Damm, so much confusion sometimes and misreading who had what on mind often. I just read it out of curiosity and for virtual modder fun, at least for now. So I was not even week ago searching for service manuals for SM Or KM which I understand suppose to be basically in many regards twin motherboards and most importantly that same in the case of signaling and power delivery to MXM card. But I couldn't find full one only those without schematics. So I read today part of this discussion and was searching something about those motherboards and cards for them in the pursuit of understanding why new semi standard MXM RTX card do not work. Lo and behold I stumble into full service manual for X170SM with schematics! Look for the thetechstall page.
Unfortunately SuperMG is right: "PWR_SRC_NC". NC - not connected. Which explains that there is not much going on around PWR pins on the motherboard itself. At least that what I could conclude from crappy photos from web. So mystery seems to be explained. In my humble opinion it's not the end of the world. Next step would be someone to solder power bringing wires to those pins from PWR connector probably and trying those new RTX cards. It has to be done very carefully and precisely cos after those PWR pins are GND ones so we would not want short to happen there would we. But that's just technicalities ease to avoid. So what you think about this one?
