All thread breaks? Or just the spool you have on now? Also try running a couple lines of sewers aid down the spool/cone. It will work it's way down the thread path & help lubricate anything causing friction.
Is the machine on a quilting frame?
Floss the thread path with dental floss. That's a trick they use on embroidery machines. Watch the floss as you pull it through and see if it struggles to get through a particular spot or gets roughed up in a certain area.
I have had my needle just barely grazing the side of the hole in the single stitch plate causing it to fray so I had to move it over just a smidge. I have also had it rub on the foot causing fraying of the top thread & breaks.