It appears that if one hashboard fails, the whole miner fails rather than just carry on hashing on the remaining (working) boards. I'm guessing this is something to do with the 3-phase power and needing the PSU to be balanced across the phases, however if anyone knows better please enlighten us.
As Phil said, odds are the Bitmain controller is not setup to run with 1 or more hash boards disabled.
he may be able to load braiins onto the controller if it is stock from bitmain.
braiins lets you disable boards.
As an aside I am playing with a 1 board setting for a t21. I will let it tune and see how it does.
I have loki chips which will allow for a totally non stock psu if I use the epic controller. I have a psu that says it will do 1500 watts using 120 volts and put out 13.8 volts with a 15% adjustment pot which means as much as 15.87 volts.
I am thinking the max I can do for a board is 60th and pull 1200 watts at 13.8 or 13.9 volts all within the specs of the psu.
Thus I am 90-95% sure a 120 volt 1 board t21 miner at 60th 1200 watts is doable.
It would be the most powerful 120 volt miner and one of the most efficient.