Top tension problems can be the result of thread or lint being trapped in the tension discs. First try running a thin line (like fishing line or unwaxed floss) through the tension discs to see if any lint comes out. If cleaning does not work, then try removing the top cover of the embroidery machine to expose the tension discs for a more thorough cleaning. The video below shows how to service a Brother embroidery machine and clean the tension discs.
How to fix clean the top tension discs:
If cleaning the tension disc does not fix the problem, then try cleaning the tension spring and removing any thread caught there.
Check out our article on Checking the Upper or Lower Thread Error Messages.