How do I fix the tension on a 140s smarter by PFAFF sewing machine?

The bobbin stays fixed and releases thread under bobbin tension. The part that moves is the hooked arm that is around the bobbin. This is disconnected when you are in bobbin winding mode, so make sure you are in sewing mode. Here is your manual

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We have 4 Pfaff 545 manuals available for free PDF download: Instruction Book, Instruction Manual. Pfaff 545 Instruction Book (33 pages).

Look very closely at your sample stitching and determine which thread (top or bobbin) is looping and which is breaking. That will narrow down where the problem exists.

A top thread that loops and makes thread "barfs" under the fabric is generally an upper thread tension problem.
Try: Remove the top thread. ALWAYS RAISE the presser foot and rethread from the beginning. Set the upper tension to the midway point (probably will need to tweak this tension depending on your machine).

Sewing Lesson 10 How to Fix Tension on Your Sewing Machine

Understanding Thread Tension Threads

Sewing Machine Tension

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What tension problem are you having? You can adjust the top thread tension in the tools menu normally on most auto tension models. The bobbin tension is adjusted by the tension spring screw.

Support site with phone number
http://www.pfaff.com/en-US/Support-and-Updates/Support

Machine Support

The tension setting adjustment is found in the tools menu

if you can take the pfaff back and tell them what its doing and have them fix it or get another sewing machine..

This is usualy a thread tension problem. Adjust the upper thread tension first. If tightening the upper thread tension doesn't work, then adjust the bobbin holder (lower thread tension) check with the user manual for your specific machine for the correct procedure.

If the thread is looping underneath, you're top tension may be too loose or the thread may not be in the take-up lever. If it's looping on top, double check that the thread is in the bobbin tension or that the bobbin tension isn't too loose.

Many users also reported similar bobbin tension adjust problems. But do you know it can be fixed by yourself? I suggest you to order the following product:
Sewing Machine Repair Guide
It's a professional repair guide written by an expert. Besides PfaFF sewing machine, you can learn how to repair other brands of sewing machine as well. The author claims that you can earn money after you had learned the repair skills!
Good luck.