Virginia-- (and Janet)--Did you mean to say that prewound bobbins that are NOT Janome brand.....can cause the problems that Janet is having?

   I feel Janet's pain. I have had a similar problem, but with my MC500e machine. My bobbin would jump all over the place and make a terrible racket. I took it to the dealer and it would work for a short time, then the same thing would return---jumping bobbin, bird nests,etc. I was at the end of my patience with the dealer and Janome in general. However, the last time I took it in, the store owner sat my machine next to their floor model and compared the two machines, piece by piece. It turned out that my machine was actually lacking some obscure part which I believe is called the bobbin stop or stopper. He took the piece off of their floor model and put it on my machine and it has been good ever since. I assume they ordered a new piece for their floor model.  With an abundance of caution, I replaced all of my bobbins with Jenuine Janome brand, the ones with the rubber additive in the plastic that makes them more stable. I even ordered some pink ones, reserving those exclusively for my embroidery machine. The others are for my Janome Skyline 7, which is sew-only, no embroidery. I also bought a spool of Janome brand bobbin thread. Personally, I thought that thread looked a bit "linty" but it did a good job. I also have used Bottom Line bobbin thread with great success in these new Janome brand bobbins. I like to have LOTS of bobbins, so I ordered a bag of 25 of them for a very economical price from a place that has the word "Pocono" in its name. Pocono Sewing Supplies or something like that. I am not sure where I bought the Janome bobbin thread, maybe at the same place as the bobbins.  The genuine Janome bobbins have a "J" stamped into the core of each bobbin. You can tell if they are the newer, rubberized ones by tapping one on a front tooth (!!)---the non-rubberized ones make a sharper, crisper sound, the rubberized ones make a sound that is a bit duller and "softer". There is also a slightly different "feel" in your fingers between the two bobbin types. HArd to explain that one, but you will be able to discern the two.  My experience has been that once that "stopper" thing was installed and the changeover to the genuine, rubberized bobbins, I have had smooth sailing. I hope this solves your headache. 

If it does not, then yes, I would persue something with Janome--if neither their dealer nor the repair depot mechanics can fix it, they should replace your "lemon" of a machine.Three years is too short of a life span  for a machine that costs thousands of dollars, especially if it has spent months just in transit to and from the service depot. 

Good luck to you and let the Group know how this turns out for you.

Kathy Strabel   Camas WA   USA