Sold miner to a buyer but it's not performing the same what's up with that?

I sold an S9-13.5T miner with Awesome Miner firmware. It was set up to run steadily at 15.6TH/s, and I had it mining like that for over a year. I had chain 5 at 743MHz/8.5V, chain 6 at 743MHz/8.6V, and chain 7 at 725MHz/8.8V. Then I adjusted the individual chips' frequencies until everything was in the "green" zone. Now my buyer is running into mining errors. It seems like more chips are hitting the yellow and red zones at his place. He's dropped the settings down to about 700MHz all around (not sure about the voltage right now) and is trying to tweak it from there. So I'm wondering why this is happening. I’m thinking maybe his voltage supply is lower or there are frequency differences? I had a steady 240-248V and 60Hz at my location. Could that be the reason? He's getting a Kill-A-Watt type meter to check on this stuff. I just can’t figure out what else might be causing these different outcomes.

Most likely the miner is running in a different temperature environment. The PSU does not care about 50/60Hz though too low of a line voltage of could be an issue.

yeah if he is 225 volts and you are 244 volts the psu will work better. i wonder if it sags to 11.5 dc but room temp and air flow matters so it could be a warmer space and lower voltage issue combined. good luck.

Thanks guys - temp could be a factor - I ran these in the mid 50's (F) so nice and cool for them. My customer is running in an apartment - so probably 70 or something. So maybe a heat issue. Nothing to do about that other than back it down a bit unless he wants to cool it better. Hopefully he'll get a voltage for his main power so we can see if that may be a factor too.

S9 boards regulate internally. It's very unlikely input voltage is a factor. But given you're asking a machine that's already not the best design for cooling to run a 15% overclock it's far more likely a heat issue. The ASICs will actually draw more power as they get hot, which makes them hotter, which draws more power, and because of the string topology they all run in a sort of easily-perturbed power balance, so when overclocking, temperatures become a big factor for stability. A 10C increase in input air could make a big difference.

Why isn't he just letting it auto-tune? My experience with AM firmware (and all the derivatives of the main source of it) on an S9 is that auto-tune can do a decent job and then some hand tweaking after that can be done. But what I have seen is that after auto-tune and hand tweak, it'll show great for many hours / days and then things will turn downhill. For what reason I'm not sure but I did have to go back in and do some more hand tuning.  Just for comparison my 2 S9's  are running an average clock of around 713Mhz avg., 8.4x volts for 15.25 TH/S but that is with asicseer firmware, 1250-1300 watts, 240vac, ambient ambient 60 F, S9 temp. at 70 C with fans at 2400rpm.