Hello i have a similar problem
I recently bougth a Antminer S7 Batch #8 this miner have been instaled just a few days ago and i have serious troubles operating it.
When i recived it, the hash rate success the 4700 GH/s but latter that day it dropped to 3900 GH/s, this is almost 1000 GH/s below the indicated. Then i move the miner to another location there the hash rate was even lower around 2900 GH/s. In view of this i decided return it to the firts location where it was and i reset to default the antminer in the panel of control but my problem was scalating and now the miner is working below 1300 GH/s.
I have noticed in the miner status the temperature of the hash boards 1 and 3 es really low, below of the 40 degrees each (img1 attached). Also attach images of the miner instaled
I have tried to change the PSU unit and the cables of the PSU but nothing seems to work.
I would appreciate any help or guidance you can provide me to solve my problems.