iMac G5 overheating(?) issue

Don't pull your hair out, replace your power supply unit or make sure that your thermal cables are properly routed and that your thermal paste hasn't dried out. 178º is too warm, 150º should be the max. You might have Apple lubricate the fans, and also, you can vacuum your air vents, which might be clogged with dust. Since you have an iSight, you void the warranty by opening it, and anyway, it's not easy.

I'd rather vacuum than blow dust into the machine, and unfortunately, yes, Apple will probably charge. If you're brave, you can open the machine, see instructions here:


http://www.kodawarisan.com/imacintel/imacintel01.html
http://xlr8yourmac.com/systems/imacisight_internals/imac_g5_isightinside.html
http://nl.youtube.com/watch?v=iVgL9u7ySUk
http://nl.youtube.com/watch?v=fI_QmBueWg4&feature=related


Let us know how you make out,

I have a "non iSight" version iMac G5 (flat screen) that began acting up after about two and a half years after I bought it. While the unit was still under Apple Care coverage, the Apple Store unsuccessfully worked on it twice, then they sent an Apple tech to my house. I don't know exactly what the store techs did, but at my home the tech changed out the "logic board" (AKA, the motherboard). Unfortunately, none of the three attempts by Apple addressed the problem(s), which I began to believe, and now firmly believe to be related to CPU overheating. Apple refused to further address the problem once the Apple Care "contract" ended, although it was clear to me that none of their three previous attempts had been successful. So, the problem was mine to either address myself, or go broke paying for Apple again and again. After reading many many blogs and on-line complaints about iMac G5 overheating, I installed the "Temperature Monitor" software application, and confirmed that both the CPU temp and, to a lesser extent, the HD temp were both frequently being driven above manufacturer's operating temp specs, appearing to cause the CPU to act sluggish and to eventually shut down. Eventually, after reading a lot of complaints and theories about the problem and its solution, I took the unit completely apart, cleaned out all dust and dirt, cleaned off old thermal grease, and very carefully applied new thermal grease, but __the problem still remains__. Fans spin up as the temp rises, but they simply do not seem to have the capability to keep the temp from pegging above spec. I have learned to keep my eyes on the temp, then simply shut down streaming apps and tread lightly to keep the temps "below redline". One thing that really surprised me when I had the unit in pieces was the fact that the CPU's heat sink appeared to simply be a large thick piece of copper sheet mounted UNDER the motherboard (connected via thermal grease), whereas the graphics chip and a second large chip were attached via thermal grease to the large finned heat sink that is mounted ABOVE the motherboard, and which is cooled by air that is ported through large fins. (When you remove the iMac's plastic cover to expose the interior of the unit, the heat sink bears a large "G5" marking on a thin sheet metal cover.) Since the large copper sheet that appears to heat sink the CPU doesn't appear to have air flow ported across it, nor does it have fins to throw off heat, it seems to me THAT might be a heat control design issue. My CPU temp runs at about 154F at idle, and it rises to the mid 160s when surfing the web (which is not a particularly big stressor of the CPU, but, nevertheless, the CPU temp almost immediately rises at least 10 degrees F when I begin surfing the web. I can easily drive it to the high 170s (F) by opening an audio stream while surfing, and, given time, the CPU temp rises to the max temp spec of the G5 chip (the mid 180s). Eventually, if not addressed by shutting down apps, the CPU will shut down. So, I have grown to put up with all this, but I am really really disappointed that I have NOT been able to figure out a solution, nor has Apple or any of the web sites I have visited given me any additional ideas (that have worked). When I bought the iMac G5 I do not recall having any of the surprise shutdown issues, or the "spinning wheel" problems that led me to my first visit to the Apple store to begin addressing this problem. Dirt and/or air flow are NOT the problem, nor is the problem due to stalled fans. All of them are turning (although I do hear them running now, which is something I do not recall occurring when I bought the unit). As for dirt or dust hampering air flow.... you could eat off the inside of my iMac. Please, if you have any fresh ideas that I can try, I would appreciate hearing them.

First, welcome to Discussions - you seem to have covered things thoroughly, the only thing I can think of is to train an external fan on the back of the machine to keep it cool. I realize this is a kludge, but it often works.


The other thing you can do is call Apple Customer Relations at 800-767-2775 and tell them what has been going on. They will, perhaps, be able to hep you.


