I have a pfaff grand quilter and have used it to do six quilts and has worked great but the last quilt i did the top thread kept breaking every few inches i have tried everything but in the end took it in for full service got it back and still the same it seems to be getting caught in the tension knob also it has started to skip a lot of of stitches and has one long stitch every know and then i am trying to fix as i go because i can not get anyone to come and have a look as they are to busy i am wondering if the stitch regulator might have something to do with it as in the shop with the foot on it works good. the shop i took it to will not help he had my money.

Be sure to use a darning foot (or free motion quilting foot).
Use a brand new sharp needle, ie top stitch, embroidery, or microtex work well.
Check that the thread, needle, and fabric are compatible--Caution, the needle eye should be the right size for the thread weight.
AVOID old or bargain bin thread!
Be sure to drop or cover the feed dogs.
If your machine has it, use the needle down feature.
You may need to adjust the tension for FMQ--I have to tighten the bobbin tension a little to keep the bobbin thread below the quilt surface (so I bought a special bobbin case and set the tension for FMQ and that's all I use it for.)

Lots of web sites that talk about how to free motion quilt. Then, it's PRACTICE, PRACTICE, PRACTICE! I use a portable white board and draw free motion designs on it (while watching TV, etc.). The idea is to get it fluid without jerking, jumping, speeding up or slowing down, etc. When your hand and brain are able to work smoothly, then you can probably do free motion quilting. Practice on scraps of fabric and batting (preferably the same kind you will be working on). Cut up some 14 inch squares of fabric and batting and draw designs on them and see if you can stitch them. Some advice: don't watch the needle...look at where you are going in front of the needle. Don't expect perfection to happen overnight. Many quilters have been FMQing for years and still make mistakes. (I've made a few quilts and my stuff still looks less than professional, but it's all mine!)

Free Motion Quilting with Janome 1600P sewing discussion topic...

All About Needles

According to the following web site, the feed dogs do not drop on this machine, Instead, there is a plate that covers the feed dogs:
Fluffy Sheep Quilting Do you have one of these Do you like it

Also thought this was interesting:
Oiling the PFAFF Grand Quilter 1200 Bernina Sewing Center Tampa

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The top thread breaks

1. the needle thread is not threaded properly

2. The needle thread tension is to tight

3. The needle is bent or blunt

4. The needle is incorrectly inserted

5. The needle thread & the bobbin thread are not set under the presser foot when starting to sew

6. the threads were not drawn to the rear after sewing

7. The thread is either to heavy or to fine for the needle

8. Try a different spool or cone of thread

try contacting Pfaff customer service for a manual

This should be an easy fix, something is wrong with the upper threading. Take the thread off the machine, raise the presser foot up and rethread the machine, that should take care of it.

this is a known issue with the pfaff.....i have just bought the machine and it has thread uptake issues...thread tension issues and it comes unthreaded by itself often...leaving globs of thread on the bottom stuck in the feed dogs and under the throat plate.....then the stitches are not properly balanced because the tension gets too loose on the bobbin thread....very disappointed to find out it is a known issue with all the viking husqvarna made machines...which are pfaff, janome and viking.....sux.

Might be that you need to lower the tensions quite a bit, you'll have to juggle with top and bottom tensions though, and experiment for just this operation with the Sensormatic.

Usually dirt in the tension plates. Pull a short piece of heavy thread through them holding the thread tight between both hands, work it back and forth to clear out lint.

My friend and I both have the Juki 98Q but on different frames - we were both having problems (needles breaking, thread getting tangled) we removed the thin metal thing inside the bobbin case and have had no problems since (over a year now!).

Q1.(A) Without realising, you could be 'helping' the material feed.
Q2. (A) Is the thread collecting at the start or during sewing?,,if at the start, make sure threads are clear and hold them out the back of work gently till a few stictches are made.
If during sewing, it could be tension isn't adjusted correctly, experiment.