There was a glitch in making the 6600 I found out through my dealer. He said always raise your feed dogs before shutting off the machine. Then turn machine on and wait just 30 sec or so then drop the feed dogs for FMQ. This information was given from the main manufacturer. I had my machine in for the same problem you had about 4 times and they finally really checked it out. Try it and see if it works for you. It did for me.