Hi Ann. Did you ever get your XP-50 mainboard situation resolved…? I’m also looking for one myself. Bought an XP-50 “as is” … and when I opened it up, someone had already removed many of the caps from the board. But without the skill of a surgeon! A few of the cap pads are gone, and one of the white locking connectors for a ribbon cable is busted, and the moveable part missing. One of the contacts on the PCB board is uprooted as well. Seller says the previous owner did it - not him - and wished me luck. “Maybe you can sell it for parts”. That pretty much put this whole project on the back burner until I can get a decent mainboard. I’ve already gone and purchased replacement capacitors for it. Just need a nice mainboard that isn’t butchered.
Hi Mike!
No, I never got my beloved XP50 going again. I even had an experienced guy work on it. But to no avail. We’ve been looking for a working main board ever since. Again, also to no avail. 
(As difficult as winning the lottery?)
And such a worthy machine, too. 
~Ann
That’s a shame. Guess we just have to sit tight until something turns up. I did find some fellow in France selling one - but he will not ship to North America. Wasn’t a bad price either.
Yeah, sigh.
Keep the faith, eh?
And thanks for responding!