From what you describe the problem is with the release mechanism for the top tensioner. It's either behind the face plate or if you have the version with the tensioner closer to the top lid, it's under there. I would open the top lid and the face plate, lift the presser foot lever up and down and inspect all the parts involved from behind the lever to the top tensioner. There is a pin in the split screw (holding the enitre assebly of spring, dial and plates) that doesn't get pushed out properly. When presser bar lever is up the plates should be loose, when down they stay firmly together.
Last edited by Mickey2; 08-10-2016 at 04:38 AM.