Very Nice shots. This makes a lot of sense, however still does not explain why they have used a PIC as opposed to a non volatile digital pot and no PIC? Unless.... under different circumstances on a given board the PIC writes a different value to the Pot?
You're right, and I should more properly have said, "Looks like the digipot may be used for voltage binning of the the hashboards, plus other unknown applications"
I've only looked at startup behavior so far -- no idea if there's any runtime behavior from the controller or the PIC (can the controller even talk to the PIC? I haven't investigated that at all). OP indicated that the PIC actively tries to adjust voltage on one of his modified boards:
I belive that PIC is able to decrease voltage right after start-up of chips, one of my board is only 9.5V which PIC always adjust (tries to override my pot settings) after chips start. Simple mod can't easily check when chips starts.
So it may not be coincidence that the new value is written right as the voltage ramp finishes.
Anyway, I'll keep poking at this in spare half-hours.