An employee was troubleshooting a problem on the screen deck of a batch plant. To determine if the problem was mechanical or electrical, the employee locked out the system and tried to jog the belts by hand. When he tugged on the belt, the eccentric shaft counterweight swung down, driving the belt toward the sheave. The tips of his right ring and little fingers were pinched between the belt and the sheave, and the ring fingertip was amputated just above the first knuckle.