I have a similar problem with S5.I have sent a board to Bitmain.They will check.I have never over clocked.
I have measured the voltage of working and not working board.I have found the problematic chip by this way.If a chip is malfunctioning the board does not work.
I recommend you to measure the voltage of first and last chips.
Today, I can not access to the miner.I am suspicious of a virus which effects miners.
Oh, damn he said he is going to smash them if they do not sell On Ebay,lol. Hes NUTZ! Has them both for $50 w/ $19 shipping, w/ the wrong pic,lmfao!