P4C800-E Deluxe - CPU Fan Speed Conrol?

Discussion in 'Asus' started by Eli, Aug 25, 2004.

  1. Eli

    Eli Guest

    What mechanism controls the CPU fan speed?

    I recently built two nearly identical machines around the P4C800-E
    Deluxe motherboard. Both with P4 3.0GHz Northwood processors and
    using the stock Intel heatsink & fan with thermal paste instead of the
    supplied pad. The only real difference between the two machines is
    the case and PSU. The first machine has a larger, better ventilated
    (and noisier) case, while the second is smaller, with just one 80mm
    case fan.

    Motherboard monitor on machine A show motherboard temperatures
    typically about 32C and CPU temps 33C at idle. In the second machine
    I have similar CPU temps, but the motherboard temp usually reads about
    37C. The CPU fan in machine A is at about 2700RPM at idle and may go
    up to 3200RPM under load. In machine B I have CPU fan speeds anywhere
    from 4000RPM to 4600RPM. Needless to say, the CPU fan noise from the
    second machine is louder and the fan drone is pretty annoying.

    So, does the P4C800-E Deluxe use the motherboard temp sensor to
    control the CPU fan speed? I would have thought it would only use CPU
    temps to control this fan, which should give me similar fan speeds in
    the two machines.
    Eli, Aug 25, 2004
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  2. Eli

    Paul Guest

    The Intel retail fan, has an air temperature sensor. The design
    trip points differ, depending on which kind of processor it is,
    but basically, the fan speed is at a minimum, until the measured
    air temperature passing through the CPU fan hits 30C. The fan
    RPM rate increases until the air temperature hits about 38C, where
    at that point the CPU fan ramps up to max RPMs. The Intel CPU fan
    doesn't use the actual CPU temperature, but instead senses the
    air temperature, and attempts to compensate for the loss in
    cooling ability, of the hot case air, by speeding up.

    The motherboard has a feature called Q-fan. It can be operated
    at the same time as the Intel fan feature. Q-fan ramps up at
    a measured CPU temperature of 50C and hits max RPMs at 60C.

    When you combine the two cooling curves, the CPU will hit 50C,
    before you see any real change. With Q-fan disabled, I think you
    will see the behavior you've currently got. (4600RPM on the
    motherboard with the 37C mobo/case air temp.)
    The Intel fan is doing what it is supposed to do, on the second
    machine. If you add a case fan to the second machine, that will
    bring the case air temp down, and inside the computer, the Intel
    fan will slow down in response. In any case, AMD recommends a delta
    between case air and room air of no more than 7C. You should add
    case fans to achieve that objective. Doing so helps the most
    temperature sensitive part, which is the disk drive. The CPU can take
    more heat, and you could enable Q-fan, to quiet the second machine.
    If the processor temp is shooting past 60C, and the Intel fan
    running at full speed cannot cool it, then at the very least you
    need a better CPU cooler and/or more case fans.

    Test with Prime95 and make sure there are no detected computing
    errors, while doing your thermal testing (mersenne.org). Prime95
    will give you a 100% load and ensure you have a worst case test
    condition to work with.

    Paul, Aug 25, 2004
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  3. Eli

    Ken Guest

    Yes, in BIOS you can control the CPU fan speed.
    11/16 lowest 15/16 highest
    Ken, Aug 25, 2004
  4. Eli

    Eli Guest

    Thanks, Paul. That explains it. At the current CPU temperatures the
    fan's speed must be purely controlled by its own air temperature
    Eli, Aug 25, 2004
  5. Eli

    Formerprof Guest

    This thread induced me to check the temperatures on my P4C800E-Deluxe,
    Northwood 3.0 gHz P4. I was distressed to see that the CPU temperature was
    about 60 c. I opened the case to see whether all the fans were running and
    found that the slots on the Intel CPU fan were dust-clogged. I cleaned them
    out using a tiny Rubbermaid vacuum cleaner and the CPU temperature dropped
    back to 48 - 49 c. That's something I'll be doing every six months or so
    from now on.

    Formerprof, Aug 25, 2004
  6. Eli

    High Score Guest

    I've been told to avoid using a vacuum cleaner. The air moving through
    the nozzle can cause a static charge to build up. This charge could jump
    from the nozzle to a vulnerable component ... Zap !!!!

    You can get static controlled vacuums and also maybe could ground the
    nozzle, but I find canned air to work well without the risk.

    OTOH, maybe this is an urban legend. Anyone know of bad things happening
    with a vacuum?

    High Score, Aug 26, 2004
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