I guess the motherboard is the main board that makes the machine run. The serviceperson said there are several other boards in the machine, but this is the most important one. I have the machine back and it is running great. Keeping my fingers crossed.
A couple people mentioned a dealer in Howell, Michigan. We live in the Upper Peninsula of Michigan now, but our family is in Jackson not far from Howell. If I have a problem againg it would be a good excuse to go back and visit family and take my machine there.