iMac G5: Power Supply Burnout/Component failure due to overheating

CNET staff

Sept. 2, 2009 11:53 a.m. PT

5 min read

Some iMac G5s exhibit an issue where specific components of the system overheat and -- in some instances -- melt or otherwise suffer physical damage. The issue appears to be relatively widespread, with a large number of users now reporting the issue.

As noted yesterday, users experiencing these problems generally must replace one of two hardware components: the power supply, or the "mid-plane" assembly which consists of the motherboard and other circuitry. In most cases, users whose machines are still under warranty or AppleCare are able to quickly obtain replacement parts that resolve the issue.

Problem limited to models produced during a specific time-frame? Speculation holds that this issue may be relegated to iMac G5s produced during a certain time frame -- specifically the last month or two of 2004.

One reader, who works for an Apple authorized service provider and wishes to remain anonymous, writes:

"All of the iMacs that have had this problem when I process the warranty information with Apple have an estimated purchase date of December. I had not seen any imac with a power supply problem before the first of the year. I understand that this may be anecdotal but so far this is the only link I have found on these machines. I suspect a bad run of parts from the supplier which could also explain why they disappeared in availability as service parts and why the imacs we have ordered for our sales floor are not shipping.

Precursors to burning: Sudden shutdowns, FireWire problems There are a number of symptoms for this issue that can occur before the more serious burning of components manifests.

First, many users notice that their iMac G5s begin to spontaneously shut down -- typically during periods of heavy processor/disk activity -- before more serious issues become apparent.

Second, some users notice that their iMac G5s are unable to recognize FireWire devices before complete unit failure.

MacFixIt reader Gerrit DeWitt writes:

"I'd like to substantiate your reports of the electrical 'burning' smell with another interesting detail - inability to recognize FireWire devices before unit failed:

"Brand new iMac G5 20-inch:I immediately noticed a faint, electrically charged 'ozone' smell, which I did not initially recognize as coming from the iMac. I got as far as the "do you already have a Mac" step in the Setup Assistant when I noticed that the previous Power Mac G4, placed in target disk mode, was not recognized. I called Apple and tried various scenarios of plugging the G4 in before booting the iMac, when the Assistant launched, etc., with a support agent on the phone. When I unplugged the FireWire cable from the iMac and plugged it into the unit's other FireWire port, the unit powered off. Only after opening it and performing a PMU reset did the computer restart.

"We tried one last time, skipping the 'previous Mac' step in the Assistant and creating a local account. Still, the Power Mac G4's hard disk wouldn't mount via Target Disk Mode. Upon switching FireWire ports on the iMac, the same thing happened, this time accompanied by a very strong burning smell. I unplugged the unit and sent it back to Apple.

"About six weeks have passed with no replacement unit or status update.

"For reference: The FireWire cable was new and in working condition, and the Power Mac G4 was able to successfully enter Target Disk Mode. Other computers could mount it correctly in that way."

Who is manufacturing the defective power supplies? We've also received speculation from several sources on why defective power supplies are making their way into shipping systems.

A reader who also wishes to remain anonymous writes:

"An acquaintance had a similar problem and went through two mid-plane assemblies and power supplies within two months. Candidly, one of the technicians stated that two of Apple's three power supply suppliers manufactured potentially defective parts.

"There likely exists bad circuits in the power supplies from two of the manufacturers that fails to 'crowbar' or shut down when they reach a particular amperage. This in turn causes the mid-plane assembly to overload and fail.

"Based on the technician's statement and the fact that Apple has detailed and automated mid-plane assembly trouble-shooting instructions in its support section, Apple internally knows about this problem but, to my knowledge, has made no formal public announcements regarding the defective power supplies.

"From the acquaintance's experiences and the fact that only the last technician knew the details of the manufacturing problem, it appears that Apple intended to install the potentially defective power supplies until they are no longer in stock, as the problem manifested itself only upon the running applications that demanded 100% of the machine's processing power for a sustained period.

"After a bit of stonewalling from Apple, the acquaintance got a new machine."

New models not affected as often It appears that this problem afflicts more first generation (rev A) iMac G5s than later (rev B, or Ambient Light Sensor) models. The later, less susceptible models include the iMac G5 20" running at 2 GHz and other models sold from June 2005 onward.

Potential home-made fix for iMac overheating MacFixIt reader Tim Martin has developed a potential fix that purportedly significantly lowers temperature, but will likely void your Apple warranty and is not guaranteed to stop the power supply failure problem:

Tim writes:

"Due to overheating issues with my own iMac G5 17" 2ghz machine, I am developing a fan mod that may have commercial merit. Installing this involves precision cuts with a hole saw best performed on a drill press here, to a users' own back panel. CPU temperature is lower by 20-25 degrees F. This could be offered for US $199 and return shipping costs, I am near Phoenix."

If you are interested in the fix, you can e-mail Tim at ehometech@earthlink.net for more information.

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