OK Braiin OS installed to NAND. ( Using 16GB card, with 8GB there was an error "firmware.tar.gz" is missing )
Seems that the missing hashboard appeared and hashing.
However in Braiin OS there is no temperature measurement!
...
Braiin OS seems very powerful firmware but missing temperatures sensors is very dangerous.
So i tried to install 201711171757 bitmain firmware from official page with no luck
Well you can also manually control the fan speeds. If you know it never got to dangerous temperatures with factory, it won't with Braiins OS unless you overclock it. It seems to be unable to detect the sensors but that's not so strange as you may think. It would be fine if you could get temperatures from one of the boards, then put that in the middle (which is the worst position).
You can try factory from 2017 and 2018 if you think it makes a difference. But yes, factory loves to disable a board when it can't read its sensors, something bOS can override as you did see. Sensors failing but hash chips actually ok is not rare.
If you are somehow still scared with bOS go the other route: Downclock. Something resembling 8.1v 500mhz does wonders. You could try 8.5v 600mhz or so, just make sure actual and ideal clock speed match or are very close, then keep lowering that voltage and when the values differ too much go back to the previous value. Downclocking is never dangerous, chips run cooler. And don't mind the suggested values, lower those voltages always until you find the sweet spot.
I mean a downclocked board is better than no board, but its your choice...