iMac G5 Fan Whine

Discussion in 'PowerPC Macs' started by wonga1127, Apr 22, 2007.

  1. wonga1127 macrumors 6502

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    #1
    I bought a 17" iMac G5 Rev. B 1.8 Ghz off of eBay recently. The bottom fan (near the speakers) is letting off a whine. Is this normal, or am I just being paranoid?

    The whine is in the background in the audio file, because this was recorded with the internal mic. Near the middle they get louder.

    AUDIO
     
  2. RedDragon870503 macrumors 6502

    RedDragon870503

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    #2
    Those Rev a's and b's... causing trouble once again...

    Don't hesitate to bring it in to a specialist to analyze the noise and furthermore don't hesitate to send it back!

    Let the seller know ahead of time that you are investigating the noise and will get back to him with your findings.

    Drew
     
  3. Daveway macrumors 68040

    Daveway

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    #3
    This affects (in my experience) about half of all Rev A and Rev B iMacs. Apple doesn't really have a fix for it and I've just had to grow accustomed to it. If you search the web there are thousands of people who have modded their iMacs to be quieter.

    Temporary relief would be to cover the left portion of the air intake. You'll notice a difference if you put your hand over it.

    The problem is the fan and its housing running at an awkward frequency and vibration. I have a bad motherboard from Apple and the fans run full bore all the time, I'm hoping for a quieter replacement next week.
     
  4. monke macrumors 65816

    monke

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    #4
    Mine are pretty much the same way. They'll get loud for just opening Safari or something like that. I'm used to it now, but it still gets annoying from time to time.
     
  5. Cybix macrumors 6502a

    Cybix

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    #5
    my kitchen mac (iMac 20" G5) has a slight whine when it's on... doesn't really bother me too much, I figure it's normal...
     
  6. Eidorian macrumors Penryn

    Eidorian

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    #6
    The fans in the Revision A/B iMac G5 are user replaceable. If you have a friendly Mac repair shop nearby you might be able to order some.

    It does sound normal operations to me though. What was the CPU usage when you recorded this clip?

    iStat Pro can shed some light on this and more.

    And failing all that you could just open the bugger up, remove all the fans, and then clean them.

    ~desu
     
  7. wonga1127 thread starter macrumors 6502

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    #7
    My CPU jumps to about 50% when I open dashboard, which is how I made the fans speed up when I recorded the audio.
     
  8. Eidorian macrumors Penryn

    Eidorian

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    #8
    Is your CPU performance set to Highest?

    Is the sound present at very low CPU usage?
     
  9. Daveway macrumors 68040

    Daveway

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    #9
    O RLY?

    I don't recall Rev. A being user replaceable...
     
  10. Eidorian macrumors Penryn

    Eidorian

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    #10
  11. Daveway macrumors 68040

    Daveway

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    #11
  12. Eidorian macrumors Penryn

    Eidorian

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    #12
    True, it still easily removable by the user.
     
  13. Daveway macrumors 68040

    Daveway

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    #13
    Maybe members like us, but the average consumer probably doesn't want to remove the motherboard to get a fan out. I've done it.
     
  14. wonga1127 thread starter macrumors 6502

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    #14
    I have my CPU settings at highest.

    And the lower fan is the culprit. It is also easily removable. Replaceable? Nope. I struggled for half an hour to get the damn thing back in, but maybe I'm just being stupid.

    Apple has no replacement fans, at least according to their website. The only ones the user can replace are the upper fans (hard drive and system fans). I plan on going to my local Genius Bar, but I don't think I'll get much help there either.
     
  15. Eidorian macrumors Penryn

    Eidorian

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    #15
    The lower fan does not require the logic board to be removed. It is held in by a simple latch. You do not even need to use the suggested screwdriver.
     

    Attached Files:

  16. Daveway macrumors 68040

    Daveway

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    #16
    Its not that easy. At least the two machines I've worked on haven't done that. Only the left side comes up.
     
  17. johnsawyercjs macrumors member

    johnsawyercjs

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    #17
    iMac fan noise

    I fix Macs daily (since 1985), so I thought I'd give some info here.

