I have been having problems with my brother machine also (thread breaking). Since before Christmas it has been in and out of the repair shop (the machine is a little over 1 year). One time I was told that the housing for the bobbin was bent. It was replaced. Since that it worked a couple of hours then threads breaking again!
Brought it back and forth 3 more times. During one of those times 2 circuit boards were replaced! Each time I was told it worked in the shop but when I get it home it doesn't work. Finally I brought it to another place to get repaired. I am now told it is some plastic part that is cracked. The part is being ordered and then I will see????