Let us know how things turn out please,

Miriam, thanks for suggesting a call to Apple Customer Relations. I'll try that. As for aiming a fan at the rear of the computer (or cutting a hole in the rear and attaching a muffin fan - the latter of which is one solution that I saw on the web), neither of those two suggestions are really solutions as far as I am concerned. I do have a newer iMac, a Mac Mini, and a MacBook as well as the older iMac G5, the latter of which is the unit that has given me the troubles I described. So, I can probably live without the older iMac, but it still has a lot of life left in it, so I just want to fix it. At this point I regard getting this problem fixed "the right way" as sort of a personal challenge. With all the complaints I've seen on the INTERNET describing what is clearly a thermal problem with the iMac G5 I would have thought that by now Apple would have published a fix, although I can also understand that the company may be afraid that customers of this now aging product could become very angry if they conclude that the problem could have been a design deficiency. After battling the "Microsoft Blue Screen of Death", and their endless patches for years, I have become a staunch Apple supporter, so I just want to fix this problem and move on. Before I make that call, there is ONE idea that I want to throw out to you: One thing that a lot of folks complain about relative to this problem is fan noise. Clearly the fans spin up and are part of a feedback loop to control CPU and HD temp. But, prior to having this problem I NEVER really HEARD the fans. Now the fan noise is clearly well above the very low hum level I heard when the unit was new, and that was comparable to the very low fan noise I hear in my newer INTEL version iMac. This is a long shot, but could one of the fans have developed bearing friction that may be reducing its capacity to move as large a volume of air as it had when new ? (I am thinking primarily of the fan that is located in at the bottom of the chassis, just adjacent to one of the speakers. It's the one that blows across the fins under that G5 logo that cools the two chips I described earlier). This is about the ONLY remaining idea that I have relative to this problem. Just soliciting any feedback on this idea? I'll certainly call the 800 number you provided, and thank you very very much, Miriam, for your very quick response.

An ingenious thought, but unlikely. In almost all the cases I know of when the fans become noisy, it signals the impending failure of the power supply unit or another thermal problem, like dried thermal paste. The bearings could need lubrication, but I doubt it. You might like to try doing this yourself, since your machine is well out of warranty. If you succeed in solving your problem, please post back and let me know.

One problem I had for our iMac G5 . . . the fans running (even after cleaning / vacuuming dust out). OSX 10.5.7 seems to have ramped the fans up . . . as I'd experienced with an iBook, and later updates in 10.4 . . . things running hotter after new updates . . .

My "Lucky" Solution: I forgot that I'd recently changed the "Sleep after 15 mins." setting to "Never" (probably because I wanted some big update / download done right, ha ha) . . .

Wehew, that was an easy fix, and "fyi" . . . just changing it back and it's back to normal . . . vs. it being "on" all day.

HTH,
:] JB

ps There's also an option to change your processor to "Reduced" which may help . . .

pps Our HD was pretty full (last 3 GB) and I offloaded lots of music & photos (82 GB) to two separate firewire drives. I think the machine was needing to work extra when the HD was almost full.

For what its worth.......

I have an iMac 17" 2GHz ALS here on the bench that is regularly getting into thermal runaway and shutting itself down.

The owner is fed up with it, has bought a new machine and left it here as 'junk' - so I'm at liberty to experiment with it...... : )

Facts:

* Mini-heat wave at present so ambient temp is 30'C
* iMac G5 idling at 76'C ( from Temperature Monitor sw), fans on hard, but not reducing temp
* Modest browse on net - temp goes to 89/90'C within 5 mins - self shut down.
* Take machine apart (not very dirty) blow out ALL traces of dust / fluff
* Re-assemble - no different
* Take apart - examine carefully - NO bloated or leaky capacitors on MLB or in PSU.
* Dismantle machine and CAREFULLY re-seat CPU sink with new paste-no different.
* Take apart re-re-seat heat sink ULTRA carefully with new compound - still no different.
* Run machine with Service diagnostics - no faults found

Q:- WHY can't the heatsink dissipate the heat???

Remove heatsink
Remove G5 shroud and cover to expose fins ( all in bare copper finish) -Why not black?
Clean heat sink and spray upper surfaces / fins matt black
Re-assemble machine with heatsink but with no cover or duct - i.e. exposed fins
ALL other components (fans etc) in place.
ReStart Machine and let idle for 30 mins.......

CPU temp now 62/63 'C rising to 71'c when playing a DVD at 3/4 screen size.... no shut downs.

Fans on quite hard but holding at present at 71'C (with ambient at 29'C) after an hour.

Its not hard to see why Apple have the heatsink design the way they do (ducted air) but it really doesn't seem to work very well in practice.....

Also, since when was the best finish for a heatsink bright metal? I was taught that matt black is the best colour for radiating heat?

Anyway, - pause the DVD and the temp drops to 64'C within 30 secs and the fans also quickly drop back to a fast idle. Also, the CPU temp readout reacts MUCH faster to fan changes without the heatsink duct in place than with it.

