Hello, We bought two units in 2001. One unit, recently experiencing intermit direction changes during operation. Then a few days ago, quit in mid opening. The motor works but the door is going in neither direction ...not up or down. Almost sounds like the chain might have jumped out of place or is it possible a gear/chain is striped. Can fix ourselves or do we need to call in a service person ? Cambridge, Ontario. Any help would be appreciated ? Thank you !