    In the first and second iMac G5 models (the second being the Ambient Light Sensor (ALS) model, otherwise known as rev B), removing the lower fan (some people call it the CPU fan, since it sits directly below the CPU, directing air up into the CPU assembly, but Apple didn't call it the CPU fan until the iMac G5 iSight), actually is as easy as the diagram that Eldorian posted--you just remove the iMac's back cover, and then remove the fan. It's the same in rev A and rev B. If anyone finds it difficult to remove, either they're not doing it right, or it's stuck in some way, requiring some care to remove. As I type this, I've got an ALS model on my lap, with the back cover removed, and I've just removed the lower fan--it was easy. There is a small tab that can get in the way of its removal, along the lower edge of the iMac's housing, but you clear this as you remove the fan, by pushing the fan towards the CPU as you lift up on the fan--it's easy to see this tab as you do this, so you can see whether it's snagging on the fan. iMacs that have a built-in iSight camera have CPU fans that are a lot more difficult to remove, requiring a lot of parts to be removed first. Real dumb design.

    Apple may not sell the lower fan/CPU fan to the end-user, but it can be bought from various third-party Mac parts companies.

    Also, we need to distinguish between different types of iMac G5 lower/CPU fan noises. The noise these fans can make when they're defective, can be a buzzing sound, a rumbling sound, an unusual whining sound (different from a high-speed fan noise), etc. But these are relatively cheap fans, and so a lot of them can buzz when they're running fast. As Daveway says, these sounds can be due to a problem with the fan and its housing running at an awkward frequency and vibration. The sound these fans make when they're not defective, but are just running fast, is a whooshing sound, sometimes called the "vacuum cleaner" sound; be careful not to interpret this sound as a whining sound--it it's whooshing, it's not technically just a whining sound, and has a different cause. But if the fan is running fast, then you're more likely to hear a buzzing sound if the fan is imbalanced--if the fan were running at a normal speed, you wouldn't hear the buzzing unless the fan was really defective/imbalanced. If the fan is running fast, it's not because it's defective, even if it's also buzzing, so replacing it won't help the fast fan problem. In other words, there can be fans that are both defective (making a buzzing, etc. sound) AND running too fast--replacing these might just solve the buzzing, etc. noise problem (as long as you don't get another noisy fan), but not the fast fan noise problem. The recording that wonga1127 posted, sounds to me mostly like a "normal" fast fan whooshing sound, combined with a little abnormal buzzing/whining sound, so it's likely his logic board has a problem, and his fan is a little buzzy when it runs fast.

    Covering the lower fan intake, as Daveway suggests doing above, is NOT the solution to the fan noise problem--this will block airflow to the CPU, which if it wasn't really overheating, will if you do that, possibly damaging it.

    The fan runs fast when the CPU is running hot, or the CPU temperature-sensing diode (Apple Service utilities refer to this as the CPUT diode) thinks it's running too hot (possibly a defective CPUT diode), or something on the logic board that interprets the reading from the CPUT diode mistakenly thinks this reading means the CPU is running hot. The same problem can occur in other Mac models that use temperature-sensing diodes. I recently worked on a G5 tower, whose logic board had died, so I replaced the logic board. I found that the replacement board would misinterpret the reading from the drive bay temperature sensor, and so it would intermittently kick the drive bay fan to a higher speed than necessary, making the G5 very loud. This replacement logic board's firmware was up to date, so that wasn't the problem, and the drive bay temperature sensor was OK. Some people find some of Apple's firmware updates actually CAUSE these fan over-speed problems, while other people find the same firmware update FIXES their fan over-speed problems--the difference is with something else on the logic board that misinterprets the temperature sensor measurements--possibly these boards' PMU (Power Management Unit)/SMU (System Management Unit) circuitry is defective. The only fix for the tower G5 I was working with, was to replace the replacement logic board--after I did this, the drive bay fan ran at a normal speed.

