I had a long talk with my sewing tach about my D1 a few years back. He said at the time, that they used to be able to locate "used" motherboards but no longer could find them, then for a while, they could refurbish them if they could find one that this could be done to. Then sadly, they could not even do that. One person had brought her D1 in and it still could do a very nice straight stitch but apparently nothing else. So she just took it back home. Sadly, my screen went blank so I bought myself a new Topaz 40 which the tech said could pretty much do what the D1 could do plus a few more things. My D1, being an older machine felt a bit more solid to me, but the Topaz 40 does an OK job.
If you can find a Pfaff tech, that is where I would start.