Try just adjusting the upper tension to a lighter setting. Also, sometimes just rethreading the upper thread and bobbin thread through the bobbin casing will work. Perhaps there is something wrong with just the one bobbin....try another bobbin..are they prewound or did you wind yourself? Try another design...perhaps it's the way the design was digitized? Just trying some suggestions here...Good Luck!

First try to clean all your bobin area out real good and floss your bobbin tension on the bobbin case with reguler sewing thread or un waxed dental floss. You may have a wee piece of thread caught in the bobbin tension.

It seems to me I have heard of this problem with this machine by others tha t have it so you may want to have a machine Tech check it out for you.

I Had this problem With Brother 4000D when I tried A different make of bobbin thread,I would try as cutie eastwitch says,Hope its a simple problem.

Just had that problem last week. I was not using the correct thread on my bobbin(I don't use the same for bobbin)I messed up some kitchen towels. Had thread all snarly on back.Out of 20 bobbins 1 was wrong size. One guess which bobbin I was using?No I did not want to mess the tension so I left that alone.Perfect now.

You might try a new needle as dull needle can cause thread problems in a design.
Change needles often!

Monica, I don't have a Brother PE700 - but by now - I am hoping you have your situation resolved or have taken it into the shop. Please let us know - how you resolved your bobbin tension troubles - it might help another down the line.

Monica, I have a PR 600 and in the handbook it deals with tension issues, both on top and in the bobbin.
I agree with the others, first do the simple things. Change thread, go back to a thread that worked before, and general maintenance.
Don't get drastic! If you cannot fix it simply then bring it to the shop. I understand it is costly, but this may be a solution too. ! Good luck, let us know
Hugs, Bonnie