What settings you have in the BIOS for tha SATA controller ? Which mode it is AHCI or IDE this is also important, If you don't see it, change the mode to IDE.
I asked this so many times but i never got an answer.
I've wokred with people that really want help but do nothing to actually get a proper help.
If you are talking about a 3.5M$ you have to provide a proper information so we can somehow remotly find a solution.
I have no crystal ball to tell from a probably few thousends kilometers what's wrong with frankenstein's type of a harddisk, repaired by god knows who. This is not the way.
There should be a simple system. You collect and provide all the possible data(info) so you can apply the most efficent solution, otherwise you are just gambling with 70 bitcoins... and the odds are against you.
Sorry OP but I really get upset when people do not understand the situation they put the others that are trying to help. You need to at least answer the question we put here, if you cannot answer, please ask so we can explain in details what you need to do in order to answer them. That's all.
This usually happens when one of the chips get bricked or the device does not pass one of the power on tests it runs when first turned on.
I had hoped it was a faulty temperature sensor that will send a false reading to the controller which will then go into emergency mode because it thinks that the hardware is overheated.
This is a common issue with these type of devices, and these issues will have the exact same outcome: controller visible but no IO possible.
I am still convinced that this is most likely the issue so my last advice was to check the storage hardware chip by chip to see if/which one went rogue but of course to do that will take more tools and equipment so that's where we came to a stop.
I am also still convinced that the data needed to recover the coins could still be there on the device, but i do not think that it is going to be easy to get access to it, simply because we tried all the easy things and unfortunately those appeared not to work.
So you dug deeply into solving possible hardware problems.
First I would check the 3.3V and 1V that comes from the power regulator to the controller. There's also a 3.3V going from the regulatior to the NANDs, only to exclude the physical damage from the so called "repairs". The drive could be OK before the repair, you never know what they did, so basically check everything.