last resort for fixing a laptop motherboard

Discussion in 'General Electronics Chat' started by bobofett, Jun 10, 2010.

  1. bobofett

    Thread Starter New Member

    Jun 10, 2010
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    EXTERNET, I must admit that I wasn't commenting on the topic, but I didn't want to start another thread...but just ask you a question about something you wrote quite a while ago on a post (and I can't message you directly).

    topic: Fixing short circuited laptop motherboard. Where to start?

    you said as a last resort to find a shorted component one could do the following:
    Can you elaborate a little bit on how to hook up computer to car battery? Do I need to have the laptop all put together...or do I need to have it stripped down to just the motherboard (which is how it is right now). For I'm at the point of throwing away my Dell Vostro 1500 because :
    You plug in your ac adapter into the wall ac power outlet; the light on the ac adapter is solid green at that time. As soon as you connect the ac adapter’s plug into the laptop the light on the ac adapter dims and does not show green light at all until the next time you unplug the ac adapter from the laptop and from the wall. At the same time system does not power up from the ac adapter. Again if the light goes out and does not blink that also means a short on the motherboard. (A quote mostly from laptoppowerrepair.net)

    For I need a way to determine if the motherboard is dead, if so then I can have someone fix it...or if it is something else. Trying not to spend any money on diagnosis...because I'd like to spend money on repair, or a new laptop.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. Externet

    AAC Fanatic!

    Nov 29, 2005
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    That response of mine you refer to, was probably tailored to whatever explanation of symtoms the original poster had, and the 12V instead of other volage was also probably selected by the same reason.

    For your case, whatever voltage applies could be atemped as a very last resource.

    The switching power supply for your laptop shuts off itself if encounters an overload or short. A car battery is a very brute force last resource to force current and blowup a short, if a short circuit is the proplem.

    How to connect? Battery + to laptop power input +
    Battery - to laptop power input -

    For a laptop that uses 12VDC or more supply. Doing it with the laptop buttoned, you will not detect which component is the source of smoke.
    Remove before all pluggable items as CD, HD, its battery, cards...

    It won't fix it. May tell what is shorted (or was) !
     
  4. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    A three year old laptop might need to be replaced but unless it was badly or very heavily used it should be worth fixing.

    Eliminate the easy stuff and things that are prone to fail.
    Do you know that the AC adaptor is good? That green LED could be telling lies and the Adaptor could have problems. If it is starting to fail open then it could have too much internal voltage drop under load.

    Multimeter testing might spot this. Easier would be to try another power adaptor for example a car adaptor if you have one, or a docking station.

    Is the problem in the laptop battery or charging circuits? Laptop batteries are expected to fail. If your battery is more than 3 years old and has seen regular use I would consider getting a replacement. A badly shorted battery and charging circuit could cause a failure to work on AC power - but they should be automatically isolated so that you only get a message in the Laptop OS telling you that your battery needs to be replaced.
    You didn't mention that you had gotten any of those messages and battery failures tend to be gradual unless the battery is damaged. You would likely have noticed sharp drops in battery power unless it was a very bad battery.

    This is the simplest check because the laptop can be booted up with the battery removed, and if it does it was a bad battery - and you should look at getting a new battery immediately.

    I don't recommend trying to smoke out your problem. It is very likely something will smoke but not always likely that it will the same part that caused your original failure. This is an old troubleshooting technique and valid but only to be used if you planned to throw away the laptop anyways.

    Better is to start disconnecting everything.

    Hard drive, Ram, CDrom, possibly even the screen if you have the technical skills and an alternative method of seeing the system boot-up like a USB vid card connected to an external monitor.

    The Hard drive cooked and shorting is a possible cause, but it would need to have taken out some other parts with it before you get the situation you describe.

    A Dead Processor is also possible especially if you remember your laptop running hot and you used it very frequently.

    Do some general due diligence and put all capacitors under a magnifying glass. They have some of the highest failure rates. Most of the time there will be bulging on one of the small Electrolytics to show if they have gone bad. These are always a suspect when you have power problems.
     
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