I will try to do my own investigation tomorrow, but C1 series had similar DC-DC and I think also with PIC. C1s DC-DC was very unreliable, some of them failed to set-up correct voltage and overvolted chips and shut down whole board. It is very strange as C1 DC-DC set-up voltage at 0.75V, but some voltage comands (after cgminer starts) result in wrong voltage setting. This happened over the time and some of blades can't set up even default 0.76V. Bitmain supplied "hot patch" by unsoldering buffer chip, so voltage stays at start-up level.
It is because of this sort of problem that I suspect that Bitmain have gone for a factory set fixed voltage. it is however possible that they have chosen a different set voltage for Batch 6 v Batch 8/9?
One thing that keeps alive the possibility of a dynamic voltage setting is that if they had just wanted a factory set Core Voltage they could just have used an EE based digital pot with no PIC?
However anything is possible right up to a programmed selection of voltage dependant on the frequency selected? Some tests and measurements will be good.
Rich
Bitmain's official response would support your idea of factory set fixed voltage:
Got the official response back on efficiency: "Currently, S7 is fixed with frequency to make sure the hash rate is more stable. but the voltage can be adjusted. The power consumption is 0.25 J/GH + 10% as marked in website."
So it appears the 4.7 is constant. And that efficiency is the +10 marked in specs.
It's been a bit since they sent that to me. But it did mention fixed frequency.
