"Ken" said:
I am on my second replacement P5P800 MB from ASUS. The SATA controller did
not work on the first one replacement and now on the second replacement I
cannot make the Intel cpu fan speed up even thought the cpu temperature goes
to 62 degrees C when I am running a cpu intense program like DVDShrink. I
have tried the BIOS setting: CPU Q-Fan Control - Disabled and I have also
tried the BIOS settings: CPU Q-Fan Control - Enabled, CPU Q-Fan Mode - PWM,
CPU Fan Ratio - Auto. Nothing much seems to change, the fan never speeds up
even though the cpu temperature reported by ASUS Probe climbs to 62 degrees
C. I know the fan on the original MB would try to "take off" when I ran
DVDShrink. What am I missing or do I have yet another defective refurbished
MB?
Pg.59 here, mentions that the PWM control and the thermistor in
the Intel fan, both work to control the speed. The thermistor
ramps fan speed between 30C and 38C case air ambient. The PWM
control is used by features like Q-fan, to ramp the fan speed
when the CPU die temperature hits 50C. The voltage to the fan
is gated by both processes (so a low case temp and a high CPU
temp, means a low fan speed). At least, as far as I can tell
from this description on PDF page 59:
http://download.intel.com/design/Pentium4/guides/30255304.pdf
What you would have been hearing previously, is Qfan cranking
up the PWM percentage, when the processor die temp went over
50C. If your computer case now is a lot cooler than previously,
then the ramp will not be a big change. If the case air is at
38C or higher, the fan control range via PWM should allow
the fan's maximum speed to be achieved.
PDF page 133 here, shows various circuits for the fan. Asus
has probably incorporated both the top left circuit and the
middle left (four pin) circuit. When the user selects "PWM",
the PWM lead receives a ~25KHz signal (signal is constant
frequency, but variable duty cycle square wave), and the
12V pin is given full 12V feed. When the user selects "DC", the
PWM lead is not used (probably floats high), and the voltage
level on the 12V supply to the fan header is adjusted by
the two transistor switching circuit. Asus does this, so they
can support both three pin fans and four pin (retail) fans.
http://www.winbond-usa.com/products/winbond_products/pdfs/PCIC/W83627EHF_EHG.pdf
How do you debug this crap ? Good question :-(
I would take a voltmeter, and probe the +12V wire on the
Intel retail fan. This should be pretty close to 12V when
in PWM mode. In DC mode, with Q-fan disabled, maybe you'd
see 11V or more. In DC mode, with Q-fan enabled, it might
drop as low as 7V.
If you had an old analog meter, connecting it to the PWM
signal might show +12V if PWM was disabled and high 100%
of the time. A lower voltage might show when PWM is enabled
and a less than 100% duty cycle square wave is being used.
I would expect a digital voltmeter to give a garbage reading
if PWM was running, and read a stable +12V if PWM was
not running.
Have you tried the "DC" setting with Q-fan disabled ? With
PWM floating high, I would hope the Intel fan would run
as fast as the thermistor would allow. At 38C case air
ambient or greater, that should be at the fan's maximum
speed.
Paul
