Northbridge Overheating?

Discussion in 'Mac Pro' started by spiffyfitz, Mar 24, 2008.

  1. spiffyfitz macrumors newbie

    Aug 16, 2006
    Today I got back to my dorm from Spring break. When I turned on my Early 08 Mac Pro that has been off for 10 days, the fans kicked into high gear on startup like normal... then a few seconds later, they went into overdrive and are very, very loud. The fan on the rear by the RAM slots appears to be making the most noise.

    I rebooted and unplugged the thing for a few hours... no luck. Upon glancing at my Activity Monitor, only 0% - 1% of CPU is ever used by anything... and it's usually Activity Monitor. However, iStat Pro indicates that my Northbridge Temp Sensor is reading 259º F. That is way too high.

    I can't figure out how to resolve this problem. The one small black visible heatsink on the motherboard is only a little warm at most. Can anyone help?



    Resetting PRAM changed nothing.
  2. Mr.Noisy macrumors 65816


    May 5, 2007
    erm yes 259°F is rather high, i thought mine reaching 70°F was high enough.

    Doesnt water boil at 212°F ?? :eek:

    unistall/reinstall istat pro i think that may be a wee bit buggared ;)
  3. c:\windows macrumors member

    Feb 27, 2008
    Houston, Texas
    Whats the name of the program you grabbed the screen shot from. Looks useful.
  4. Firefly2002 macrumors 65816

    Jan 9, 2008
    The monitor's clearly inaccurate, max junction temps are probably closer to 200F before the thing melts. If I remember correctly, the max juncture temp on the PowerPC 7400 was 168F before it failed... and that, I believe, was when it wasn't in operation.

    Lol, it still gets me that Macs now have a Northbridge. How odd.
  5. c:\windows macrumors member

    Feb 27, 2008
    Houston, Texas
    never mind I should read closer "istat pro"
  6. trainguy77 macrumors 68040

    Nov 13, 2003
    I would see if temperature monitor gives you the same reading. It could be the sensor thats gone causing the fans to crank up. If temperature monitor gives you the same reading then i would shut it down. Wait for it to cool %100 then boot up and check the temperature and see if its the same.
  7. jjahshik32 macrumors 603

    Sep 4, 2006
    Personally I dont keep istat pro installed on my mac pro, it seems to always have something go wrong.
  8. itsallinurhead macrumors 6502


    Apr 23, 2007
    Southern California
    istate menus is pretty awesome.
  9. CamaroRS4me macrumors newbie

    Mar 16, 2008
    well... a quick google search took me to an intel page... the temp juncture on most all of the Core 2 Duo processors are 100C (212F).... doesn't list the northbridge and I know the pros are on xeon processors..... so I think either your sensor is messed up or the program is reporting wrong lol
    +1 on the istat menus too
  10. spiffyfitz thread starter macrumors newbie

    Aug 16, 2006
    even if it's reporting wrong, why are my fans on full blast no matter if i'm at EFI boot prompt or in windows?

    How can I slow the fans?
  11. Infrared macrumors 68000


    Mar 28, 2007
    I would run the Apple hardware test.
    To do so: reboot from the hard disk and hold down D.
  12. ralfi80 macrumors newbie

    Mar 14, 2008
    Bremen, Germany
    I think iStat pro doesn´t show the wrong value. Even the BIOS of the MAC thinks the Northbridge is overheated, so the fans are rotating on maximum.

    But the Northbridge isn´t at that temperature otherwise it would be broken within short time.

    Obviously the temp. sensor seems to be defectively. I don´t know if the sensor for the Northbridge is inside the chip or on the mainbord, but the only way the solve your problem is to take the MP back to apple.
  13. dukeblue91 macrumors 65816


    Oct 7, 2004
    Raleigh, NC
    I second that!
    Pack that bad boy up and go to Apple if you have one near by.
  14. spiffyfitz thread starter macrumors newbie

    Aug 16, 2006
    Hm. This is highly unfortunate. I will call Apple in a few hours to set all of this up. Thanks for the help!
  15. Infrared macrumors 68000


    Mar 28, 2007
    Apple probably won't accept what iStat says.

    Try the hardware test. It's found sensor errors before.
  16. spiffyfitz thread starter macrumors newbie

    Aug 16, 2006
    bumping for a brief followup of my mac pro adventures:

    Took this thing to the Apple Store in Rochester, NY... not an easy task without a car and living an hour and a half away at the time. A few weeks later I got it back from a friend who picked it up for me. Plugged it in... no dice. Same symptoms, Apple essentially did nothing.

