The reason is clear. Lack of power supply. For frequencies above 750, it is necessary to increase the power supply to at least 0.9V with appropriate cooling of the chips and PWM drivers. At a frequency of 750, the chips work and do not fall off, but due to internal errors, the hashrate drops
I have batch 1 running on 750Mhz, are u suggesting that goign above has no sense as the hash will drop due to not enough power?
Absolutle so!. I also have several batch1 devices working in liquid. Temperature +45-48 degrees. They all can work at 775MHz - but hashrate become lower. After 750Mhz, voltage on hash chips dosn't change - 0.85v, and this voltage not enough for higher than 750Mhz freq.