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Jim: PC crashes

Discussion in 'Electronic Design' started by Joerg, Oct 20, 2007.

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  1. Joerg

    Joerg Guest

    Hey, Jim, just read in a German NG where someone had the same symptoms.
    Thought is was the RAM modules, had them tested by a shop, RAM was fine,
    took a really good look at the mobo and saw that some caps had begun a
    slight bulge. Might be worth a look if this happens again on the
    affected PC.
     
  2. Jim Thompson

    Jim Thompson Guest

    Thanks, I'll take a closer look.

    ...Jim Thompson
     
  3. Winfield

    Winfield Guest

    It's been going around for several years now - cheap non-OSCON
    high-density caps with inferior substitute organic electrolytes.
    One doesn't always see a bulge; often the most reliable symptom
    is CPU crashes. It's generally taken that the fix is a new mobo.
     
  4. Jamie

    Jamie Guest

    Most of the time, it's cheaper than trying to replace all the caps.
    normally, all the caps are of the same vender and if one starts
    going, the others might not be to far behind.
    I understand how ever, that a couple of the chinese manufacturers
    did have problems with crappie caps and no longer are using them.

    Could be hear say, who knows.
     
  5. AZ Nomad

    AZ Nomad Guest

    All mothermakers during around '99-'02 had problems with those caps. They came
    from a single manufacturer and showed up *everywhere*. I've personally seen the
    problem on motherboards from asus, msi, intel, gigabyte, ecs, and biostar.
    I don't think any correlation between the use of the bad caps and the maker's
    nationality.
     
  6. Guest

    Eh? The fix is to change the caps.
    http://www.badcaps.net/pages.php?vid=31
     
  7. Joerg

    Joerg Guest

    It can often be diagnosed by holding a scope probe to the rails. If you
    see excessive spikes that would be the tip-off. And yes, changing the
    caps might be a bear to do. You might occasionally strip the
    metallization out and Murphy's law states that this is usually going to
    happen on the last one. Obtaining caps that fit the available space can
    also be a (pricey) adventure.
     
  8. Eeyore

    Eeyore Guest

    The caps came from MULTIPLE suppliers actually. The *electrolyte* might conceivably have had a single
    source but that's not the name on the cap.

    http://badcaps.net/
    http://en.wikipedia.org/wiki/Capacitor_plague

    Graham
     
  9. I've been fighting that problem for years. For a time, I was
    replacing ALL the caps on motheboards. I have a Pace desoldering
    station so that was fairly easy. Some motherboards have fairly sloppy
    hole clearance for the capacitor leads, so removal and replacement
    were easy. Others (i.e. Dell) looked like the caps were pounded into
    the motherboard. If I ripped out the plated through hole along with
    the capacitor, it usually indicated that I just destroyed the board.

    The first indication of trouble is usually the rubber plug on the
    bottom of the capacitor trying to wiggle out of the can. If the board
    has a number of lopsided caps, it's either the worlds sloppiest board
    manufacturer, or the caps are about to go bad. Usually the rubber
    plug shows before the top or sides bulge.

    I've tried various methods of detecting bad caps. Bulges aren't
    always a good indication. I have an old Dick Smith capacitor ESR
    tester, which is easily fooled by the large number of parallel
    capacitors. It works fine if the capacitor is independent or pulled,
    but not on the motherboard power supply bus.

    I've also tried far IR imagers. Nothing like $20,000 worth of
    borrowed hardware to repair a $100 motherboard. Some digital cameras
    can see near IR and don't work for seeing heat. That has found some
    overheated capacitors, but more often just shows the reflected
    radiation from the CPU. A finger test of the capacitors is sometimes
    effective. If the cap is warm, it's bad.

    I've tried to use a scope to detect the expected noise on the power
    supply lines, with little success. All motherboards have some noise
    on these lines. The point of measurement (and grounding) have a huge
    effect on this noise level. Making an accurate determination is
    difficult.

    The degree of failure is also somewhat entertaining. I've seen
    motherboards with severely bulged caps, that continue to function
    without incident for many months. Eventually, there's a failure, but
    the amount of damage these can tolerate are amazing. On the other
    foot, I've seen boards with only a barely visible amount of bluging,
    generate boot problems and crashes. I suspect that this is an
    indication of board quality.

    For motherboards that I just wanted to work, and didn't care what they
    looked like, I just chomped off the capacitors with a pair of very
    large cutters, leaving the leads in the mother board. I then tack
    soldered the replacement capacitors leaving about 1/4" of leads
    exposed. It looks truely unprofessional, but gets the job done
    without destroying the motherboard. I've also substituted tantalum
    caps for the low-ESR electrolytics. Although more expensive, the low
    frequency ESR is less, so fewer caps can be used. Please don't tell
    anyone I suggested doing all this.

    Drivel: See comments on tantalum ESR at:
    <http://ludens.cl/Electron/esr/esr.html>
    in the "using the meter" section. I've seen the same problem with the
    same caps. If you think we have problems with low-ESR electrolytics,
    get ready for more of the same with tantalums.

    In retrospect, it's not worth fixing the motherboard. It's just too
    much labour. If it's under warranty, get a replacement. If not, buy
    a replacement and install it yourself.

    Incidentally, I've seen some random CPU's fail along with the
    motherboard when run with volcanic capacitors. I haven't investigated
    the connection, but I suspect that non-optimum power supply voltages
    and substantial voltage spikes, might not be very good for CPU
    survival. In general, the ones that crash while booting or running
    will have this problem.
     
  10. qrk

    qrk Guest

    Just got done fixing two Sceptre LCD monitors bought in 2004. Both
    died close to the same period, about 1.5 years later. Multiple bulging
    electrolytics on the outputs of the low voltage switching supplies
    were the culprit. I've also seen a oozing capacitor on a View Sonic
    monitor cause problems. That was the cap on the output of the mains
    rectifier.

    Mark
     
  11. Joerg

    Joerg Guest

    That works much better if you build yourself a little toroid transformer
    so you can measure differentially. Done that at a client on Tuesday.
    Then I needed one that goes down to a few Hertz so I took a large iso
    transformer. You should have seen the face of one engineer walking in on
    us and seeing a mains plug going to two 1N4148 and then on into the
    soundcard input of my laptop. Sure enough that also had to be the day
    the fire marshall did his rounds. I quickly tossed a rug over all that ...

    With Windows that sort of crashing is kind of normal.
     
  12. Nico Coesel

    Nico Coesel Guest

    Perhaps some MLCC (high capacitance ceramics) in parallel to the leaky
    caps may do the trick.
     
  13. Joerg

    Joerg Guest

    Depends on how many coals the switcher in front of it can throw on the
    fire because a few 1uF or 10uF MLCCs can only supply juice for a few usec.
     

  14. When those electrolytics leak, they eat the traces off the PC board.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
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