You have bad chips on one board that are not opening or they are not getting enough power.

Run each board individually to see which board is chain 7 and see if it runs by its self. If it runs fine then you have a weak power supply or the lines in the wall have to much resistance to handle all three miners. I have seen several people with 16 or 32 amp circuits but the power lines them selves are to small. 

If the board does not run by its self try swapping the cable from the controller and see if it works, if it does then the controller is likely the issue. If it still does not work then ship that thing back to bitmain while you still have free shipping.