Did I fry something?

Discussion in 'Asus' started by Bolivar T. Shagnasty, Feb 12, 2006.

  1. OK, so I thought I'd replace the stock HSF on my A64 X2 3800+ with an Arctic
    Cooling Freezer 64 Pro, but (of course the passive heatsink on the
    Northbridge chipset was too close (A8N-VM CSM, rev 1.01), so I took it off
    and installed the Freezer according to the accompanying instructions.
    Rebooted, and all seemed well for a few minutes (except, ironically, the
    stock cooler was quieter) and then my screen went crazy with a broken,
    diagonal image of the desktop, then blank. System stayed on, with all fans
    and lights going, but nothing on the screen. Powered down immediately, and
    (you guessed it) system would not POST. No error beeps, no apparent video
    output. So, my question is, could removing that passive heatsink have
    actually let the Northbridge overheat, and if so, did I fry the onboard
    GeForce 6150?

    I tried everything I knew to get the system back up including clearing the
    CMOS, but no joy. The board has been RMA'd back to Asus, but did I void my
    warranty by removing that heatsink? I have a nasty feeling I did. I guess
    I'm wondering if a passive heatsink can make that much difference. Anyway,
    feeling dumber than I have in a while and would like some opinions on what
    likely happened. TIA.
    Bolivar T. Shagnasty, Feb 12, 2006
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  2. Bolivar T. Shagnasty

    Paul Guest

    Here is some sample data (from the Aavid catalog), for three
    heatsinks suitable for cooling a Northbridge. The figures on
    the right are in degrees C/W. Basically, the heatsink is three
    times more effective, if a fan is present.

                       Length Width Height  still  with
                          mm    mm    mm    air    fan

    35x35 374624B60024 35.00  35.00 10.00   23.40  7.55   Black anodize
    35x35 374724B60024 35.00  35.00 18.00   15.30  5.15   Black anodize
    35x35 374824B60024 35.00  35.00 25.00   12.00  4.27   Black anodize

    To work through some numbers, assume a Northbridge is dissipating
    10 watts. Using the tallest heatsink in the above table, with
    a 200 linear feet per minute flow of air from a fan, and assuming
    room temperature is 25C, we get chip_temp = 25 + (4.27C/W * 10W)
    = 67.7C . That is hot enough. Now, if the fan is removed, and the
    heatsink is in still air = 25 + (12.00C/W * 10W) = 145C. Now the
    chip is fried.

    You can imagine, that if the heatsink is removed completely, the
    chip by itself has a rating of maybe 25.00C/W or more in terms of
    cooling capability, and the temperature soars into the stratosphere.
    (25C/W estimate based on info available for an Intel ICH5 chip

    Now, the one unknown in all this, is the actual chip power dissipated.
    Some chipset companies do not make data publically available.
    Having built in graphics adds 2-3 watts to a Northbridge's power.
    Having PCI Express I/O will add some power as well. In other words,
    some of Nvidia's latest creations will be in the thermal domain where
    they really should have some cooling air flowing over the heatsink
    fins at all times. But removing the heatsink completely from a
    recent Nvidia chip, sounds like a bad thing to do.

    There were motherboards in the past, where they stuck a fan on
    a chip that had a power dissipation of only 2-3 watts. People soon
    discovered, that wnen the fan died, the motherboard ran fine without
    it. But we are no longer using those 2-3W Northbridges. The
    power level on some Northbridges is in the 10-15W range now,
    and trimming back on a manufacturer provided cooling solution
    should be done with caution. This is especially true of Nvidia
    based motherboards, where the "chipset" is only one chip (i.e.
    the Northbridge and Southbridge are squeezed into the same
    chip). A two chip solution means the heat is spread between
    the two chips, but there is still the potential for overheat
    if you mess around.

    Paul, Feb 12, 2006
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  3. William Kettering, head of GM engineering:
    "Parts left off weigh nothing, cost nothing, and don't cause service problems."

    Ergo, if the heat sink wasn't needed, it wouldn't have been there.
    MasterBlaster, Feb 12, 2006
  4. Bolivar T. Shagnasty

    Bill Guest

    Yes, I would say the northbridge chip overheated. The heatsink was there
    for a reason.

    I took at a quick look at the A8N-VM board, and I see where your problem
    with the Freezer 64 hitting the heatsink would be an issue. If you can
    swap the board for something like the A8N-E and buy an inexpensive video
    card, you'd be able to use the Freezer 64.

    If your case requires a micro-ATX board, then you'll have to find one
    that has a lower profile heatsink or fan on the chipset.
    Bill, Feb 12, 2006
  5. So, in effect, you are saying that removing the passive probably allowed the
    chip's heat to spike to a fatal point? If so, I've no doubt voided my
    warranty and learned an expensive lesson.
    Bolivar T. Shagnasty, Feb 12, 2006
  6. Yeah, the same thought crossed my mind, but obviously didn't hang out there
    long enough.......
    Bolivar T. Shagnasty, Feb 12, 2006
  7. Well, let's see if Asus decides to replace the board. If not, I might just
    go that route. If so, I dodged a bullet.
    Bolivar T. Shagnasty, Feb 12, 2006
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