I have two garage doors. One works fine, other side opens partially then closes. After looking closely, one that opens partially has excess cable - about 6" worth (on each side of door) . I can't believe BOTH cables for door stretched THAT much. Where did excess cable come from? Thoughts? Is there a spring that assists the lifting? or is it all done by the motor? 1st pic is left side of door, 2nd is right side of door, 3rd is normal other door-RT side.