Does PWM stop CPU fan if CPU temp is low?

2739 Views 7 Replies 6 Participants Last post by rkirkw, Mar 11, 2009

rkirkw

Discussion Starter · Mar 6, 2009

I just put this system together last night and was verifying if everything was working before loading an OS or overclocking.

I have a Xigmatek HDT-S1283 with stock fan on an AMD Phenom II 940 on a Gigabyte AM2+ MA790GP-UD4H board.

If I connect the fan directly to power, it spins with no issues.
If I connect it to the 4 pin CPU fan connector on the motherboard, it does not spin, but it pulses forward randomly like it is just checking to make sure it is still there.

The board has PWM fan control enabled.
The processor has only reached 19 degrees celsius even without the fan running. Ambient temp is 20 C.

Is is possible that the motherboard is simply not calling for the fan to spin because the processor is not hot enough to require additional cooling?
Do you think I could have a defective fan or motherboard?

Thanks!

Kirk

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BikePilot

· #2 · Mar 6, 2009

The mobo can usually control the fan speed. There's an option in the bios for that, check it out.

I'd worry about that reported temp, the PhII is a pretty hot chip so chances that its really running 1 deg about amb are pretty minimal.

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Liability

· #3 · Mar 6, 2009

The fan won't kick on until a certain point. Go run prime95 or something to make sure.

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laxrunner

· #4 · Mar 6, 2009

Quote:

Originally Posted by rkirkw

The processor has only reached 19 degrees celsius even without the fan running. Ambient temp is 20 C.

Wait, the cpu has only reached 19C and ambient is 20C? Um...something is wrong. Think about that one, there is no way the chip is cooler than ambient on air cooling. Physical impossibility. I don't know what to tell you other than that but I would be very careful about loading it without the fan running. Maybe force the fan to run and stress it to see if the cpu temps go up, otherwise you may have bad thermal diode in the chip.

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huntman21014

· #5 · Mar 6, 2009

My cooler would do that and I would have to manually spin it to get it going, the problem went away when I disabled the PWM function

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rkirkw

Discussion Starter · #6 · Mar 9, 2009

Thanks for all the replies.

I do think there may be an issue with my CPU temp probe - it seems to read about 5 or 6 degrees cooler than actual.
I went back through my settings and found that somehow the CPU Fan speed control had set back to Auto. Changed it once again to PWM and the fan spins right up - so far to 833 RPM.

Since I am still testing, the case is still open. I have an indoor/outdoor thermometer and put the outdoor temp probe on the exhaust side of the Xigmatek 1283. Even running 3DMark06 and Orthos on 2 cores I never saw the temp on the thermometer get above 28 C. There is a 140mm fan 1.5 inches above the CPU Cooler in the top of the case and another 120mm at the back of the case not too far away either.

I need to find a version of Prime or Orthos to work all 4 cores so I can generate some heat.

Kirk

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nigel

· #7 · Mar 9, 2009

i remember my old motherboard and cpu fan.
that thing went up in gears 1 to 6 lol when it hit 6th gear it was unbearable it sounded like the comp was going to take of

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rkirkw

Discussion Starter · #8 · Mar 11, 2009

I think the BIOS is simply reporting the CPU Temp wrong - hopefully a BIOS Update will fix it.

I overclocked to 3200 and installed SpeedFan. I then ran 3DMark Vantage and saw the CPU temp there get up to 48 C with ambient at 23 C.

I saw mention somewhere that the Deneb core temp sensor was reporting differently than previous Phenom chips. Gigabyte apparently needs to determine which chip is installed and adjust it's reporting accordingly.

Kirk

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