Thread breakage
I just purchased a used Janome 1600P and was going nuts with thread breakage. I noticed in the manual that it suggests that if the thread breaks a lot to thread it through all three eyes of the pretension bar. I did that and have not had any more problems. Oh, and I also have to watch very carefully how I wind the thread around to get it into all three holes because sometimes I loop it and it forms a knot. I hope this helps.