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Old 2009-12-21, 08:56   #1
dans's Avatar
Oct 2002

3×7 Posts
Default Hard reboot

I updated my CPU & motherboard a while back to an I7 965 CPU w/an ASUS motherboard.

After upgrading I suffered from constant hard reboots (read: All good, blink, BIOS reboot screen).

After some troubleshooting I thought it was a cooling issue, so I installed a HUUUUUGE heat sink & fan combo with great silver-based paste (properly applied!) and the problem still persists.

Ah! Must be the power supply! So I went and bought a 900w high-end power supply, same problem... (sigh)

I can startup normally, but after 5-10 minutes my machine will hard reboot when running Prime95 v25.9 build 4

I don't see a spike in CPU temp, my system memory should be more than enough to handle the load... where am I going wrong? Bad CPU? Bad karma? I'd really like to get this system online and crunching bits.
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Old 2009-12-21, 11:47   #2
moebius's Avatar
Jul 2009

547 Posts

This very expensive but very good machine must necessarily be brought to run. For me (Phenom 955 BE), the same hard reboot happened after about 10 minutes - x hours if I set the multiplier to 18.5 x FSB / HTlink to 200 Mhz = 3700 Mhz. At 17.5 X 210 Mhz = 3675 Mhz, however it runs absolutely stable.

Last fiddled with by moebius on 2009-12-21 at 11:48
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Old 2009-12-22, 00:26   #3
Batalov's Avatar
Mar 2008

32×17×61 Posts

Try to find conditions where it doesn't crash. E.g. run it idle for a day -- will it crash?

Are you running Prime95 in crunching mode or in Stress Test?
Try different variants of the stress test: blend, small FFT size, etc. If in one of them it doesn't crash, you will get some hints.

Another idea: switch your preferences to trial factoring for a while. (make another folder, copy Prime95 and start it from there, for ease of restoring your work later) The point here is that TF doesn't use floating point susbsystem (or at least not as much) and will heat the CPU less at the same load.

If/when you will come to suspect your memory (or the memory controller) - try a different direction of testing: memtest, or something similar. Also, here, if you crashes are virus induced, you may find out that memtest (which is its own "OS") will never crash.

Just some ideas. Good luck with that thing - it is nice rig.
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Old 2009-12-22, 03:23   #4
bsquared's Avatar
Feb 2007

3,371 Posts

I had perhaps a similar problem with my workstation at work. At least, the symptoms were the same. Start anything CPU intensive and bang, black screen. Since it was a workstation there were 4 blinkenlights on the motherboard which diagnosed the problem as a bad voltage regulator. The IT guys swapped out the mobo and everything was fine. Maybe it's a wild goose chase but thought I'd contribute...
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Old 2009-12-24, 22:00   #5
PCZ's Avatar
Jun 2006
Chertsey Surrey UK

35810 Posts

This may help.

Drop the memory multiplier down.
2 of my i7's were doing as you describe when the memory was running at 1600mhz +
Dropped down to 1200 and the problem went away.

Memory throughput hardly changed at all, the i7 has more memory bandwith available than it can use anyway.

Last fiddled with by PCZ on 2009-12-24 at 22:02
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Old 2009-12-30, 08:22   #6
dans's Avatar
Oct 2002

3·7 Posts
Default Thanks for the leads!

I had a bit of time yesterday to fiddle with the settings all around.

Looks like a BIOS update to the motherboard resolved most of the problem, the system used to reboot within minutes of starting Prime95 (I'm running 4 large LL tests simultaneously) after the update I've only had one reboot in the past 30 hours... not perfect, but getting better.

I will reduce the memory multiplier next to see if that eliminates the reboots altogether, I have to wonder if the BIOS update didn't really affect anything other than resetting all of the BIOS defaults back to factory spec.

Thank you for the feedback, it has been quite helpful to aid troubleshooting this issue!

Last fiddled with by dans on 2009-12-30 at 08:24
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