Tyan Tiger S2725 won't boot anymore after CMOS clear

Discussion in 'Tyan' started by doozler, May 1, 2009.

  1. doozler

    doozler Guest

    Hi, I have bought a S2725 board with two Xeon's and 4 Gb. To test it,
    I connected it to a seasonic 350W psu. At startup it showed the post
    messages, ram was ok, nothing wrong
    and I could start system.
    When I tried to enter BIOS it showed a password message, that I didn't
    know of course.
    So, shut down the thing, switched off psu and reset CMOS as it said in
    the manual.
    Then I started it up again but while the cpu fans started and power
    led on, nothing happened after that (blank screen, no beeps). Any idea
    what happened, anyone? Thnx a lot.
    doozler, May 1, 2009
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  2. doozler

    The Doctor Guest

    Sounds like you need the replace the BIOS chip.
    The Doctor, May 1, 2009
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  3. doozler

    Paul Guest

    Did you unplug the computer from the wall ? The important thing,
    is that the +5VSB not be running. You can switch off the computer
    at the back, but just for safety sake, unplugging the computer
    guarantees no power is present. (One poster had a power supply,
    where the switch was broken, and the supply was still powered,
    even though the switch was set to "0".)



    In either the manual, or the picture of the motherboard, you can see
    the blue jumper to the right of the CR2032 CMOS battery. So that
    is presumably the jumper you used.

    If this is one of those motherboards, which can be damaged
    by using the CMOS jumper, the most likely component to be
    damaged, is located at 2 o'clock with respect to the
    CMOS battery. If the clip of the battery holder was considered
    to be at 12 o'click, there is a black thing with three pins on it,
    next to the battery. That is most likely to be a dual diode with marking
    of K45 on it. I have three motherboards that use the same diode
    device, and for the same purpose. The CMOS power is maintained
    through that black thing. In some cases, the damage is
    severe enough, you can see burn marks on it.

    BAS40W-05 (marking "K45" on top)

    This is what the black thing with the three legs is responsible for.
    This would be a typical circuit for it.

    | anode common cathode
    +5VSB ---- regulator ---- "3VSB" -------- diode ----+
    | |
    | +----> to CMOS/RTC
    | | on Southbridge
    CR2032 ---- 1Kohm resistor -------------- diode ----+
    | anode
    | <-- 3 legged dual diode -->

    So the diode is a path that supplies power to the Southbridge well.
    In an emergency, the tiny three-legged device can be replaced
    with two silicon diodes. The silicon diodes will have a
    higher forward drop, which means the battery may appear
    to flake out sooner. But in many cases, the silicon diodes
    may be the easiest to find locally.


    You can make a dual diode, out of a couple 1N4148's. You join the
    "banded" ends of two diodes together. That forms the "common cathode"
    lead, the center pin of the three legged device. The two loose
    "non-banded" ends, become the anode connection, the two pins
    on the other side of the device. Due to symmetry, it doesn't
    matter which anode goes to which path. They're equal.

    Naturally, you'd orient yourself with a multimeter set to volts,
    and measure the voltage on the three legs, before assuming anything.
    It could be there is nothing wrong with the K45. You'd expect to
    see 3V - 0.4V drop or about 2.6V or so, on the common cathode
    (middle) leg. If there was voltage present there, then the motherboard
    should be able to start. With the motherboard powered and running,
    you'd check the voltage again, to see if perhaps the problem
    was insufficient voltage to maintain it in a running state.

    If the middle leg isn't managing more than 2.0V, then I might
    investigate the physical appearance of the K45. Apparently,
    it fries pretty good when damaged, so you may be able to see
    the damage. One poster told me, he could no longer read the label
    printed on one of those, from the burn.

    The soldering is delicate work, and I've made a mess of a couple
    repairs. So someone pretty skilled at soldering, with a temperature
    controlled soldering iron at the ready, would be needed to do the
    repair. If you have a TV/radio repair shop nearby, consult them
    as to whether they could do it for you. They might even have
    a couple general purpose switching diodes in their parts
    cabinet, to do the emergency repair.

    Good luck,
    Paul, May 1, 2009
  4. doozler

    Paul Guest

    Another thing. Are you sure the jumper is currently in the
    correct position ?

    Paul, May 1, 2009
  5. doozler

    doozler Guest

    Hi Paul,

    I checked the D1 diode but it tested still ok. I followed the
    instruction in the manual but I'm not sure anymore
    if I unplugged the power adapters from the mb or not. At least the psu
    was switched off. The jumper is in the correct position again.
    Thanks for the explanation of the diode, I'll power it up again next
    week and check voltages when "hot".

    I can't think of any reason why a BIOS would become damaged from
    removing cmos voltage momentarily?
    Btw, my psu is 430w instead of 350w. Guess that's enough for a bare
    board with no external devices attached except a hdd.

    doozler, May 1, 2009
  6. doozler

    Paul Guest

    The CMOS/RTC shouldn't have anything to do with the EEPROM
    that holds the BIOS firmware. I don't see a reason for the
    actual BIOS to be damaged. My theory is, that the processor
    is not even trying to execute the BIOS at the moment.

    If the Southbridge is not being powered, by the output of
    that dual diode, that can be enough to prevent the motherboard
    from starting.

    If you want another experiment to try, power off completely
    again, and pull all the RAM. See if the board will beep,
    indicating a RAM error or not. If it will do that, then
    some BIOS code got executed, and the processor did some
    work. If you can get it to beep, then that is a good sign.
    Then put back just one stick of RAM, and try again.

    Paul, May 1, 2009
  7. doozler

    doozler Guest


    I managed to get it started again :)
    The things I did are these:

    1) remove all memory and start up: 6 beeps indicating Missing Memory.
    2) insert only bank 2 and 4: starts up normal and able to get to BIOS
    setup with DEL key.
    3) insert all memory: starts up normal now and able to get to BIOS
    setup with DEL key.

    I'm not sure why these steps were needed but I'm glad the thing works
    now as expected.
    Thanks for your help!

    cheers Albert
    doozler, May 3, 2009
  8. doozler

    Paul Guest

    Strange things happens some times. Good job on the debugging!

    Paul, May 3, 2009
  9. doozler

    doozler Guest

    Found out one more thing:

    After CMOS reset to default, the option Quick Boot was ENABLED ( =
    ( ?? ) According to the manual is should be off so that all (self-)
    tests are executed at boot time. Due to this, among others the auto-
    detect function doesn't work so that your attached drives are not seen
    to be present for example, unless you are very lucky to have attached
    it to the right connector. Maybe this is the reason why it didn't boot
    when reset.
    Setting the Quick Boot option to disabled, the thing performs booting
    like one expects in the first place.

    cheers Albert
    doozler, May 5, 2009
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