    The iMac I'm currently working on, reports that the CPU is overheating (the iStat widget says it's running at about 65 degrees C), and shuts down the iMac after it's been on for an hour or two. Running the Energy Saver's reduced settings doesn't help, nor did resetting the iMac's SMU, resetting NVRAM (both from the keyboard and Open Firmware), etc. I haven't yet determined if the CPUT diode is defective, but it's rare for these to fail--the problem is almost always a scrambled PMU/SMU, or a bad CPU module (genuinely running too hot), or a logic board misinterpreting the temperature data. But if the CPUT diode is bad, so far I don't think it can be replaced, or at least I haven't yet determined where it is in the CPU module, which normally isn't a part you replace separately--it's bolted to the logic board, and is replaced only by replacing the entire logic board (Apple calls this the midplane, but I'm old-fashioned about calling it by its "normal" name).

    So, if your iMac G5's fan is running too fast, and you've tried all the various reset procedures, you're almost certainly looking at a logic board/midplane replacement. Most iMacs in this condition, won't spin the lower/CPU fan any slower by making any modifications designed to lower the CPU's temperature, since it's the logic board that's at fault, misinterpreting the temperature data. But it's worth a try to see if that helps. From what I recall, one such mod involves drilling holes in the back cover over the CPU module, and installing another fan to cool it, but you can first test if this will help by just removing the back cover and pointing a fan at it while the Mac is running.
     
  18. Daveway macrumors 68040

    Daveway

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    #18
    ^^Thanks for that in-depth analysis there.
    I recently had my logic board replaced an it lowered the amount of fan action but it does still whine.

    Now where can these 3rd party fans be found? I'm willing to give it a shot.
     
  19. johnsawyercjs macrumors member

    johnsawyercjs

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    Feb 27, 2007
    #19
    Place to buy iMac G5 lower (CPU) fans

    Digi-Key (www.digikey.com) has fans with the same Delta part number as is on the label on Apple's fan (BFB0612H) (Digi-Key's part number is 603-1117D), but the picture of the housing, at:

    http://dkc3.digikey.com/PDF/T072/2008-2009.pdf

    ...looks different. I haven't ordered any of these to see if the fan is transferrable to Apple's housing, but I may soon; if I do, I'll report here. Digi-Key sells them for $12.85. Order page for this fan is at:

    http://www.digikey.com/scripts/DkSearch/dksus.dll?KeywordSearch

    If you do a search for Digi-Key's part number on their web site, for some reason it won't come up, so use Delta's part number.

    Companies that may sell the actual Apple fan and its special Apple housing (beware that some may have outrageous prices--check all these companies for the best price):

    www.applepalace.com
    www.dvwarehouse.com
    www.macresq.com
    www.macsupportstore.com
    www.preowned.com

    And, of course, eBay.

    I just spent way too much time trying to quiet a buzzing, rattling iMac G5 ALS 17" CPU fan, by taking it apart and trying to remove a spring below the lower bearing, as someone named David Craig recommends on the Macintouch web site, but I found it impossible to remove the lower bearing and hence the spring under it. I oiled both bearings with a special oil called Bel-Ray, but it didn't help. Next step: buy a fan from Digi-Key and see if I can graft it into Apple's fan housing. If it can't be grafted, next step is to buy a fan from one of the companies above, or maybe from Apple if they have them in stock when I want to order one, and cross my fingers that it's quieter than the one I'm replacing.

    Daveway: the difficulty in removing the CPU fan in the iMac G5s that you've seen, where you had to remove the logic board first, is probably due to the difference between the 17" and the 20" models. The post by Eldorian above shows the removal process for the 17" model. I haven't tried this in a 20" model, but looking at the Apple Service Source instructions, it does say you need to remove the midplane first, which includes the logic board.

    I also just spent way too much time trying other approaches to cool the overheating, noisy iMac G5 17" ALS that contained the fan I mention above, and thus try make the CPU fan run slower and so quieter, but nothing worked. I had an identical model in my shop at the same time, and ran the same applications, web pages, etc., and it didn't overheat or spin its fan too fast--it ran quiet under all the same circumstances. Here are some of the things I tried, which work for some of these Macs, but not most:

    - Reset the SMU (first, of course)

    - Changed the Energy Saver settings between Reduced, Automatic, and High. High just made the CPU hotter and made the fan run too much, not enough extra to compensate for the extra CPU heating. Automatic was the default, where the fan noise problem was audible. Reduced kept the processor cooler a significant amount of the time, but still, doing anything to raise processor usage, even having just Dashboard open, and two Safari windows open, one with a CNN web page with a couple animated ads, and one at the YouTube home page, caused the fan to run too fast, even when the CPU temperature (I used the iStat Pro widget) was reported to be at the threshold level of 148 F, past which the CPU fan starts to rev up above its default of 1500 RPM. The fan in the iMac I was working on, stayed between around 2940 RPM and 3600 RPM with these web pages open.

