Power Mac G5 Dual 2.0 GHZ...mystery fan

Discussion in 'PowerPC Macs' started by awbazar, Jan 6, 2009.

  1. awbazar macrumors newbie

    Feb 6, 2008
    Scottsville, NY
    On a Power Mac G5, Dual 2.0 GHZ machine I have encountered the microprocessor fans taking off and running full speed when the tower has been in sleep mode. All control to bring the machine back is gone, no mouse control, no keyboard control, dark screen. The only exit strategy is to hold the power button until the computer shuts down and then restart it. Restarting it generally results in a functional computer. Once I did fail to have the screen illuminate and had no power on the mouse and the repair amounted to removing the lower CPU and switching it to the upper CPU slot. The apparently defective upper CPU produced problems when reinstalled in the lower CPU position and was removed which permitted the computer to operate satisfactorily. With the original upper CPU in the lower slot, the machine could not find the hard disk drive. Given that I do little work demanding of the dual processor mode, the upper CPU alone seems to do fine for me with no speed reduction observed. There was apparently a problem in the upper G5 CPU. A month after the repair, I am once again getting the mystery fan running during sleep mode and also got a CPU (0) failure report (Corrupt skip lists). The machine is still functional but seems to have a built-in boogie man lurking around. Any prior experience with this problem or comments would be much appreciated.
  2. buckthorn macrumors newbie

    Jan 15, 2009
    Do you have a liquid-cooled model? I was having a very similar problem recently with my dual 2 G5 (2004). The last time it happened (just before Xmas), the machine refused to start up. It turned out that coolant had leaked onto the CPU. After a bit of haggling, Apple agreed to give me a warranty exception and pay for the repairs. If you have a liquid cooling system, I would check the key components (PSU, CPU, and MB) carefully for any signs of leakage.

  3. eXan macrumors 601


    Jan 10, 2005
    But 2 GHz PowerMacs didn't have liquid cooling...
  4. OrangeSVTguy macrumors 601


    Sep 16, 2007
    Northeastern Ohio
    So you have a dual processor 2.0ghz machine with one of the processors removed? That is the cause of the fans revving. The fans are software controlled and not seeing that the other processor is in, freaks it out so they run at max.
  5. awbazar thread starter macrumors newbie

    Feb 6, 2008
    Scottsville, NY
    G5 Dual 2.0 GHZ fans run full speed in sleep mode...

    Thank you for the various comments on this problem. The 2.0 Dual has "heat pipes" in its heat sink unit which transfer heat from the microprocessor to the aluminum fins over which the fans blow air. The 2.5 GHZ, later version, used the Delphi developed water cooling system. I have not had any issue with liquids or foreign substances getting into or onto critical components. The fans took off when both processors were in place prior to removal of the lower processor. Thus, I do not believe that the removal of the lower microprocessor will induce the fan problem. In fact it was a reputable Apple dealer who moved the good lower G5 microprocessor to the upper position and suggested keeping the original (apparently defective) microprocessor on the shelf. He tried running it in the lower slot first and found that it caused other problems besides the fan issue when in the lower position. One problem was not finding the hard disk drive from time to time upon startup. Since I reset the power supply and PRAM recently on the solitary upper G5 system I have not had a repeat mystery fan problem. This might be a short term solution.
  6. TrapOx macrumors 6502

    Dec 4, 2008
    Changing a CPU to a different slot (even swapping the same two CPUs to the opposite slots) or removing one WILL make the fans run at full speed until a thermal recalibration is done by an Apple tech.
  7. silvereagle macrumors newbie

    Feb 9, 2009
    mystery fan

    Hi Awbazar. I have heard that if you replace a CPU, or move a CPU from one slot to the other, the motherboard does not identify it properly and you get the crazy fan issue. The solution is to run Thermal Calibration from the Apple Service Diagnostic CD (v. 2.5.8 if you have the June 2004 2.0 Dual G5, like me).
  8. awbazar thread starter macrumors newbie

    Feb 6, 2008
    Scottsville, NY
    Power Mac G5 Dual 2.0 GHz Mystery Fan...

    Hello Silvereaagle:
    Thank you for commenting about the need for thermal recal after a CPU swap. I read about this elsewhere and checked with the Apple repair facility where I had the repair done and they claimed that a thermal recal was done. I asked the question in such a way as to solicit an answer which was not just a confirmation of what "they should have done but didn't do and said they did". I realized the prospect for ******** and after considerable discussions with the tech at the repair place am satisfied that he is a true geek who never misses much of anything. Thank you for the information and warning all the same.

    Since the repair was done about 2 months ago I have logged 7 incidents of "mystery fan" and just held the power key till I got a shutdown and then restarted with apparently full recovery as far as I know. I'd like to know what is behind this but am inclined to think I may never know in my life time.

  9. silvereagle macrumors newbie

    Feb 9, 2009
    "I'd like to know what is behind this but am inclined to think I may never know in my life time."

