Hello there, I have a few bernina records one with the oiling points in red the other unmarked, recently I had difficulty with tension most times I reread the machine, check I have a new needle that matches the fabric I am sewing and then adjusting the tension dial so that it isn't picking up unevenly, that is is it the top or the bottom that is most tight?
I have had to on occasion adjust the bobbin casing tension but only after all else has failed.