Question about Dell Latitude C800 Notebook

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Wrong power supply

I have a Dell C840 2 ghz laptop running XP Pro which requires a 90 watt power supply . I have one that works fine. My son has a C840 1.1 ghz which uses a 70 watt power supply. He tried plugging his power supply into my machine while Windows was running and it caused a message to appear on my laptop which said that a 70 watt power supply was detected and that the machine would only run in battery optimum mode until a 90 watt power supply was used and to press any key to continue. On pressing a key my machine's monitor went blank and it locked up. I had to hard-power the machine off (held the power button for 5 seconds) then restarted with my 90 watt power supply. The problem is that I continue to get the message on startup, but with an option to press F1 to continue, which it will go ahead and boot up, but my batteries won't charge anymore. I have completely disassembled the machine (including disconnecting the cmos power supply) and reassembled several times, but I still get the message, and the batteries still won't charge. Once, after following this procedure the machine booted without the message and the battery light was flashing indicating that it was charging. However, after I disconnected and reconnected the power supply, the same old message popped up and the machine locked up after hitting any key. I suspect that it could be the onboard battery charger, but before I start looking for one I wanted to put it before the experts. Any suggestions would be helpful. Thanks

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  • Darryl Crouch Apr 17, 2007

    I read on the internet where someone who seemed to be having the same problem removed the batteries and AC power and held down the Power button for 1 minute to clear the NVRAM. I tried it, but that didn't work either. I started swapping parts from my son's machine with mine, battery charger, video, etc., but still get the same error. Someone at work has an C840 they have been canibalizing for parts and the MB is still in it. Since that's the only thing I have yet to swap I'll try that tonight and see if the problem is there.
    I reflashed the BIOS last night to no avail, but thanks for the suggestion.

  • Darryl Crouch Apr 18, 2007

    Changing the motherboard did the trick.

  • MajickMan Dec 23, 2007

    we have a C840 with a universal Targus 90W universal power supply after the original burned out and started to smell. Used a 70W for a couple of days while waiting on the 90W to arrive and now the 90W powers off when plugged in and the 70W won't charge the batteries. Anyone got any ideas other than replacing the motherboard which would not be cost affective solution.



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Hi. to me it sounds like you have blown something . Try replacing the battery or reinstall windows. If that doesnt work sorry but i dont know anything else :(

Posted on Aug 24, 2010


Rerset the bios option for the battery / power performance

Posted on Apr 08, 2008

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It sounds a little overkill but it really sounds like a cmos problem. try flashing your bios if you cant find the power options in the bios. you like to try setting the cmos to default values.

Posted on Apr 16, 2007

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