    ...And now you know the true ways of the universe as a G5 user. I deal with two quad core G5's at work, that both were inoperable before I was hired. I must say that there was very little I could explain in what I did to remedy their numerous issues. I also have a 2.0 G5, which is so fickle that it is unusable. I am just replacing the logic board on that. The G5 is a powerful, but temperamental machine. There is no way to tell why your computer has the fan issue, but if you continue to have the problem a thermal calibration probably wouldn't hurt. You may also try human sacrifice.
  10. Remundo macrumors newbie

    Jul 6, 2011
    Yes they do, if you have the warning write inside the case "if you see liquid unplug computer and consult manual"...
  11. adcx64 macrumors 65816


    Nov 17, 2008
    You really shouldn't dig up old threads like this...
  12. Jethryn Freyman macrumors 68020

    Jethryn Freyman

    Aug 9, 2007
    Especially with the wrong answer.

    By the way, I had this issue with my dual 1.8GHz air-cooled model and fixed it by resetting the PMU.
  13. aednichols macrumors member


    Jun 9, 2010
    Now that the thread is dug up, I might note that some G5s shipped with this warning, but did not actually have an LCS.
  14. reddrag0n macrumors 6502


    Oct 1, 2007
    Even my DP 2 GHz without water cooling has this warning under the front inlet fans. Makes me wonder if the bottom PSU cover plates are all stamped like this to save costs.
  15. ahender, Apr 11, 2014
    Last edited: Apr 11, 2014

    ahender macrumors newbie

    Apr 11, 2014
    My fans running like jet engines solved...

    My husband has a G5 dual core 1047 model. Recently while in use it froze - reasons unknown - may have been power related but at this point it doesn't matter...

    When the machine was restarted the fans came on full blast and would not stop.

    I tore it down - CPUs w/heatsinks as a unit came off too, removed, dismantled and cleaned out power supply too. this machine was incredibly dirty (he has been properly admonished) re-assembled reset the pmu and pram and replaced the never-before-replaced on board battery. Fired her up and life was GREAT!! but then it happened... firmware was 1 rev behind... updated the firmware and POOOOOOF fans like crazy again... bummer.

    Then one of the CPUs gave out... ordered 2 more... and installed them both retaining the known-to-be-working CPU as a future backup... and I surmised that must have been why the fans were going nuts... a dying CPU..

    Of course you all know that if you replace CPU(s) you have to calibrate the fans using ASD except that it won't let you due to weird errors... unless you try this trick!!!(for my machine it is 2.5.8, different models need different versions so get that straight before you do this, I can only say this worked with 2.5.8)

    I can't say that it will work for everyone, but it worked like a freaking charm for me. After trying to calibrate the new CPUs together with no luck, I started trying combinations. First I should tell you that I was getting any number of errors running the diagnostics... all of which I took to be errant as they were CPU eeprom errors, then I got IC2 errors, fan errors, you name it, I got it as an error when trying to calibrate the fans... (sometimes the machine would boot to the OS with half the GHZ it was supposed to have btw)

    Then I realized that I hadn't really followed the directions found in the readme for ASD 2.5.8 which states that you should:

    FIRST: insert disc, hold down "c" while booting until you see the ASD "loading" screen. This boots diagnostics in OF mode which doesn't use the OS. Run all tests.
    SECOND: SHUTDOWN (NOT RESTART) the machine and reboot holding down the option key which boots the diagnostics in OS mode... right arrow until you see the option to boot OS diagnostics, click it, click the arrow key, wait a while for OS diags to come up (it may take a while so DON'T get impatient)

    I took it from there and did the following:

    THIRD: Choose only the CPU and Memory tests and run. (you should get a PASS - otherwise I can't say if this will work for you or not)

    FOURTH: SHUTDOWN the machine and start holding down the "c" key again to boot into the OF diagnostics (you don't have to choose it, it boots to this automatically)

    FIFTH: Go IMMEDIATELY to calibrate fans - you may get failures a few times DO NOT let this discourage you... One or both of the CPUs should calibrate - if and when you get success on both CPUs or a failure on one CPU but get success on another CPU DO NOT rerun calibration...

    after calibration on at least one CPU shutdown and restart normally.

    If the fans slow down but still run fast - you can now do the ENTIRE procedure again.

    Amazingly, after working on this <expletive> machine for 10 days and about 30 hours of intensive geekitude doing it...

    My machine now boots and runs SILENTLY :D

    If you are still having trouble - take out one CPU, run the above steps and then re-install the second CPU and do the steps again.. disabling one cpu via Open Firmware was not sufficient - it had to be physically removed - I don't know why...

    (ultimately the combo that worked for me was original-but-good CPU ALONE in the first position on the board (if you have it in the wrong position the machine won't boot so there's the big clue for you which spot is the first one...) calibrate using OF Diags (even if it tells you you don't need to calibrate - do it anyway) install second CPU, followed steps above which then issued error on first CPU but calibrated the second one.. go figure...)

    Tedious, yes definitely... Possible Cure? most assuredly.

    My thinking is that the OS diags reset some errors somewhere...or zeros them out, which then allows you somewhat successfully start down the path of calibration.

    Hope this helps...

    ASD 2.5.8 can be had for those willing to do a torrent of searching...

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