I have a Pfaff 2170. Today I set it up for embroidery and started a sample - thank goodness it wasn't my 'real' fabric! BIRD'S NEST.

Instead of doing any more embroidery, I decided to test the machine with regular sewing. The sample showed terrible tension - top thread pulling to the bottom.
I reset the tension every way I could think. It remained the same when I sewed no matter how it was re-set.
I made sure the foot was in the correct position.
I took out the bobbin and made sure I put it back correctly.
I rethreaded the needle.
I took out the needle and put it back in.

No matter what change I made, the tension remained the same.

I called my Pfaff dealer and found out she's no longer in business. I went on-line and found out the nearest Pfaff dealer is in NY, and I'm in CT. I'll call them Monday - I'm too upset today!!!!!!!!!!!!