I spoke to the owner of the repair shop yesterday and it was the Main Board Processor board that died on my Nikon D810. The good news is that he already has the part and I should have my working D810 back in my hands today.
My D810 is out of warranty so I saved myself a lot of time by taking it to a local repair shop instead of sending it to Nikon. Of course the repair would have taken longer if the part had needed to be ordered from Nikon.
The timing on this repair has actually been good because the weather turned back to winter or “sprinter” (spring+winter) and there have been gray skies, snow, graupel and rain in the valley that would have prevented me from going shooting anyway. It is snowing lightly as I type. So I haven’t missed any actual time in the field.
I wanted to post an image with my D810 update instead of having a white page with just text. This photo of a Red Rock Lakes NWR sunrise is one that that I created on the last day of my last trip to Montana last year. When I look at this image I am reminded that life is good.