I bought a new 6600 and had to replace the foot pedal. I noticed the machine was slowing down, and it eventually stopped. I'd heard others on the Janome forum talk about having to replace the foot pedals. At least it was still under warranty, so I didn't have to pay for the new pedal. I also had a problem with the tension knob slipping all the time. I actually taped it in place to keep it from moving. I took it in and they tightened the knob. It's still a little loose, but it doesn't just slip on it's own. I would set it on 4, and the next thing I knew it had gone down to 0 all by itself. I don't know if your problem is the pedal, but you need to take your machine in and have them look at it.