Tater wrote:
I'm trying to pin down a problem with my P8Z68 DELUXE/GEN3 system that
I built around two and a half years ago. The problem is that the
system will suddenly shut off and reboot, usually when the GPU is
pulling extra power (during gaming (Diablo 3), running Windows
Experience Index refresh, or when initiating a GPU stress test with
FurMark). The system will shut off completely (power light on case
goes off), and then will reboot by itself several seconds later.

I've run MemTest86+ and Prime95 extensively which would seem to rule
out the RAM and CPU. I have gone into the case and reseated all
cables, including the modular cable on the power supply. I've run
thorough OEM diagnostics on the SSD and HDDs. Power supply voltages in
BIOS look normal. I've even tried reverting to the previous NVIDIA
driver with no luck.

With the current GPU (MSI GTX 760), it will occasionally shut off when
I click the Burn-In Test button in FurMark. If it doesn't crash
initially, then it will run FurMark ok with the GTX 760. If I replace
the GTX 760 with the card I originally built the system with (an EVGA
GTX 580), it will shut off every time I attempt to run the Burn-In
Test in FurMark. Obviously the GTX 580 is a much more power hungry
card than the GTX 760, so it's looking like current draw has something
to do with the problem.

This was a totally stable system until just a couple weeks ago. When
I first put it together, the system ran 24/7 doing distributed
computer projects including CUDA, so the CPU and GPU (the GTX 580)
were running full power all the time, and I never had a problem with
that.

At this point I'm suspecting either the motherboard or the power
supply (Corsair CMPSU-850HX 850 watt Silver series) - the question is,
is there any way to further determine what the problem is without
throwing new parts at it? If I could narrow it down to the power
supply, that would be a lot easier fix than the motherboard.
Unfortunately I'd have to cannibalize another system in order to get
another power supply to test it with.

Systems specs:

MB: Asus P8Z68 DELUXE/GEN3
CPU: Intel I7-2700K
RAM: 4x4GB Corsair Vengeance low profile DDR3-1600
GPU: MSI GTX 760 or EVGA GTX 580
SSD: SanDisk Extreme Pro 480GB
HDDs: 2x1TB WD Black
PS: Corsair CMPSU-850HX
OS: Win 7 Home Premium SP1 64Bit

Thanks for any help and suggestions.

Jerry

With your symptoms set, I would tend to think power supply
at this point.

One thing I would check, is the green LED on the motherboard.
Asus motherboards usually have a green LED. The idea is,
when working on the computer, you don't pull DIMMs or cards
out of their slots, until the LED is off. The green LED
is tied to +5VSB from the power supply, and so it's an
easy way to monitor that voltage rail.

When your power supply shuts off, I would want to view
the green LED at the same time. It is wired to +5VSB, and
that voltage is part of the PS_ON# circuit as well. The
PS_ON# signal gets released, if for any reason +5VSB ever
drops out.

The power supply consists of two pieces. The motherboard
turns on the main section, using PS_ON# signal on the main
power supply cable. But the PS_ON# driver is powered by +5VSB,
and the supply shuts off, if the always-running +5VSB goes away.

+-------------------------------------------+
(PS_ON#) | |
v |
AC --- HVDC ---+--- Main_Supply --- LVDC 3.3V, 5V, 12V, -12V |
| |
+--- Standby_Supply --- +5VSB ---- RAM in standby |
---- WOL for NIC |
---- USB waking |
---- Helps with PS_ON# --+
---- (Green LED)

The +5VSB has a 2 to 3 amp rating (check PSU label for details).
Shorting +5VSB to ground, causes the chip on the motherboard
driving PS_ON# to get switched off, so then the Main_Supply goes
off. The green LED on the motherboard should not wink or
glitch - the switch on the back of the power supply, is
the only thing that should extinguish the Asus green LED.

Not all motherboards have that monitor LED. I think
every Asus motherboard I've owned, had that LED. And
it's great for observing the voltage that can lead
to the supply switching off.

A more likely cause, is the PSU is overheating, and
while the PSU has a current limiter, it's possible
it is thermal (heatsink inside PSU overheats, supply
goes off). If for any reason, the thermal sensor inside
the supply isn't working right, that could shut it off.

And your Asus motherboard will restart the system after
a +5VSB failure, if the BIOS is set that way. My systems
here, I set them to not Autostart. It could be that
yours is set to run the computer after a power failure,
and that's why it boots after the power failure. You
can adjust the BIOS, to have it sit in the OFF state,
if such a failure occurs. When you build up server
systems, you usually want it set to Autostart so all
your servers recover without you being present. For
desktops, it's the opposite.

Paul