answers
To answer some of your questions....
I oil the machine according to the booklet from Kenquilt. It is the bottom of the quilt that usually has problems. Primarily tension problems on the back, but also thread breakage is pretty common. Have tried all thread from Coats and Clark to Gutterman machine quilting thread. No formal training on using machine. Have sewn all my life, not to say I couldn't learn more (obviously). Normally on a sewing machine, once the tension is ok, it is ok unless you are sewing something considerably thinner/thicker. Maybe my repair people have not been so good?? How does a shop fix it and test it when I take it in without the frame??