I continue to find this extremely frustrating. I am running 6 S3+ units, each supplied by a 750-800W power supply with a single 12V rail and all four PCI-E connectors connected. I tried the 275/0815 settings, and exactly the same thing happened as the last time. Hour 1: fantastic, all units over 500 GH/s, holy crap why did I not do this earlier. Hour 2: OK, but hashrates down both as reported by units and at the pool. Hour 3: terrible, all hashrates reported by units and by pool way below stock results. So I have yet again reverted everything to 225/231/243/237/225/237 with voltage left blank.
I do not understand the mechanism here. If it is heat, why does it take 2 hours to show up? With the OC settings, all chips show up as "o" and working. But the hashrate results speak for themselves. But why the very prominent jump in hashrate for the first hour, but then utter crap out in hour 3? Can anybody explain this?
Just a few pointers that may help:
1. The voltage setting from the datasheet for the freq of 275 is both 0800 and 0850, so you can try anything within / around that range.
2. Hash rate falling in a few hours is NOT the "end of the day". Overall hash-rate is what matters in the long run (I usually let it run for 12 - 24hrs). If you are not getting X's on chips when the hash-rate is falling, I'd let it run as long as this did NOT coincide with a sustained increase in HW errors.
3. Do not be spooked by a fairly high HW error % at the start, and here I mean if the rate is less than or around 0.01 in the first few minutes to an hour, let it run.
S3 variants are the same but handle differently, so you may have to try different voltage settings (even freq settings). For example, the 262.5 freq does not ship from bitmain, but it turns out to be a sweet spot for most S3 variants!