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Faulty Motherboard

Discussion in 'Electronic Repair' started by M.Joshi, Feb 19, 2006.

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  1. M.Joshi

    M.Joshi Guest

    Hi,

    A few days ago, our computer suddenly started to emit black smoke an
    stopped working.

    Upon further inspection, the power supply had a large hole blow
    through the case which seemed as though something had exploded and
    black 'gunky' substance leaking from it.

    We replaced the power supply and tried testing the motherboard but onl
    the fans power up. I have checked that both power connectors ar
    connected and also tried removing all peripherals and cards.

    Nothing appears on the screen and the motherboard does not even get a
    far as the P.O.S.T?

    Looking at the electrolytic capacitors near the P4 power connector,
    few of them seem 'puffed up' at the top, with a powder substanc
    leaking from the top.

    I tested the capacitors with the continuity setting on a multi-mete
    and two of them showed as a short circuit. I know testing in circui
    will not give a conclusive reading so I will de-solder just to mak
    sure first.

    I am wondering whether the short-circuited capacitor(s) on th
    motherboard near the P4 connector caused the power supply to becom
    damaged?

    Does the P4 power supply affect the motherboard's startup routine?

    I thought the BIOS would be powered from the main power connector an
    that the P4 power supply is just for the processor?

    The motherboard is a Gigabyte P4 Socket 478 GA-8IRML.

    I remember reading about Gigabyte having a problem with faulty powe
    supply decoupling capacitors a few years back
     
  2. Dave D

    Dave D Guest

    The capacitors in the power supply exploded, forcing the motherboard
    capacitors to handle unsmoothed DC.
    Yep, they're toast.
    They'll all have to be replaced, forget about testing them. There should be
    a few capacitors in parallel to give an overall large value. If one in the
    'row' has burst or domed on top then you'll have to change all of the
    paralleled caps. There's no guarantee this will fix the motherboard though,
    there may have been overvoltage which may have destroyed a lot of
    components, possibly including the CPU.

    Good luck getting those capacitors out- it isn't easy without really good
    tools like a very hot temperature controlled iron!

    Incidentally, reading a short could be normal- the motherboard draws a *lot*
    of current and the supply rail will have a very low impednace.
    More likely the other way round. It's possible though that there was a
    catastrophic failure on the motherboard, eg a shorted CPU, which caused the
    power supply to blow.
    P4 power supply? You lost me. If you mean the extra connectors and not the
    main ATX power connector. They're all tied together in the power supply unit
    itself, they don't come from a seperate.circuit IIRC.

    And others as well. It wouldn't likely cause your power supply to blow up
    though, it would just cause very erratic performance and crashing.

    Dave
     
  3. James Sweet

    James Sweet Guest


    The capacitors being shorted will definitely prevent the board from
    working, you could try replacing them but the only boards I've seen
    which have had the power supply blow up like that were toast, they had
    other bad components.
     
  4. mistermaniac

    mistermaniac Guest

    Just replace the caps that are blown or have "Rubycon" written on it
     
  5. M.Joshi

    M.Joshi Guest

    Hi,

    Thanks for all your useful suggestions.

    All the parts including the CPU have been tested separately o
    different computers and they all seem to work.

    I did try to de-solder one of the capacitors (GSC brand) that wa
    puffed up but it was really difficult using an Antex soldering iron an
    doing so seemed to damage the tiny PCB tracks.

    Incidently, the capacitors that were puffed up were around the P4 powe
    connector (Additional power for the processor).

    I figured that maybe a short on the motherboard caused the power suppl
    to overheat and one of the capacitors to blow hence delivering a hig
    ripple voltage to the motherboard and possibly damaging variou
    components?

    I think we will just purchase another P4 Skt. 478 motherboard - the
    are fairly cheap on Ebay!

    Any brands/models to avoid?

    Thanks
     
  6. Wayne

    Wayne Guest

    Hope this is not a repeat of another post - have a look at this site -
    lots of info on how to remove and install, identify bad caps, etc.
    http://www.badcaps.net/

    Wayne
     
  7. Dave D

    Dave D Guest

    I use a 50W temp controlled station and even that doesn't make the job easy.
    If you've damaged tracks forget about repairing it.
    A wise move. You'll likely have no luck with your old one.
    Not really, even the very cheap ones have given me good results. If you see
    one you like, try and find some reviews before buying.

    Dave
     
  8. Asimov

    Asimov Guest

    "M.Joshi" bravely wrote to "All" (19 Feb 06 23:05:10)
    --- on the heady topic of "Re: Faulty Motherboard"

    M.> From: M.Joshi <>
    M.> Xref: core-easynews sci.electronics.repair:358750

    M.> Hi,

    M.> Thanks for all your useful suggestions.

    M.> All the parts including the CPU have been tested separately on
    M.> different computers and they all seem to work.

    M.> I did try to de-solder one of the capacitors (GSC brand) that was
    M.> puffed up but it was really difficult using an Antex soldering iron
    M.> and doing so seemed to damage the tiny PCB tracks.

    M.> Incidently, the capacitors that were puffed up were around the P4
    M.> power connector (Additional power for the processor).

    M.> I figured that maybe a short on the motherboard caused the power
    M.> supply to overheat and one of the capacitors to blow hence delivering a
    M.> high ripple voltage to the motherboard and possibly damaging various
    M.> components?

    M.> I think we will just purchase another P4 Skt. 478 motherboard - they
    M.> are fairly cheap on Ebay!

    M.> Any brands/models to avoid?

    M.> Thanks.


    M.Joshi,

    The proper technique for removing electrolytic caps from a multi-layer
    PCboard is to snip the cap body itself close to the base, pull off the
    remainder, and then desolder the remaining pins 1 at a time. Trying to
    unsolder the cap all at once is likely to cause track damage, as you
    may have already noticed.

