What was found
TAKEOFF WARNING HORN SONDED ON T/O ROLL FOR 3 SEC NO ABNORMAL SETTINGS OR INDICATIONS. PERFORMED GVI OF PARKBRAKE MICROSWITCH AFTER CLEAN AND LUBE W/ APPROVED PRODUCTS AND NO DEFECT NOTED. C/W FUNCTIONAL TEST OF THE TAKEOFF WARNING SYS IAW AMM 31-51-00-720-801. FUNCTIONAL CHECKS GOOD. REPLACED FDR W/ NEW FROM STOCK IAW AMM 31-32-01-000/400-801 AND HS NR31-0003. OPS CHECK OF FDR GOOD & FUNCTIONAL TEST OF ULB GOOD. ACFT OK FOR SERVICE. NOTE: FDR PN 980-4700-027 SN 12574 REMOVED IN SERVICEABLE CONDITION. RETURNED TO SERVICE.