Why there are so many heatsinks on the testboard?
Why does the GN chip gets to 76 C degree, even when it is underclocked?
Why does the GN chip gets so hot, even with watercooling?
im not in any way related to hashfast (am just a customer) but here's some thoughts...
a test board & box may well be different from a production box. they probably have to have extra capacity of power & cooling in there so they can run it at beyond its normal limits and see how it performs... so to assume that the production boxes will have to be the same isn't necessarily so.
i really don't think if it runs at 76 degrees at 424 gh that this is technically 'underclocked'. and anyway, i think the word underclock may have been misused. generally underclocking would also require under volting (to reduce power consumption). so its possible they mean that its running at under nominal voltage.
at 76 degrees, there isn't much more room for over clocking. I'm presuming that most engineers don't want to see their chips to get much hotter than 90-100 degrees in extreme overclocking, and at 76 there isn't a lot of margin to play with. it really cant get much hotter than 76 and be run for long-term reliable sustained use.
presumably they are playing with different voltages, and clock speeds as we speak.. to see what makes the most sense for long-term use.
the documentation hashfast put out showed that when running at nominal volts and clocks it should run at 424 gh/s... so to then call that 'underclocked' is odd as that was the intended gh rate (according to their docs)... so yes, it does seem likely it can run faster than the nominal clock.. as most things can. 5-10% should be easy. And the 20% they were gunning for, with some extra volts, should well be possible.
the earlier claims of it running at 500 gh may have also been true, but they also specified that with half the cores running it was consuming 300 watts.. which is clearly too high and if the other two cores also consumed 300 watts, the total of 600 watts would be much too much for that package and cooling system to cope with. This may have been putting a strain on the rest of the system and it may well be that to run at 500 gh (or more) for a sustained period will require everything else in the system to be behaving itself very well (power, airflow, dc/dc converters, cooling etc).
its not difficult to overclock something for a few minutes... but try and run it overclocked for hours or days and the rest of the system needs to be able to cope. fingers crossed, it can as I'm really hoping my hashfast gear will clock at 500+ ! but i will still be happy if it runs at 424 gh!