THE PILOT STATED THAT, 'I LANDED IN AN OPEN UNPOPULATED AREA FOR THE MECHANIC ... TO MAKE ADJUSTMENTS ON THE MAIN BLADE (WE WERE TRACKING AND BALANCING THE BLADES). I NEVER SHUT THE ENGINE DOWN. I DISENGAGED THE CLUTCH. AFTER THE ADJUSTMENT WAS MADE, I ENGAGED THE CLUTCH AND BROUGHT IT UP TO FULL POWER WITH ALL THE CHECKS BEFORE LIFTING OFF. EVERYTHING CHECKED OUT OK. I HAD LANDED INTO THE WIND AND DEPARTED INTO THE WIND. ABOUT 25-30 FEET HIGH THE HELICOPTER SOUNDED LIKE IT WAS LOSING POWER AND VIBRATION WAS FELT. A QUICK LOOK REVEALED LOSS OF BOTH TACHS (TACHOMETERS) OF ROTOR AND ENGINE. I LOWERED THE COLLECTIVE AND ADDED MORE POWER WITH NO EFFECT. UPON LANDING THE HELICOPTER ROLLED OVER ON ITS LEFT SIDE. NO CONTROLS WERE EFFECTIVE DUE TO LOSS OF (ENGINE/ROTOR) RPMS.' THE HELICOPTER HAD BEEN MOVED PRIOR TO OFFICIALS ARRIVING ON SCENE. LATER INSPECTION REVEALED NO EVIDENCE OF A MECHANICAL MALFUNCTION OR FAILURE OF ANY SYSTEM.