granny64,
I had problems with the top tension changing on our 401A while we were sewing with it. The tension assembly is very similar to the 201s so what I did for ours should work with yours too. The adjusting nob on ours was too loose and would just vibrate looser as we sewed.
First go here: {
http://www.tfsr.org/publications/tec...machine_manual } and study how the tensions work. There is detailed instructions on how to R&R, repair and adjust them.
That said all I had to do with ours was spread the fingers of the split shaft apart to tighten up the fit of the numbered dial. That way it doesn't move unless we adjust it.
To do that you have to take it apart, that's why the TFSR site.
Joe