    About a month later, tonight to be precise, I take it to the Apple Store in Buffalo, NY. Again, this is difficult for me because I don't own a car. Before I took it home we hooked it up at the Genius Bar and made sure everything worked. Their Cinema Display they used flickered for a little bit and stopped when i re-detected displays. I figured this was just an old display and it was just warming up. I got some silver thermal grease on my hand that whoever worked on my computer forgot to wipe off. I went in the employee bathroom to wash it off... That stuff is messy, no big deal. Ah, good, everything works fine and the machine is silent...

    ..Until I hook up my machine at home. Now it's like sitting next to a turbo fan again. The machine was silent for a good 5 minutes first, however. And during that time I watched my iStat widget do its thing. It was reporting the Northbridge temp at around 113 - 127, fluctuating slowly. I loaded up World of Warcraft to see what happens... it bumps up to 160 and hovers there. Unload WoW, and it goes back down. I play a mp4 movie file for about 5 seconds, and the temp flies up to 259 again as the fans kick into high gear.

    I fiddled with my 8800 GT to see if that was the problem. I unplugged it and plugged it back in. Maybe it just needed to be reseated and this whole problem would be fixed? The machine was silent again for about 3 minutes until it became loud again.

    This is the second time Apple has failed me. I'm getting very ticked off and I'm on the verge of asking for a refund. Hell, with the money I would get I could buy a car. More story to come as it unfolds...
  17. tobyg macrumors 6502a

    Aug 31, 2004

    My friend recently had this problem with his Mac Pro, but this was one of the original 2006 models so I'm not sure how much different the 2008 model is. So keep that in mind, I'm speaking of the 2006 model. His is way out of warranty (no Applecare) so we got to play with it without worry of voiding an already nonexistent warranty. We did 2 things, one of which fixed it. I'm not sure which.

    The heat sink that was reporting the problem is actually the one in the memory bay, not the one visible near the PCIe slots. This is also called the MCH, memory control hub, or North Bridge On the 2006 Mac Pro, with the 8800 installed, the cable for the temperature sensor on the heat sink is RIGHT below the front of the 8800 card when installed in slot 1. You can unplug that cable and it should say MCH underneath it. I would try to unplug that plug (it's only 2 wires) and plug it back in and see maybe if its just a loose connection.

    We also actually completely removed the heat sink (not an easy task, not going to get into how to do that as your machine is under warranty still) and reapplied some new heat sink compound (AS5, Arctic Silver 5). We then reassembled everything and his machine is now working just fine.

    Underneath the heat sink is thermistor attached via some sort of an epoxy. We did not remove that from the heat sink at all, just removed all of the old heat sink compound and reapplied a nice thin coat of AS5.

    So either the act of replacing the heat sink compound or just removing/reseating the cable to the thermistor fixed his problem.

    My guess in his case is it was just a loose connection. The heat sink was almost cold to the touch with the fans running full blast but istat still reading 259 degrees. Impossible. My friend seems to believe it was more related to the heat sink compound. But the heat sink compound doesn't get near the thermistor. The thermistor us underneath the heatsink but not near the heat sink compound.

    So anyway, just try removing that cable and plugging it back in (when the machine is off and unplugged from the power source, of course). If it happens to my friend again, we'll probably see if we can just order a new heat sink. My guess is the heat sink would come from Apple with a new thermistor already attached. Worst case, it's the motherboard connection to the thermistor that has the problem.

    I hope this makes sense. Sorry I'm all over the place with this reply, but maybe it will give you some ideas.

    And remember, everything mentioned above is referring to a 2006 Mac Pro. I have not seen a 2008 Mac Pro up close so I can't tell you if it's the same or not.
  18. ecorb macrumors newbie

    May 22, 2012

    I've been trying to correct the full-speed fan syndrome on my mac pro (2008 2.8 quad core) for months now. I finally downloaded and installed iStat, then saw that the "Northbridge" temperature was way higher than any other temp (it typically ramps up from 140 to 259F).

    What fixed it finally was simply disconnecting and reconnecting the northbridge heatsink-to-motherboard connecter. It is a simple two-prong connecter just left of center in this photo: You can perform this without tools, but tweezers or needle-nosed pliers may help. There is no 'latch'.

    Perhaps a weak connection there led to erroneous resistances and a false temperature reading.

    The connecter is easily accessible by just taking the side panel of the computer off and removing the video "card".

    The Northbridge temperature is now stable around 122F, more in line with the other temps.

    It's kind of embarassing what I went through in the way of troubleshooting, but let's just say I wish I'd started with iStat six months ago.

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