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DVD/HD speed on Dell C840 tanks when fan comes on

Discussion in 'Laptops' started by Tom Whistler, May 6, 2004.

  1. Tom Whistler

    Tom Whistler Guest

    DVD playback stutters horribly (both audio and video) on my Dell C840
    when the fan is on. When the fan is off, playback is perfect.
    Playback from both DVD and HD are affected in the same way. CPU speed
    setting (max matter, max performance) doesn't matter. It's just fan
    on = bad, fan off = good. It's probably not audio or video driver
    related, since file transfer speed (DVD->HD) is affected exactly
    the same way (fan on = file transfer VERY SLOW, fan off = file
    transfer normal speed).
    I've tried multiple DVD playback tools and they are all affected the
    same way.

    I don't have the latest system BIOS, in fact mine is about two years
    old while the latest is two months old.
    I'll try updating to the latest to see what happens. In the
    meanwhile, has anyone else with a C840 noticed
    this? There are tools I think which will let me change the
    temperatures at which the fan comes on. Has
    anybody tweaked this? I'd be a bit concerned about frying the CPU.
    Is there any other way to deal with
    this? It's driving me nuts, I can't watch DVDs at all on the
    Tom Whistler, May 6, 2004
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  2. Tom Whistler

    Tom Whistler Guest

    Well, no suggestions from the world at large, so I just kept digging.
    I discovered that one of the two fans on my C840 doesn't work, which
    is most certainly contributing to the laptop getting too hot and is
    part if not all of the problem.

    I downloaded the i8kfangui program which allows direct control over
    the fans on my laptop, and provides a running
    temperature/fan-speed/CPU usage display as well. I also downloaded
    the intel cpu frequency tool.

    Using these together, I determined that when the C840 reached a
    certain CPU temperature, the fan turned on high and the CPU speed
    dropped. The CPU speed drop was what was causing the DVD stuttering.

    I found I could get DVDs to play reliably by doing this:

    + manually setting the fan on high to get the temperature below where
    it turns on automatically (sometimes 60*C, sometimes 75*C), in the
    40's to 50's C.

    + hitting Fn-Z on the keyboard. This turns off the fan, sets the CPU
    speed back to max, and does some sort of "normalizing" of the
    temperature sensors.

    + Setting the CPU speed to "battery optimized". Setting it slower
    ("max battery") is too slow to play DVDs without stutter, and setting
    it faster ("max performance") gets the CPU too hot even with the (one
    working) fan on high, so the system then reduces CPU speed
    automatically which causes stutter.

    + Turning the fan on to "high" manually via the i8kfangui program.
    This will keep the CPU cool enough to prevent automatic clock speed
    reduction, so the DVD plays smoothly.
    Tom Whistler, May 7, 2004
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