I sold a miner S9-13.5T running Awesome Miner firmware. It was tuned to run reliably at 15.6TH/s - and I had it mining at these settings for well over a year. It was configured with chain 5 at 743MHz/8.5V, chain 6 at 743MHz/8.6V and chain #7 at 725MHz/8.8V. Then individual chips were reduced in frequency from there until everything was in the "green" zone.  But this is causing my customer mining errors - seems like more chips were going into the yellow and red zones at his location. So he reduced it to like 700MHz across the board (not sure of voltage at the moment) and is trying to adjust from there. But, my question is why is this happening? My thoughts are that maybe his source voltage is less and/or Hz differences? At my location, I had constant 240-248V - pretty constant at 60Hz. So could this be the difference? He's ordering a Kill-A-What type meter now so he can monitor these things. But I can't think of why else he is having different results.