If you haven't had the problem before it's probably the thread or needle. I had a Brother 1500 and it broke three times because of the same thing. The repairman didn't know enough to tell me not to use bobbins with holes around it. A tech found the problem. Holy bobbins will cause a lot of damage. He explained but I forgot. Always use the type of bobbins that came with the machine. I bought a Juki and was told never to use any bobbin not made for that model machine. Both are great machines.