I have a s9 that has a failing hashing board. This s9 is an early 11.5th model, but I have a hashing board from a 13.5th unit to use as a replacement. I plan on learning how to flash a new os like brains to the controller. My question is will the os be able to handle the mixed batch boards?
There is really no way to tell unless you try, based on my experience most old S9 boards mix together well, this is specifically for S9/S9j/S9i, the newer models like the S9k is a whole different story, you can't mix different boards even from the same exact batch, there is SN on each hash board, the once I have are either labeled with an SN that starts with 1,2,3, so 1 will only work with 1 and so on, mind you that those were ordered and delivered on the same exact day, but for whatever stupid reason, Bitmain firmware won't allow me to run them on the same control board, so I ended up with a few miners that have a single hash board on them, which I can't mix.
Keep in mind that it's very unlikely that mixing boards will cause any damage, so you will lose nothing, you flash whatever firmware you want, and test it if it works - it works, if not - remove the incompatible hash board.