    - A known-good installation of OS X, from two other startup drives. Some people report reinstalling OS X helps, but it wouldn't have here.

    - Some people report installing a matched RAM pair, but this iMac already had that.

    - Pointing a fan at the rear of the iMac, so that it was cool to the touch--CPU still got too hot.

    - The known-good power supply, and CPU fan, from the other, good iMac I had in the shop.

    - Installing a gasket along the bottom of the CPU fan's opening to prevent it from drawing in warm air from the inside of the Mac--normally there's a gap between the fan housing and the grille along the bottom of the Mac where it pulls in air from the outside world, and some warm air from inside the Mac could get into the fan that way.

    - Moved the hard drive's temperature sensor to sit right on the body of the drive, instead of along the side, on a bracket that wraps around the drive--this had no effect on measured drive temperature. I was hoping it would be seen as hotter, and thus spin up the hard drive fan more, cooling the hard drive a little, and thus the CPU heat sink, which is directly below the hard drive.

    - Replaced parts on the logic board that seem to be the CPU's temperature-sensing devices. The "CPU T-Diode" seems to actually be a chain of three LMV2011 op amps (used for many purposes in electronics, including temperature sensing), near the lower right corner of the logic board, between the lower RAM socket and the heat sink. These are small, 5-legged parts (3 legs on one side, two legs on the other) marked U3601, U3602, and U3603 on the logic board, and marked "A84A" on the parts themselves. National Semiconductor is one manufacturer (maybe the only one). I found these parts by heating various likely parts on the logic board with the tip of a soldering iron, until I heated parts that caused iStat to report that the CPU temperature was rising, and the fan speed rose; when I cooled them with a can of compressed air, the reported CPU temp, and fan speed, dropped quickly. There's another part nearby, under the edge of the heat sink, that uses the same package, marked on the logic board as VR3100, but heating and cooling it didn't produce nearly the effect of cooling the other three parts. It's possible the actual temperature sensor is elsewhere, even in the CPU itself--I think one is inside the CPU, but either Apple isn't using it, or the CPU they used doesn't contain one--and so maybe the current/voltage delivered by this other theoretical sensor passes through the three op amps, and so any heating of these op amps could change the perceived temperature, but these op amps are supposed to be a type that, when in the proper circuit, are relatively immune to temperature change, which makes me think they're in a circuit that turns them into temperature sensors.

    I tried several other things, but nothing helped this Mac. I wondered if installing a cooler-running hard drive might help, but my feel of things from the above work, was that the CPU has a very localized overheating problem, and was simply getting hotter than it should, and nothing would help short of directing air right on top of the heat sink, with the rear cover removed (not too practical for everyday use), or an add-on external fan stuck to the rear cover, at the spot where the CPU fan's air exits (not the slot at the top of the rear cover), pulling more air out of the Mac through holes drilled in the rear cover. I didn't try this, since it's not my Mac. My client may go for it though, but he originally wanted a logic board exchange--I was trying to discourage him from that, since a replacement board might not be any better, since Apple uses the same stock of parts for repairs as they do for manufacturing the complete Mac, and of course a similar percentage of those boards have overheating problems, as are iMac G5s with these problems. I also had a feel from working on this Mac, that some (including this one) may have two or more problems contributing to the CPU fan running too fast too much of the time: besides outright processor overheating, the SMU in some logic boards may misinterpret the data from the temperature sensors; or the delay time (hysterisis) built into the SMU and/or the fan speed control circuit that's supposed to slow down the fan after the CPU has cooled, doesn't always work properly.
     

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