What was found
DURING CLIMB THE LOWER YAW DAMPER LIGHT ILLUMINATED BRIEFLY AND THE AIRCRAFT WAS DIFFICULT TO CONTROL IN HEADING. SLOWED AIRCRAFT TO 270 KNOTS AND TURNED OFF LOWER YAW DAMPER BUT AIRCRAFT WAS STILL DIFFICULT TO CONTROL IN HEADING. AIRCRAFT DECLARED AN EMERGENCY DUMPED 20,000 LBS OF FUEL AND RETURNED TO JFK AND AFTER LANDING EIGHT TIRE FUSES BLEW. REPLACED UPPER AND LOWER RUDDER POWER CONTROL UNITS BOTH YAW DAMPER COMPUTERS AND EIGHT TIRE ASSEMBLIES. OPERATIONAL CHECK GOOD.