Maybe I wasn't clear. I have a
working 841 left that it is hashing.This means that the PMU and the MM board works at the working one. I have putted the 12 hashboards of the 3 broken 841 in batches of two(hashboard #0 and hashboard #1) to the working one,leaving hashboard #2 and hashboard #3 in the working 841, and I get ECHU ( 131073 131073 0 0) which means the #0 and #1 hashboard doesnt work. And the unit hashing at around 7 Th/s.
(Will upload log as soon as I go to the farm).
Maybe the MM board is broken? Can you try with a surely working MM board?
How does the pmu voltage measurement values look like in the cgminer api log?
Can you post the log here? (please insert it inside code tags, it's the #-button in the message panel.)