED 02 MASK AND FOLLOWED AFM PROCEDURES. NEVER DID SMELL SMOKE. DECLARED PRECAUTIONARY AND RETURNED TO AIRPORT. T/S SYSTEM PER TSM, ALL DETECTORS TESTED GOOD. BITE TEST OF ALL THREE MAIN DECK SMOKE DET CTL UNITS, CHKS GOOD. RAN NR 2 ENG AND NR 2 PACK, OPS CHK NORMAL. NO INDICATION OF SMOKE OR FIRE DAMAGE NOTED. ACFT RETURNED TO SERVICE. REMOVAL AND REPLACEMENT OF ALL THREE MAIN DECK CARGO COMPT. SMOKE DETECTOR CONTROL UNITS PRECAUTIONARY.