Strange fan behavior [longish]

#21

On Wed, 25 Oct 2006 06:17:20 +1000, Franc Zabkar
<fzabkar (AT) iinternode (DOT) on.net> wrote:

Quote:

On Mon, 23 Oct 2006 10:37:47 -0400, George Macdonald
fammacd=!SPAM^nothanks (AT) tellurian (DOT) com> put finger to keyboard and
composed:

anyway I believe it's
established that the fan's built-in thermal control is supposed to track
intake air temp rather than heatsink.

Well, the following document suggests otherwise, although I can't see
how you could sense the processor's temperature unless the thermistor
were screwed down onto the heatsink.

Precisely. The CPU has an on-board thermal diode which can be read by
firmware/software to control fan speed; all the mbrds I've seen also have
an external CPU temp sensor which is read through the sensor chip. Both
can be read by SpeedFan.

Quote:

Cool ‘n’ Quiet™ Technology Installation Guide for AMD Athlon™ 64
Processor Based Systems:
http://www.amd.com/us-en/assets/cont...ion_Guide3.pdf

"All AMD Athlon 64 Processor-In-A-Box packages include thermally
controlled fans. A thermally controlled fan detects the current
temperature of the processor using a thermistor, and when a lower
temperature is detected the fan speed and noise is then reduced. Upon
detection of a higher temperature the fan speed is resumed at full
speed to appropriately cool the processor."

Here is one fan with an external thermistor:
http://www.nidec.com/designoptions/thermalfan.htm

Yep, looks like the one I already talked about with the "blue blob" and two
legs but obviously that's not going to control fan speed based on CPU temp.

--
Rgds, George Macdonald

#22

On Wed, 25 Oct 2006 15:31:49 -0500, Ed <nospam (AT) hotmail (DOT) com> wrote:

Quote:

On Wed, 25 Oct 2006 06:17:20 +1000, Franc Zabkar
fzabkar (AT) iinternode (DOT) on.net> wrote:

"All AMD Athlon 64 Processor-In-A-Box packages include thermally
controlled fans. A thermally controlled fan detects the current
temperature of the processor using a thermistor ....

Sounds to me like AMD is trying to make it sound better then it is.

The document is >2 years old.

Quote:

The thermistor isn't anywhere near the CPU or even touching the
heatsink, so how's it going to adjust the fan speed for CPU temp?

If the fan is at it's minimum of 3K RPM and you put a full load on the
CPU and the CPU die temp jumps from say 30C to 50C the fan will still be
spinning at 3k, it'll only spin faster when the temp of the air passing
through the fan warms up. End of story.

Exactly! The fan-mounted thermistor is simply to give a higher airflow
when the ambient temp, i.e. inside the case, is higher.

--
Rgds, George Macdonald

#23

On Wed, 25 Oct 2006 15:31:49 -0500, Ed <nospam (AT) hotmail (DOT) com> put finger
to keyboard and composed:

Quote:

On Wed, 25 Oct 2006 06:17:20 +1000, Franc Zabkar
fzabkar (AT) iinternode (DOT) on.net> wrote:

"All AMD Athlon 64 Processor-In-A-Box packages include thermally
controlled fans. A thermally controlled fan detects the current
temperature of the processor using a thermistor ....

Sounds to me like AMD is trying to make it sound better then it is.

The thermistor isn't anywhere near the CPU or even touching the
heatsink, so how's it going to adjust the fan speed for CPU temp?

If the fan is at it's minimum of 3K RPM and you put a full load on the
CPU and the CPU die temp jumps from say 30C to 50C the fan will still be
spinning at 3k, it'll only spin faster when the temp of the air passing
through the fan warms up. End of story.

Cheers,
Ed

What you're saying makes a lot of sense. In fact AMD's own docs appear
to contradict themselves in this regard. One refers to airflow
temperature, another to processor temperature. <shrug>

Anyway I've posted a related question to alt.comp.hardware.homebuilt:

http://groups.google.com/group/alt.c...2cb577 1cc8a1
http://tinyurl.com/yhuzhd (short)

One person states that "on a prior Asus board (A7N8X) with ITE IT8708
Super I/O, just before the fan header there's a 100uF cap, then an
HJ772 (PNP transistor) that looks driven by an LM358".

I suspect that the OP's motherboard probably uses a similar design, in
which case it would be DC rather than PWM. The question as to why a
fan speeds up when its voltage decreases remained unresolved, though.
I still think my own explanation is plausible, in which case the OP
would be advised not to run his fan at any voltage other than 100%. I
mean, why would you want to control a fan that is designed to control
itself?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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Strange fan behavior [longish]

Hardware Chips Processor, cache, memory chips, etc. (comp.sys.ibm.pc.hardware.chips)

Re: Strange fan behavior [longish] - 10-24-2006 , 06:50 PM

Re: Strange fan behavior [longish] - 10-25-2006 , 11:58 PM

Re: Strange fan behavior [longish] - 10-26-2006 , 04:51 PM