CPU throttles down on Prime 95

[brammers]

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.

[Terbinator]

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 ?

[brammers]

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?

[brammers]

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?

[mrt9888]

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

[brammers]

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?

[Domestic_Ginger]

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.

[brammers]

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...

[brammers]

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

[kalniel]

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

[Domestic_Ginger]

M4N78

M4N78 PRO

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

[brammers]

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?

[brammers]

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

[Domestic_Ginger]

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