What was found
CONFIGURATION FOR TAKEOFF WAS FLAPS 15, ALL INDICATIONS WERE NORMAL UNTIL WE SET TAKEOFF THRUST AND GOT A VERBAL FLAP WARNING AND A WHITE FLAP BOXED WARNING ON THE NUMBER 3 DU. TAKEOFF WAS REJECTED AT 40 KNOTS. REMOVED AND REPLACED STANDARD ELECTRONIC MODULE IAW AMM 28-41-92-4 OPS CHECKED GOOD. REMOVED AND REPLACED BOTH FMC'S IAW AMM 34-63-01-4. GREEN BAND PRESENT AND ALL TAKEOFF WARNING CHECKS OPERATE NORMALLY IAW AMM 27-02-01-5.