question & problem's basically in the title
for starters, the background:
setup:
got a maximus VIII Hero (the regular NOT the alpha) at a below bargain price from a friend who don't need it no more. Bios is latest version
I had several sky & kaby lake CPUs which I got at a good deal so I tried them on the mainboard: three i5-7500 , one i5-6600K and one i7-6700K (I might keep that last one. sold the others for a profit)
using a 4gb Crucial stick for ram. the ram's reference is in the board's QVL
before I start: all those CPU's, the ram & the mainboard are stable under stress: Prime95 OK, Memtest86 also OK
I assume prime95 (especially test #2) is also a good way to test a mainboard right?
for testing I use a windows 8.1 liveCD on usb
and now, the symptoms:
whenever C-states are enabled in bios (specifically: C-states enabled AND at least 'enhanced C-states' enabled) then whenever I'm about to enter windows (basically it's on the login page with the avatar icon & the spinning dot-circle): the system suddenly reboots (as if I hit the reset button)
C-states are important cause they're the only way of lowering cpu voltage on idle so I'd like to be able to use them
I tried fiddling with other bios options (with C-states) enabled: no luck, I have to disable C-states to be able to boot into windows.
the only exception was with the i5-7500 cpu's (all 3 of them) where I could enable C-states BUT then I had to either increase "ram current capability" to at least 120% (that's of course not a viable option) or disable anti-surge protection (not a viable option either)
so apparently: this board is fully incompatible with C-states if skylake cpu is used, and *partially* incompatible with C-states if kabylake cpu is used. crazy huh?
so why the sudden restarts? why are the Maximus VIII boards (or does it only affect the Hero? dunno) incompatible with C-states? (as my experience proves)
>>> and before anyone asks: the PSU is a VERY HIGH END one bought in 2010 but easily as good as today's best: the Corsair VX550 (not to be confused with low-quality VS & CX series)
it has ALL-JAPANESE capacitors (that alone proves the PSU can't be the cause of problems) great ripple-suppression & very tight voltage regulation (as reviews have shown)
in other words the PSU is not to blame for this (I say this cause I don't have another PSU to test with, but as I've shown the PSU can't possibly be the cause)
so the problem definitely comes from the mainboard