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Thread: CPU throttles down on Prime 95

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    CPU throttles down on Prime 95

    Hi all,

    I've just performed an overclock of my Phenom 9550 from 2.6 to 3.2ghz at 1.4V. It's nice and stable, although I've still got to do a 24hour prime 95 run, and stays at 40-42degrees C at full load.

    The only concern is that when testing under prime 95 I get occasions when the CPU throttles itself down to 1.3Ghz, causing a huge temperature drop. When I first saw this I was using the stock cooler and I thought it was the CPU putting in the auto throttle to save itself from burning out - it happened around 53ºC which is a little hot. But having replaced the cooler with a nice big Zalman and having knocked 10ºC off the 100% load temp I'm still seeing this - 42ºC seems an awfully low temp to be throttling back due to heat...

    I also thought it might be down to Cool'n'Quiet, so I disabled this, but no change.

    What gives guys? Is my machine telling me I need to scale back my overclock? With the low temps under prime95 I was hoping to go even further.
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    Re: CPU throttles down on Prime 95

    The original Phenoms weren't that great for OC-ing anyway but i don't know why Prime95 would throttle down your clockspeed if CnQ is turned off - it does suggest a heating issue but if you've got a propper cooler then im lost tbh :S Maybe check the heatsink again ? I think CnQ wouldn't affect Prime runs anyway as it only comes into effect when idlign doesn't it ?
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    Re: CPU throttles down on Prime 95

    Yeah, that's my understanding of things.

    I'm giving it a more realistic test now - exporting a bunch of RAWs into JPGs from lightroom, and it's got the same behaviour. Temp is mid-30s at idle, it builds to 44ºC and then gets throttled to 1.3ghz. I'm fine with the idea of CPU throttling - I really don't want a fried CPU, but throttling at 44ºC when before in my old case and with the stock HS/F it used to idle around that? Is it possible that it's actually going hotter than 44 but that speedfan just isn't logging it?

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    Re: CPU throttles down on Prime 95

    Can I give this one a top? Here's a couple of screenshots while running Prime95:

    Machine starts off good:



    and throttles down at 45ºC:



    I've got a Corsair 550W PSU, I've disabled Coolnquiet, I've turned windows' cpu management to run it at 100% all the time... Motherboard incompatibility?

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    Re: CPU throttles down on Prime 95

    If you're using Vista check energy saving settings to make sure its not throttling the CPU.

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    Re: CPU throttles down on Prime 95

    Win 7 - and I have done, max and min frequency settings are both at 100%.

    Even so, neither that nor Coolnquiet should have any effect because the throttling is taking place under 100% load. I've used Coolnquiet and it works very well, throttling up and down as required - but I don't want my CPU throttling down half way through something. It's got to be some hardware monitor somewhere that's decided that 45ºC is the cutoff for that CPU - but where?

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    Re: CPU throttles down on Prime 95

    Not really helpful but is there a bios setting somewhere; I know you can get it to sound an alarm. Maybe just clutching at straws.

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    Re: CPU throttles down on Prime 95

    Been through the BIOS - I've disabled Cool'n'quiet and temperature monitoring.

    I guess what I should do now is reset the machine to stock and see if I still get this. I've never seen anything like this before, but I guess it could just be my machine's way of telling me that my hardware can't handle that overclock? But if it does it at 2.6Ghz I guess I'm looking at replacing some part...

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    Re: CPU throttles down on Prime 95

    Ahha - might have found something.

    Apparantly there are 2 versions of the 9950 - a 140W and a 125W version. It looks like my Asus M4N78 can only support 125W CPUs... Would this explain why it throttles at full load - the mobo being unable to give it enough juice at full power? The only problem with my theory is that I'm not 100% sure which version I've got - I don't have access to the box right now. Can anyone give me a firm identification? This site here:

    http://www.techwarelabs.com/re...enom-9950/index.shtml

    claims that their Phenom 9950 is the DR-B3 revision and is a 140W piece - does that ring true for mine as well? I've posted CPU-z screenshots above.

    Thanks for your help, and hopefully you can confirm that this is the source of the problem! If so I'll have no problems returning it for a replacement - I've got a good relationship with my local shop

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    Re: CPU throttles down on Prime 95

    What's happening with your voltages at the same time (speedfan should show these too)?

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    Re: CPU throttles down on Prime 95

    M4N78

    M4N78 PRO

    Not sure if this helps, the pro/ non pro bit is written under the PCIe port. non-pro = 125W

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    Re: CPU throttles down on Prime 95

    Yeah, I'm happy with my Mobo, it's definately the non-pro version.

    Still looking for an ID for the CPU in software using the CPU-Z results. I don't have the box with me atm, and if I don't want to remove the HS/F - it involves taking the mobo out of the case and I'm all out of thermal grease...

    I take it running a 140W chip on a 125W tops mobo is a bad idea? Should I keep the machine shut off until I get this sorted?

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    Re: CPU throttles down on Prime 95

    Oh well - a resolution. Gave AMD a call and they were great - they said faulty CPU, just said ship it in for replacement. Wasn't going to be using it much over Xmas anyway, so I think I'll do just that. Not quite sure I believe that's the problem, but it's a simple resolution

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    Re: CPU throttles down on Prime 95

    If it like GFX card RMAs maybe they will send you something newer like a 140W 965!

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