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I don't know exact history. The customer is kind of a weird guy who is really hard to have a conversation with. A man of few words.
It has been in an AASP where they just offered him to replace the MLB. I can not see any corrosion anywhere but when I looked on the board under the microscope I could see small brush marks as if someone tried to clean something off between the ram chips. I gave it a UC but still the same. I suspect it had a minor liquid damage at some point and I will see if I can get the customer to admit it.
the SSD controller gets a little hot (~50 C) when connected but is not recognized. When I take the SSD out and into another machine it is working fine and do not get as hot.
Yes. Several times. Same issue. Tried with several different SSDs (from different models and years) including PRAM reset every time I switched SSD. Just blinking folder. All the SSDs I tried works fine in another computer. And the SSD that came with this machine works fine in both another Retina and Air.
3V bus can supply enough current into a 10 Ohm load. A rail will never be low because then there would be no "PGOOD" signal and the whole machine would be dead. A power rail is not some "no current" logic signal that can be anything between high and low.
I guess the dead U3900 was messing with the PCI_E bus.
Thanks for the explanation. It makes sense now. Mark solved and Merry Christmas
Oh. And just one more question. You mentioned in the first post that this not just happened by itself. Was it for sure some liquid (even though I did not find signs that could tell 100%) or can this chip fuck up by itself after all ?