How Do I Get Clock To Work?

I have acquired a West German wall clock with chains and weights. The chain for the chimes works ok . The other chain will not move at all even if I pull it. There is an aluminium crescent-shaped 5" long piece attached to centre top of movement which moves from side to side and when I move this by hand the chain moves but when released the chain will not move. I am not sure if this piece should be attached somewhere else on the clock. It seems to me to act like a pendulum but it doesnt hang down as a pendulum does, it goes up. Your help would be greatly appreciated.