A7V333 problems and power supplies

Discussion in 'Asus' started by John Wilson, Jul 17, 2003.

  1. John Wilson

    John Wilson Guest

    Ordered three A7V333 (rev. 1.02) boards back in December. (I am running
    a Athlon 1700+ (0.13um) CPU in these boards.)
    Didn't have time to set one of them up until recently, and the other was
    only used a little. The one I setup in December had to have the power
    supply replaced in Feb. The 3.3V portion of the supply (300W) was
    putting out 3.9V. I lost a SCSI controller. Replaced the supply and all
    worked well until recently. Then the power supply started to make high
    pitched noises. Not the fan, but very high freq. like a fly-back
    inductor in the switching power supply that had a large switching
    current flowing through it causing magnetostriction of the magnetic
    core.

    Then....
    I built another machine using one of my other boards and new CPU (same
    speed and also 0.13um). The box for this machine is an Antec with a 350W
    supply. It ran for a little less than a day and then started the make
    the same (more or less) high pitched sound. Now that machine reboots and
    gives trouble.

    My conclusion is that ASUS screwed up the on-board buck converter (the
    DC-DC converter used to step the 3.3V from the power supply down to the
    CPU voltage ~ 1.5V to 1.8V depending on CPU) and that is producing large
    ripple currents in the fly-back inductor in the 3.3V output, which is
    probably causing the output filter capacitors of the 3.3V section to
    fail since they are probably seeing large ripple current as well.

    The interesting part is that we have a machine in the lab that I built
    using a rev.1.02 A7V333, but it is using a 1900+ Athlon that was
    fabricated in a 0.18um process. This machine has given no trouble. It
    could be that the on-board buck converter produces large ripple currents
    when stepping down to the lower voltage that is used by the 0.13um CPU.
    I wouldn't draw such a conclusion, except that I have encountered it
    twice with 0.13um CPUs, but when a 0.18um CPU was used I have had no
    problems.

    I have ordered a 0.18um CPU so that I can experiment at home (the lab
    machine is not mine to experiment with) and I have a new and unused 350W
    supply to experiment with too.


    Has anyone else had similar woes?

    Please reply to the newsgroup and my email address.


    Thanks in advance.

    John Wilson
    Ph.D. Electrical Engineering
    Visiting Research Scientist
    North Carolina State University
    Electrical and Computer Engineering Deptartment
     
    John Wilson, Jul 17, 2003
    #1
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  2. John Wilson

    Paul Guest

    There is a table of processors here:

    http://www.qdi.nl/support/CPUQDISocketA.htm

    Have you set the Vcore voltage correctly for the processors you are
    using ?

    Has anything failed completely ? As in a burst capacitor or leaking
    brown fluid onto the board ? Abit boards like to fail like that,
    whereas on Asus boards, we get the occasional report of a failed
    MOSFET (burned and cracked).

    Usually when Asus screws up a Vcore design, the result is frequent
    processor crashes due to insufficient current or wobbly output voltage.

    I think with the A7V333 it is easy to apply too much Vcore. There
    is an overvoltage jumper, that bumps Vcore 0.3 above nominal. You should
    be able to use the Power Monitor BIOS page, to read the voltage,
    or get your trusty voltmeter, to make sure it isn't overvoltage.

    DDR DIMM voltage jumpers and mention of the overvoltage jumper:
    http://www.spodesabode.com/content/article/a7v333/print

    Overvoltage is mentioned here also:
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=a8ka11$spu21$

    Lostcircuits says it uses an Onsemi NCP5322A for Vcore (because I cannot
    read the part number on the chip in the picture of the board in the PDF
    user manual):
    http://www.lostcircuits.com/motherboard/asus_a7v333/3.shtml

    Onsemi says the NCP5322A regulates 12V down to 1.6V at up to 45Amps
    (with the Onsemi reference circuit, presumably). Could the sound
    you are hearing actually be coming from the computer PS as it
    supplies the +12V ?

    http://www.onsemi.com/pub/Collateral/NCP5322A-D.PDF

    Now you can check the Asus designer's calculations :)

    Paul
     
    Paul, Jul 17, 2003
    #2
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  3. John Wilson

    ... et al. Guest

    Both the A7V333 1.01 & the 1.04 i've looked at have location U8 occupied
    by an Onsemi NCP5322A.
     
    ... et al., Jul 18, 2003
    #3
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