HAS *ANYBODY* out there seen this PROBLEM with ASUS A7N8X-E Deluxe????

Discussion in 'Asus' started by G.L. Cross, Sep 28, 2004.

  1. G.L. Cross

    G.L. Cross Guest


    I have a new ASUS A7N8X-E motherboard which shows fan RPM as ZERO
    except for the case that the fan is actually being POWERED from the +12V
    terminal of the three-pin fan header. Now this is not a problem for the chassis
    fan; but it IS an issue with the Power Supply Fan (draws power internally
    from the PS) and the CPU fan which is a high-performance model that exceeds
    the load capacity available from the fan header (350mA ~ 740mA).

    Both the PS and CPU fans provide a fan speed sense connector for the purpose
    of RPM monitoring. The PS has wires for both ground and RPM sense. The CPU
    fan has only a wire for the RPM sense. Until I ran across this board, the RPM of
    both of these could be read out without difficulty despite the fact that they drew
    power from another source.

    I flashed the board to the LATEST BIOS and the problem still persists. Anybody
    know of a way to get around this problem? What would happen if I were to put some
    kind of artificial load on the +12V fan header output? Would the ground line also have
    to be connected?


    TO ASUS:
    Is this a design flaw or was it done on purpose? Obviously, I MUST be able to
    monitor these CRITICAL fans - otherwise I could fry an expensive PS and CPU should
    a fan go down and I'd not get any alarm (because I'd have to disable it in order to run
    with this board). Yes, over-temp should catch the CPU but by then it may be too late!!
    I don't know what protection the PS has built into it (an Antec True 430-watt).

    You may send e-mail if you wish provided it is NOT SPAM. To decode my valid
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    - G.L. Cross
    G.L. Cross, Sep 28, 2004
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  2. G.L. Cross - typed:

    Yup - seeing the same problem on my new A7N8X-E Deluxe. Neither my CPU
    or PSU fan's speed is reported in the Bios & MBM5 either shows zero or
    unrealistically high revs. Both these fans were reported correctly on my
    retired A7V266-E. Flashed from 1011 to 1012E - no difference.

    You may get a response from Asus but don't hold your breath! It could be
    a hardware fault common to both our boards of course. You should not
    need any load on the PSU or CPU fan header, IIRC. The ground return back
    to the PSU is basically there to give a noise free signal & probably
    should be OK without it at such low frequencies. Interesting that your
    chassis works - my PSU fan is the same as yours but my CPU fan is
    powered by the header via a Zalman Fan Mate. Try attaching your chassis
    fan to the CPU header to see what happens.

    As an aside, why the hell do so many m/bs have S3 power management mode
    off as a default where enabling it after OS installation usually means
    the fans will still run (S2)?
    Let them eat beef, Sep 28, 2004
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  3. G.L. Cross

    G.L. Cross Guest

    .... snipped...
    Did that, when I attach the chassis fan (which is powered from the header +12V supply),
    I get correct RPM at all three locations: Chassis, CPU, and PSU. The common thread
    I found is that you will not get a RPM reading if you power the fan from ANY SOURCE
    other than the fan header it is connected to - despite proper connection of the speed-sense
    line to the MB header...

    Also one strange thing: with a DC Voltmeter and no fan connected to one of the headers,
    I measure the correct +12V center pin to ground. But strange is that I measure a constant
    +5V between the "rotation" pin and ground. I thought the fan sent a pulse once per revolution
    AS INPUT to the "rotation" terminal (why is there a voltage on it when there is no fan???).

    - Gordon
    G.L. Cross, Sep 28, 2004
  4. G.L. Cross

    kony Guest

    Did you research the board before you bought it?
    Does it have the speadfan feature?
    Did you research this or just assume it would make no
    difference in your planned deviation from normal use?

    You can't return a board based on malfunction, when it isn't
    malfunctioning. Most people like speedfan... if you don't,
    buy a board with no fan speed control integral to it.
    kony, Sep 28, 2004
  5. G.L. Cross

    DaveyB Guest

    I'm taking an educated guess at this one concerning the fan sensor. The +5v on the rotation pin
    has very little current. When the fan sends a pulse it grounds the +5v on the rotation pin and the
    speed sensor on the MB sees this transition to 0v as a pulse. It's called "inverted logic", it's
    very common in digital circuits. The ATX power supply uses this logic it to switch on - one of the
    pins on the connector block sits at +5v - again with very little current. To switch the supply on
    the PC grounds this pin and holds it at 0v. If you ever look at a pinout of a memory DIMM, PCI
    Bus, parallel printer port or anything digital you'll come across some pin labels where the label
    has a line above it. That's inverted logic - the signal is sent by grounding the pin.

    DaveyB, Sep 29, 2004
  6. G.L. Cross

    Paul Guest

    It is also referred to as an open collector interface, or alternately,
    a wire-OR interface. Normal logic involves two transistors, working
    as a push pull pair. Open collector logic replaces the upper transistor
    with a pull up resistor to +V. When the lower transistor turns on,
    the signal on the end of the pullup resistor goes to zero volts.
    When the transistor turns off, the pullup resistor eventually
    restores the signal to +V volts. That is a logic 1 level. (When more
    than one transistor is connected to the resistor, you get an OR
    logic gate capability, as either one transistor OR the other can
    pull the line to logic 0.)

    Finding voltage on that pin is normal, and the voltage can be
    anywhere between 5 and 12V, depending on the conditioning network
    used on the motherboard. Some application notes connect the resistor
    to +12V, and then follow the output with an attenuation network, to
    get the voltage down to levels suitable for interfacing to logic
    devices. Other application notes use the simpler direct pullup to
    +5V, with no other resistors in the circuit.

    Paul, Sep 29, 2004
  7. G.L. Cross

    JS Guest

    Try connecting the ground as well.
    Connecting a DMM to digital signal is not gonna work. You need an o-scope
    to what on that signal. Plus, that may just be normal operation when the
    fan is not connected.
    JS, Sep 30, 2004
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