A maintenance employee was helping to troubleshoot a fault in the hoist on a bottle line de-palletizer. A broken sprocket needed to be removed in order to level the hoist. The machine was locked out/tagged out and the cover of the chain and sprocket was then removed. The employee used a pry bar to pull back and relieve the tension on the chain that was attached to the sprocket, in order to guide the sprocket out with his left hand. The pry bar slipped out and the chain snapped back, which caused the sprocket to shift. The employee's left middle finger was pinched between the chain and sprocket and the fingertip was amputated.