Skip to content
Thoughtful, detailed coverage of everything Apple for 34 years
and the TidBITS Content Network for Apple professionals

Replacing a Power Mac G4 Power Supply

Back in February, Apple quietly started a program to replace the noisy fans in the Power Mac G4 (Mirrored Drive Doors). For $20 shipping and handling, Apple will ship you a new power supply and fan along with installation instructions. The program runs through 30-Jun-03, so there’s still time to order if you haven’t yet done so.



I received my replacement power supply several weeks ago, but I didn’t find the time to install it in my dual-processor 1 GHz Power Mac G4 until recently. Since installation involves removing numerous cables and drive carriers as well as the actual fan and power supply, I wanted to make sure I could afford some downtime if I screwed something up. Luckily, I didn’t, and I now have a quieter Mac.

Installation Process — Apple’s instructions are detailed and accurate, though the photos are a bit fuzzy. The photos in the PDF version that you can download from the page linked above are higher quality, and you might find it worthwhile to download and print them on a color printer, if available.

The entire installation process took me about an hour. I’m comfortable taking Macs apart, but I was working methodically. An expert repair person could probably do it in 20 minutes; if you’ve never opened a Mac before, it probably makes more sense to pay a dealer to install the new power supply for you.

Overall, the instructions worked well, and I had no significant troubles, although convincing the new power supply to slot into the tabs in the case took several tries. The instructions aren’t kidding about needing a Phillips screwdriver with a magnetized tip; my normal Wiha screwdrivers lack magnetized tips, and removing and reinstalling the screw that secures the back hard drive carrier would have been extremely tricky if I hadn’t found another screwdriver with a magnetized tip.


Speaking of screws, that’s the one place the instructions fall down completely. They do fine at telling you which screws to remove, but they’re silent about when to reinstall those screws until the very end, when they remind you to check that all the screws you removed were in fact reinstalled. As long as you keep the various screws separate, and refer back to the disassembly steps, though, it’s easy to figure out when to replace which screws.

Quieter, Less Powerful — The new power supply is rated at only 360 watts, compared to 400 watts for the original. Apple says that won’t make any difference. Similarly, the new fan appears to have slightly different specs.

More to the point, is it quieter? Yes, though it’s certainly not silent. I looked into buying a sound meter from Radio Shack, but theirs went down only to 50 dB, and I wasn’t sure if that would be low enough. So, lacking a real sound meter, I figured out a different method of testing. My iBook has an built-in microphone, and the Mac OS X Sound preferences pane’s Input tab has an Input level display of 15 "lozenges" that look almost exactly like those answer bubbles you have to fill in with a #2 pencil on standardized test forms.

By maxing out the Input volume setting (thus increasing the sensitivity of the iBook’s internal microphone to the maximum), I was able to determine that the original power supply generally registered 6 lozenges, occasionally dipping to 5. I took that reading right next to the machine; I also took a reading at where my head is normally located several feet from the machine. That second reading registered 5 lozenges, with frequent dips to 4 and occasional dips to 3.

After performing the power supply transplant and turning the Mac on again, I was pleased to note that the noise level was noticeably lower. Performing the same tests with the iBook revealed initial readings of 3 to 4 lozenges right next to the Mac and 2 to 4 lozenges at head level, with 3 lozenges being the most common reading.

There’s no question these results are highly unscientific, since the precision of the Sound preferences pane’s Input level display is sorely lacking. I also wasn’t able to control for the temperature of the room, and since the fans are variable-speed, their noise will undoubtedly change as they increase speed to deal with higher temperatures.

My main complaint is that the new noise of the power supply isn’t entirely even. At a specific fan speed, there’s a slight burbling, and I find that burbling more distracting than the previous noise, which was louder, but even. In an attempt to isolate the burbling, I opened the Power Mac while it was still running (which Apple recommends you don’t do). That messed up the carefully designed airflow, and caused the fans to increase speed – and noise – significantly. I wasn’t able to locate the culprit, and a few minutes after I closed the case, the speed and noise returned to what has seemed like normal so far. After a few weeks, I became more accustomed to the new noises, and the burbling doesn’t bother me as much now.

Worthwhile? If you have a covered Power Mac G4 (Mirrored Drive Doors), should you spend the $20 on the power supply replacement? I’d say yes, since the only downside is the minimal cost and the slight risk of damaging your Mac if you’re careless while disassembling it. If, for whatever reason, you don’t like the sound of the new power supply, you can always reinstall the old one. Although we initially reported that Apple would provide an airbill to return the old power supply and fan, and the program is called an "exchange," I received no such airbill in my package, and there are no instructions about how to return the old power supply in the box. There is, in fact, a single sheet of paper that says, "The parts you have replaced as part of this exchange program should be disposed of in accordance with local laws." If I remember my classical education, trying to figure out your local laws with regard to the disposal of power supplies is in fact one of the labors of Hercules. So I’m keeping my old power supply, just in case; if you feel the need to get rid of yours, try giving it to whatever local computer recycling center you may have.

This Power Mac G4 is still the noisiest thing in my office, and I think it’s still noisier than the 450 MHz Power Mac G4 it replaced, but it’s better than before. Audio and video professionals who need silence will still likely want to isolate the Mac in another room or in a soundproof enclosure. Most everyone else will probably be happy that the new power supply and fan are indeed quieter, even though this replacement won’t eliminate jealousy over the silence of the fan-less Power Mac G4 Cube and older iMacs.

PayBITS: If Adam’s experience convinced you the power supply swap

is worthwhile, why not say thanks with a few bucks via PayPal?


Learn more about PayBITS: <>

Subscribe today so you don’t miss any TidBITS articles!

Every week you’ll get tech tips, in-depth reviews, and insightful news analysis for discerning Apple users. For over 33 years, we’ve published professional, member-supported tech journalism that makes you smarter.

Registration confirmation will be emailed to you.

This site is protected by reCAPTCHA. The Google Privacy Policy and Terms of Service apply.