I doubt one is available. It is not needed for field service by warranty stations or even national distributors since nothing is repaired at the component level. Board level is the closest they get to the details of the circuit. That is pretty normal for electronics now. It is cheaper to stock boards, with their high resale value, and saves a great deal of time to replace a $300 board when a $0.01 SMD cap shorts. When my SB900 quit, still under warranty, I did not want to incur the $300-400 round trip shipping fee so got into it and found that a chip bypass cap shorted. Replaced it and it has been working great for 3 years. Total cost of parts....I got robbed, the store wanted 2 rubles, or $0.06, 6 times its value. But much better than the $200-500 entire circuit boards replaced with not more expensive of a part fails in your car or camera body. I collect service manuals for the older cameras when I can find them. I have about 12 in PDF format but the newest one is the D90. Stan St Petersburg Russia
Stan - Obviously you have the depth of understanding to even identify the problem and its cause. Today we see less and less of that. It's easier to train repair people to consult a list of FAQs and replace an entire board than it is to teach them how to diagnose a problem and fix it at the component level. When's the last time most of us raised the hood of our car and recognized much of anything? Not only can we not sit on the fender with our legs dangling in the engine compartment anymore. We can't even see the ground any more!
Oh, I misunderstood that you wanted a drawing of the internals or exploded view. Schematic has a different meaning for electronics types like me. The service manuals of the older models have a lot of illustrations with every part of the mechanical assembly shown. I think you will have to wait a bit longer before service manuals for the D800 get posted on the internet. Stan St Petersburg Russia