What was found
TAKEOFF WARNING HORN SOUNDED DURING TAKEOFF ROLL (UNDER 30 KNOTS) TRIM WAS IN T/O RANGE, CONTROLS NOT LOCKED CONDITION LEVERS MAX, FLAPS SET TO 10 DEGREE AND FLIGHT TAXI SWITCH IN FLIGHT. PERFORMED OPS TEST OF T/O WARN SYS IAW AMM 31-41-00-710-802, FUNCTIONAL TEST OF THE T/O WARN SYS IAW AMM 31-52-00-720-801. OPS TEST OF THE ADC & CAT 3 RETURN TO SERVICE IAW MTC 6341101. ALL OPS & FUNCTIONAL TESTS GOOD, NO FURTHER DEFECTS NOTED. ACFT REMAINS CAT 3, COCKPIT PLACARD REFLECTS CAT 3. RETURNED TO SERVICE. COULD NOT DUPLICATE.