We have had thread breakage with ours. I was ready to torch the thing, but eventually all the planets aligned and now we rarely have a problem. Here are some of the things I check:
1) We use Connecting Threads essentials top and bottom. We have also had good luck with Maxi-Lock 100% polyester thread. It is marketed for sergers, but works great for quilting. We have also used invisible thread in the bobbin.
2) The tension discs at the top of the machine can get the tiniest spec of lint or thread and throw off your tension. Loosen your tension and floss your tension assembly with dental floss or a pipe cleaner. You can also take the whole assembly apart, but make sure you pay attention to the parts so you know how to put it back together.
3) One of my problems was threading the needle the wrong way. You have to thread toward the machine.
4) You have to have a bit of space between the take-up rail and the bed of the machine. If you can slide your fingers between them and just feel them on the top and bottom of your fingers you have perfect space.
I think there may be a couple of other things to check. If I think of anything else I'll post again. Let us know if you solve your problems.
Darren