Still waiting on two more batch 1 orders dated 9/04 and 9/15.
Also have a pre 8/31 unit which stopped hashing at optimum (dropped by 1/3) after 10 days online. Hard and and soft reboots with not change. Appreciate some assistance on warranty service, Bitmain. Reference your support ticket #4143.
Do you know which board? Sounds like a board if it is one third. You can see a little red light on the hashboard near the connectors.
If no red light then...
You can detach hash cables one at a time to find the offending board.
Sometimes dropping the frequency will pop it up.
Have one s7, lots of time with other bitmain products.