alas, you still ignored my previous post and failed to post the kernel log in the code tag.

Anyway, do the following

1- Disconnect hashboard 1 and 2 and let the miner run with just board 3.

If it doesn't start hashing

2- Disconnect hashboard 1,3 and leave only hashboard 2.

if it doesn't work

3- Disconnect hashboard 2,3 and leave only hashboard 1.

by performing the test you will get a few answers which we can discuss later on.