EE WAS ASSIGNED TO REMOVE THE BELT TENSION BY LIFTING THE COUNTERBALANCE OF CONVEYOR BELT. EE POSITIONED THE CRANE EAST OF BELT. MAINTENANCE EE'S STARTED SETTING UP THE BELT & HOOKING THE SLIN GS TO THE CRANE & THE COUNTERBALANCE. THE CRANE STARTED LIFTING THE COUNTERBALANCE W/O ANY DIFFICULTY, THEN THE BOOM TURNTABLE STARTED RIPPING APART, EE JUMPED FROM THE CRANE & WAS INJURED.