iMac G5 power supply burnout: New (Ambient Light Sensor) models less affected

We've covered a number of issues with iMac G5s apparently overheating, and generating excessive fan noise in an apparent effort to cope with the heat. In some cases, the overheating can cause actual component damage, causing the power supply and other parts to fail.

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.

One MacFixIt reader writes:

"I'm an Apple Certified Technician, works on a Apple Authorized Service Provider and seen a lot of iMac G5s with blown power supplies and motherboards with a simple variation of voltage. Some clients complain about turning off their iMacs G5 after some work and when turning it on the machine shows smoke all over their desk.

"After opening a problematic iMac G5 (almost every one that comes into our shop) and checking the power supply, we can see some blown capacitors and also the power supply.

"Today I received 3 machines with the same problems."

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.

To recap, 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.

We recently posted information regarding a potential home-made fix being offered by a MacFixIt reader that purportedly lowers the operating temperature of the iMac G5 by several degrees Fahrenheit. However, there is no guarantee that this fix will prevent the iMac G5 power supply from overheating, and will likely void your Apple warranty.

If you are experiencing a power supply burnout issue with a June 2005 (Ambient Light Sensor, or revision B) iMac G5 or have other feedback, please drop us a line at late-breakers@macfixit.com.

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