What was found
(CAN) HELICOPTER STARTED NORMALLY BUT WHEN THE THROTTLE WAS ADVANCED TO THE GATE (100 PERCENT NR), THE MAIN ROTOR STARTED OVERSPEEDING (400 RPM APPROX). THE THROTTLE WAS THEN PULLED BACK AND THE ROTOR SPEED DROPPED. WHEN THE THROTTLE WAS ADVANCED INTO THE GATE AGAIN, THE NR STARTED OSCILLATING BETWEEN 360 AND 400 NR WITH NO INPUT FROM THE THROTTLE OR COLLECTIVE. THE GOVERNOR WAS REPLACED AND THE PROBLEM WENT AWAY. (TC NR 20060605011)