I have the same problem with my Viking Sapphire 870 Quilt. Have a day (about 6 hours) of sewing the feed dogs stop working. Usually waiting overnight clears up the problem, but this time it's been 3 days. I've had it to two shops about 4 times and they can never find anything wrong. I am ready to trade it in for another machine. And since my best sewing shop is also the repair shop, I'll probably get a newer Viking, too.