Fan Control on A8N-SLI Premium

Discussion in 'Asus' started by Derek, Nov 17, 2005.

  1. Derek

    Derek Guest

    I've just bought this board and am using 2 Nexus 120mm fans for the cpu
    and chassis fan on a amd64 3500 with scythe ninja cooler, and running
    v1009 bios. Great combination for a quiet system, but I can't control
    the fan speeds.

    I've tried Q-fan in the bios and the lowest setting that causes the fans
    to run at full speed is 51 C. When just browsing the net I'm at 33 C on
    the cpu (currently this system is not in a case), yet both fans are
    still spinning but somewhat more slowly than usual. The speed readings
    on the cpu fan is 3000 rpm, and the chassis 42187 both in AiBooster and
    same readings in Speedfan. Given that these fans are rated at 1000 rpm
    and its very clear they are not running anywhere those speeds something
    is quite amiss.

    In speedfan there is an advanced setting to reverse the output of the
    pwm - if a fan physically slows down but the speed indicator goes up -
    this is supposed to fix that - however it doesn't.

    I've tried Qfan off in the bios and run just with Speedfan - but
    speedfan doesn't seem to be able to control the speeds at all and I have
    set the temp./fan relations all up correctly.

    Two questions:
    1) is this problem motherboard specific (have others got q-fan or
    speedfan to work well) or is it due to my Nexus fans (not putting out
    sufficient speed signal voltage perhaps?) and
    2) what software / fan combinations are working for good fan/temperature

    Would be a shame to have to scrap the Nexus fans as they are ultra-quiet
    even at the stock speed of around 1100 rpm.

    Derek, Nov 17, 2005
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  2. Derek

    Dirk Pajonk Guest

    Playing around here with this features too.

    You'll have to switch the FanX Divisor from 8 to 16 or 2 to 8.
    The it wouldn't show rpm above 20000 or so.
    The it will show lowspeed!
    Dirk Pajonk, Nov 17, 2005
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  3. Derek

    Paul Guest

    The typical fan monitor hardware looks like this:

    | 8 bit interval measurement register |
    | |
    Clock --- divisor --> increment Fan_Monitor |
    | |
    | Start Stop |
    +---- | ------------------------- | ----|
    | |
    Fan_pulses ---------------+---------------------------+

    The selection of the divisor sets the time base for the interval
    measurement. If the software you use is assuming the divisor is
    2 all the time, the software will get the wrong answer on this
    programmable Asus board. To work properly, the software has to
    know what the divisor register is set to, in order to scale the
    computed result correctly.

    Fan speed measurement is determined by measuring the time
    interval between pulses, then inverting the result to get
    a frequency. When a fan runs too slow for the divisor selected,
    the interval register ends up at 255 (filled). It cannot hold
    any more counts. The software cannot tell the difference between
    a slow fan (that fills the register to 255) or a dead fan (that
    fills the register to 255 as well). That is why when a fan is
    slow, the software interprets the content of the interval register
    as meaning the fan is at 0 RPM.

    Now, why the software cannot just set the divisor to match the
    speed of the fan, is the real mystery. Architecturally, it could
    be that the software designers consider the BIOS "owns" the
    divisor register, but since software designers never discuss how
    their programs work, that is purely a guess.

    In any case, as Dirk is suggesting, if there is an option in the
    monitor software program, to set the divisor value the software
    uses for the calculaton, then it should be set to match whatever
    the BIOS is doing. The software should really be able to read
    the stupid divisor value for itself !

    Paul, Nov 18, 2005
  4. Derek

    Derek Guest

    Dirk, Paul - Thanks that was very helpful. I've got everything under
    control now, and to help anyone wondering, here are the settings I've used:

    1) Turn off Qfan in the bios
    2) Using the program Speedfan v4.27 (has more controls possible than
    Qfan): In the Advanced tab set:
    a) PWM to Software Control
    b) Fan x Divisor to 32 (at the default value of 8 I lost speed
    output below 800 rpm, it now shows speeds down to 300 rpm, and then the
    fan stops)
    c) PWMout at 3M or 12M (not very sensitive to this number)
    3) Of course set your device's temperatures to be controlled by
    whatever fans you want and trigger temperatures
    4) Also, there is a "Remember it" check box - check that so all
    settings remain in effect when you come out of a Resume.

    This should work with motherboards that have the IT8712F sensor.

    And the Nexus 120mm fans are nearly dead silent at stock 12v 1000rpm, at
    800 a whisper and well below the quiet whir of a pair of Samsung drives.
    Derek, Nov 18, 2005
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