I have a Pfaff 7550 that started to have "that presser foot going down very slowly" problem. I did some research and found that the spring in the column that works that presser foot gizmo had become less springy (pardon all the technical jargon). Eventually I couldn't even get the presser foot to stay pressed down on the fabric/feed dogs in order to sew. Took it apart partially but realized that yea, it is computerized and I didn't want to ruin the machine because I got it for a fantastic price and more importantly, I love it! So off to the dealer to get it replaced. Runs like a top now. Oh I hope that machine cannot read because as soon as I say something like that, you know what will happen.
I do have a battery in my machine but I think it is only to keep stitches that I have saved in the memory but I might be wrong on that. I too would think that if the mother board is toast, it would not work at all. Hope you can figure out what the problem is. Probably taking it to the repair guy is a good idea. Might need a good healthy cleaning and tweaking to get it up too its highest potential