Finally, given that there is very little in the way of natural venting on the back cover, it begs the question as to how well the modified (now black) heatsink would work with some additional holes in its vicinity? I've got a spare back-plate / stand in the workshop so that's the next experiment!

Will report back when I've tried it, but for now I at least have a WORKING 2GHz iMacG5 running in a fairly warm environment and that doesn't go into forced-sleep every 5 or 10 mins.

(Energy saver option for CPU was /is set to automatic - putting it on 'Reduced' made a small but noticeable difference of about 1.5 to 2'C )

John Hill

Disclaimer: This machine was 'given' to me so experimenting with it involves no risk / loss (to me). The modification above is definitely not in the approved Apple handbook!
Carrying out the mod involves extensive dismantling of the machine and shouldn't be considered if you are not experienced or confident in doing this sort of work nor have appropriate facilities (static etc).

Update on post above.........

Drilled backplate with 15 x 7 mm holes in a 3 x 5 grid positioned to be centre on, and at top end of the CPU heatsink when backplate fitted -( but just below the grey exit duct ).......

Results:

Idle temp down by 1.5 'C

Running temp (DVD playing at 3/4 screen) down by about 2.5 to 3'C -actual 68.3'C,

( original - before heatsink and case mods was around 86'C rising to 90'C and shut down)

In addition, HDD temp = 46'C throughout (which I still consider a bit warm)

Food for thought?

John H

Good information, but I'm afraid it's way beyond the general tech skills of most posters. I would be loth to disembowel my iMac the way you have done and I suspect that, other than confirmed tinkerers, most posters here would feel the same.

@MGW

I would agree with you on this and I'm not trying to encourage the average user to 'disembowel' their Mac in an attempt to resolve this perennial overheating problem.

For some more 'techy' types at the end of their tether with a similar machine I thought the results of the experiment might be of some value / save them some experimenting.

Further to my earlier posts, I now wouldn't encourage users to cut holes in the rear panel... it does help by virtue of a few degrees but is never going to look 'pretty' or tidy unless the user has some decent workshop equipment to achieve a neat job. There may also be an issue with altering the machine's EMI shielding as well ?

I have now found that removing the heatsink's shroud - trimming it to leave the first 2" ( i.e. the end that abuts the fan ) and replacing this very cut down version, achieves a similar effect to cutting holes in the case.

This is probably due to it ducting all the available air from the bottom fan over the first 2" of the heatsink (which is where the CPU is), but then allowing the rest of the (now black) heatsink to radiate more freely. I also removed the grey exit duct at the top of the 'sink' to allow waste air to exit the case more freely.

Machine's CPU now idles at almost exactly 38'C above ambient (Currently 27.0'C) and fans aren't running 'hard' all of the time....... which means its usable again.

This does beg the question as to why some of these machines have CPUs that seem to live permanently on the 'thermal ragged edge'....... perhaps its something to do with the cpu production process and luck-of-the-draw as to how good a 'chip' your machine has?

As said in my 1st post - this definitely isn't an Apple approved approach - it does seem to have improved matters significantly (dropped CPU idle temp by about 10'C), but this machine was given to me to 'play' with, so has cost me nothing but my time.

Don't try this if you can't afford the risk of damaging the machine!

Regards

John Hill

This interests me as I too have a 'spare' iMac after buying a new one because I was told the old G5 would cost £400 to repair, as it needed a new logic board - the fans are on full all the time.

I'm not convinced the unit is overheating, though, but rather that the fans are not being properly controlled.

I'd like to get the computer working as it's only worth £50 on eBay. Does anyone know of a cheap fix? I don't mind pulling the machine to pieces...

thanks

Phil

Hi,
_*Disclaimer this is what I did, if you don't understand the dangers of electricity or boiling water then don't do it YOU COULD DIE OR DAMAGE YOUR COMPUTER!!*_

just in case someone ends up here as I did for overheating on a 2.1ghz isight g5.
My problem was overheating especially with cpu activity of 100%. In my case the problem was cured by changing the cpu heatsink I'm guessing the heatpipe failed.


I found the following checks suggested this was the problem both involve dismantling,



1)
!!DANGEROUS
I removed the screen and used the mini vga adaptor to an external monitor
Checking the temperature of the cpu fin section I found that by comparison with gpu fin section it was cool.

2) I dismantled the imac remove the cpu heatsink put the cpu end of heatsink in boiling water and the other end did not get hot


The problem with the above is apple don't sell the heatsink seperately so you will need to find one elsewhere, makes me wonder just how many logic boards where replaced for this reason.