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    CF-28 is making "buzzing" noise when power attached

    Discussion in 'Panasonic' started by kodi, Apr 15, 2008.

  1. kodi

    kodi Newbie

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    Hi guys.

    This is my first post here, so I want to say Hello All :D
    I bought two CF-28 STJGEDM. One is working good (except microphone, but I have to check if it has one). The second one has problem with powering up - in a little strange way indeed. When no powersource is attached (battery nor AC adapter) and then I connect battery (or AC adapter) and quickly (in up to 3 seconds) push the power switch - Toughbook is working normally. It goes to sleep, I can wake it up and so one. As soon as I completely shut it down - it cannot be powered up again. It makes some kind of "buzzing" "whining" noise, that comes from the right side of laptop. I tried to locate the source of it and no success at this moment. When there is no power source attached and I connect it and will not press the power switch, after few seconds situations is the same - "buzzing" noise, and no reaction to power switch turning.

    As I have a keyboard to replace in this unit I will be opening it, so if anyone has any idea what to look at - please post it here.
     
    kodi, Apr 15, 2008
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  2. mnementh

    mnementh Crusty Ol' TinkerDwagon

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    What you describe sounds like an overloaded switch-mode power supply circuit - either in the MB power supply section, or in the inverter board in the LCD. Either one can cause the MB to go into shutdown. I would suspect a leaky electrolytic capacitor; either dried out & gone high ESR, or shorted/partially shorted internally.

    This is a case for component level diag; time-consuming & mostly guesswork without the proper tools. (IE good multimeter, Capacitor ESR meter, maybe a 'scope)

    mnem
    *Illegitimi non capacitorum!*
     
    mnementh, Apr 15, 2008
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  3. kodi

    kodi Newbie

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    ... and probably power input, DC/DC and of course caps are part of main board. Darn. I knew that it won't be easy. I have decent multimeter, pretty steady hand and some equipment. I don't have a scope at this moment (I moved to another country). So I assume for the warmer part of this year, I'll get used to it and then in the winter - I'll hunt down the source (if it won't be too obvious just looking at it with multimeter) .
     
    kodi, Apr 15, 2008
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  4. mnementh

    mnementh Crusty Ol' TinkerDwagon

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    Well... you might get lucky using a screwdriver or disposable chopstick pressed against your ear (OUTSIDE of the ear) as a cheap stethoscope to identify the actual source of the noise; then start looking for iffy capacitors around that source...

    mnem
    BZZZZZZT!
     
    mnementh, Apr 15, 2008
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