    A*s*i*m*o*v

    .... That was a fascinating period of time for electronics
     
  9. AZ Nomad

    AZ Nomad Guest

    I once tried to removed bad caps from a motherboard and couldn't desolder
    the pins. It was as if the leaked electrolyte had chemically welded
    the pins to the motherboard.
     
  10. James Sweet

    James Sweet Guest


    I've had reasonable luck heating the pins one at a time while rocking
    the cap side to side to free them. YMMV of course, but that worked for me.
     
  11. James Sweet

    James Sweet Guest


    It may very well have corroded them together. I suspect what happens is
    the electrolyte corrodes the solder and changes its properties,
    increasing the melting point, I've noticed similar behavior with battery
    leakage on circuit boards.
     
  12. M.Joshi

    M.Joshi Guest


    Most of the time the capacitors are soldered really close to the PCB s
    you cannot reach just under the can to cut the pins
     
  13. AZ Nomad

    AZ Nomad Guest

    Now that I think about it, I also had trouble getting solder to flow into the
    connections. It was as if I was using solder without any flux. The solder
    just beaded off.
     
  14. Daniel Rudy

    Daniel Rudy Guest

    At about the time of 2/19/2006 5:28 AM, M.Joshi stated the following:
    Through the sheet metal case?

    Yikes.
    Dead board. Better to replace it and HOPE the CPU didn't fry.
    How old is this computer?
    Uh..Yeah... The P4 power supply powers the CPU.
    You are wrong. The BIOS is a ROM chip that has the computer's bootstrap
    code in it. It is executed by the CPU. If any *ONE* of these (Power,
    CPU, CPU Support, Clock, Chipset, Bus, BIOS, etc...) is blown out or not
    functioning, then your computer will not boot.

    For example: I have a computer motherboard where the USB controller
    marked it's passing with a whole lotta smoke. Scorched the board in
    fact. Because I don't use the USB on that machine, it continues to
    function because it is not a critical part. IOW, the computer can
    function without it.

    As the story goes...

    A few years ago, a couple of people from some manufacturer in China left
    the company and took with them the formula for a water based electrolyte
    for the capacitors. They then turned around and sold the formula to
    various other parts manufacturing companies in China, Tiwain, Hong Kong,
    South Korea, etc... The problem is that they only got part of the
    formula. As a result, the electrolyte was unstable and would degrade
    rapidly at elevated temperatures before the caps blew out. You would
    get something like 250-500 hours or so out of it before you had a
    problem. Because MY computer uses a motherboard from that era, I check
    mine periodically. There is a website that details all this.



    Unless you are good with a soldering iron, It's best to replace the
    board. They are not that expensive these days.

    --
    Daniel Rudy

    Email address has been base64 encoded to reduce spam
    Decode email address using b64decode or uudecode -m

    Why geeks like computers: look chat date touch grep make unzip
    strip view finger mount fcsk more fcsk yes spray umount sleep
     
  15. Andy Cuffe

    Andy Cuffe Guest

    That's what I do. Also, applying some fresh solder will help conduct
    more heat to the connection. The thick power and ground traces to the
    caps conduct the heat away very quickly. A temperature controlled
    soldering iron is a must (the more powerful the better).

    This motherboard sounds like a goner to me. They are rarely
    repairable when they fail to post. I doubt the caps are shorted. If
    they were shorted, the power supply would shut down. A very large
    capacitance can look like a short to a DMM continuity test.
    Andy Cuffe

     
  16. M.Joshi

    M.Joshi Guest

    When testing the capacitors with a DMM continuity test off the board
    they did read as a short until they discharged and then the same wit
    the opposite polarity i.e the probe leads switched.

    We managed to test the other critical components in other computer
    (CPU, Graphics card) and luckily they work fine, so it looks like a ne
    motherboard!

    Haven't been able to test the RAM though? Hopefully it should be O.K?

    On a separate note, the existing RAM is of the 266 variety. Will thi
    work on new boards with DDR400 RAM
     
  17. Asimov

    Asimov Guest

    "M.Joshi" bravely wrote to "All" (20 Feb 06 18:37:07)
    --- on the heady topic of "Re: Faulty Motherboard"

    M.> From: M.Joshi <>
    M.> Xref: core-easynews sci.electronics.repair:358797

    M.> Most of the time the capacitors are soldered really close to the PCB
    M.> so you cannot reach just under the can to cut the pins?


    M.Joshi,

    Don't try to get under the can. Snip the can itself. It is cheaper,
    faster to replace a cap than to try salvaging it, and risk damaging
    the PCB. Caps cost what, $1? A PCB costs what, $50? Your time costs?

    A*s*i*m*o*v

    .... Who's got the Thermonuclear Welding Set? - ToddS
     
  18. mistermaniac

    mistermaniac Guest


    A.K.A. Rubyco
     
  19. Daniel Rudy

    Daniel Rudy Guest

    At about the time of 2/21/2006 7:05 AM, M.Joshi stated the following:
    Maybe. Unless the CPU has a 266 FSB, you will be better off buying the
    400. It's not that expensive, and you will see a big performance
    improvement over the 266 if you do alot of number crunching.

    --
    Daniel Rudy

    Email address has been base64 encoded to reduce spam
    Decode email address using b64decode or uudecode -m

    Why geeks like computers: look chat date touch grep make unzip
    strip view finger mount fcsk more fcsk yes spray umount sleep
     
  20. Dave D

    Dave D Guest

    Assuming you get a motherboard which supports your existing CPU then yes. If
    you want a faster CPU with a faster bus speed then some motherboards will
    support slower memory than the bus speed but with a big performance hit.
    Basically, if you're re-using your old CPU then yes, your RAM should work
    fine.

    Dave
     
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