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laptop power fault: compaq presario C300EA

Discussion in 'Electronic Repair' started by tg, Feb 17, 2009.

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  1. tg

    tg Guest

    I have a Compaq laptop Model Presario, service tag C300EA that will not
    start. It's this one: http://www.microdevices.lk/images/Laptop.jpg
    the motherboard is an IBL30 LA-3324P and they retail for about £125.
    ouch
    The problem is when I plug a power supply into it and press the on/off
    button the power led flashes rapidly for a few seconds and then cuts
    out. I then have to wait about a minute before it will light up again.
    I've tried three different power supplies, one of them coming from a
    battery/voltage converter and all three power supplies produce the same
    fault on the laptop so it's not the power supply. It acts the same with
    or without a battery fitted. When the power supply is plugged in I did
    notice the battery icon flickers all the time with no battery in.
    I also connected an amp meter to the power supply and when the power
    light does flicker there is virtually no current draw into the laptop.
    I split the chassis to take a look and saw that the power socket wires
    go straight onto the motherboard. There is no power board or
    daughtercard as such..
    does anyone have an idea if there's a known component that causes this
    problem? or is it a case of new motherboard?
    thanks for any pointers.
     
  2. Rich Webb

    Rich Webb Guest

    Perhaps the plague? No, not THAT one, THIS one:
    <http://en.wikipedia.org/wiki/Capacitor_plague>

    Worth eyeballing since you already have the main board exposed.
     
  3. Guest

    The symptoms suggest a short on the mainboard, the PSU aren't able to
    regulate so their protection circuits are cycling them off as best
    they can (at the price-point of the design).

    There isn't much you can do at this point except strip the mainboard
    down as much as possible. Disconnect hard drive, optical, memory, CPU
    (except if you take the heatsink off and it was heatsinking the
    chipset, you must put that heatsink back on and ensure it makes good
    contact with the chipset still), card reader, screen, inverter board.
    See if it will then "seem" (since you have no screen, watch the power
    LED(s)) to stay on. It may not, without a processor and memory. If
    necessary put those back in and retry. If it stays on, reconnect
    screen but not the backpanel lighting inverter yet. If it turns on
    and stays on, see if there is output to the screen by shining a strong
    flashlight on it.

    If it works this far, an inverter failure is a common cause. If it
    didn't work at all up to this point, mainboard probably needs
    replaced. If it works up to some point in the middle, suspect the part
    (s) you added at that point. These days such a problem is typically
    handled by replacing the mainboard at a repair shop, then if that
    doesn't work they replace the next part and so on, till it's fixed or
    the customer refuses to pay for their diagnosed problem since often
    the laptop cost little more than the total repair cost.
     
  4. Conor

    Conor Guest

    Didn't think laptops used electrolytic capacitors...
     
  5. hr(bob)

    hr(bob) Guest

    What did you think they used for capacitors in the power supply?
     
  6. jakdedert

    jakdedert Guest

    They're surface mount, so you might not recognize them. Google is your
    friend....
     
  7. Guest

     
  8. Guest

     
  9. Conor

    Conor Guest

    Grasping at straws.

    That's not remotely related to the problem is it?
     
  10. Conor

    Conor Guest

    I wouldn't buy any laptop using electrolytics other than in an external
    power brick.
     
  11. Rich Webb

    Rich Webb Guest

    The battery (or external supply) sources one voltage. The main board and
    peripheral components require multiple, regulated voltages. Therefore,
    somewhere there are several DC-DC converters to supply those voltages.
    Those regulators will likely use tants or low ESR aluminum
    electrolytics.

    The OP is having problems with a "laptop power fault," therefore
    *something* is likely wrong in a power stage.

    Capacitors in the power stages are rather more likely to fail than
    inductors or (properly rated) semiconductors, therefore it's worth
    examining them for no other reason than crossing them off the list.
     
  12. Guest

    Check that it's not the Compaq model that used RAM for BIOS and dies
    when the backup battery gets low.
     
  13. Jerry Peters

    Jerry Peters Guest

     
  14. Jerry Peters

    Jerry Peters Guest

    Had a problem like that with an old Dell laptop. Measuring the
    resistance across the power input jack showed a direct short. After
    disassembling the unit I found an electrolytic across the power lines,
    after the rf filter & fuse that was shorted. Removed it and the laptop
    now works fine (so much for no electrolytics in laptops).

    Jerry
     
  15. Guest

     
  16. Guest

    By that I meant no internal power converter board that's separate, it
    does have a separate input jack board (also without caps, it's only a
    strip big enough to hold a couple jacks), and the brick AC-DC adapter
    separate as with practically all laptops in the last several years.
     
  17. Guest

     
  18. Guest

    Now you know one of the reasons why they don't typically put
    electrolytics in laptops anymore. I never suggested no old laptop
    ever had any, but this is a pretty modern laptop not some ancient Dell.
     
  19. bz

    bz Guest

    wrote in :
    Two light tan, near left bottom corner, ~1/4 distance to top edge and ~1/8
    distance to right edge, with brown polarity bands, opposite polarity, bands
    out.

    There are almost certainly others but resolution insufficient.

    I see at least 3 on the bottom view, one near the top edge center and two
    near the bottom edge center, partially hidden by a wiring bundle.

    Any cap over 10 uF will probably be electrolytic.




    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  20. Conor

    Conor Guest

    There speaks someone who knows **** all about electronics. If you did,
    you'd know why electrolytic caps in a laptop is generally considered "A
    Bad Idea".
     
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