Mac Minipowermac G4 Cuberepair


(the issues regarding these powermacs and the power supply failure is prevalent and much discussion has been made regarding replacing the PSU with a new one or modding an ATX power supply)

Hello, I just want to share my experiences and solution with fixing my MDD PowerMac power supply.

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Mac Minipowermac G4 Cuberepair

First some quick background:

A few years back my Mac would reset its clock back to December 31, 1969.

And at times it would not power-up unless I switched off/on the power switch on the power strip or unplug/plug the power cable.

I replaced the PRAM battery and reset the PMU.

The problem was intermittent and though it was slightly inconvenient I was able to deal with manually updating the date/time settings, etc.

Mac G4 Cube

A few weeks ago, I decided to give the inside of my Mac a quick spring cleaning.

When I tried to turn it back on, it was completely unresponsive.

Since I knew the PSU, was prone to catastrophe I decided to open it up and take a peek.

But first a disclaimer:

I am not an expert in electrical engineering so my 'solution' may not (or it may) work for your particular case. Additionally I simply stumbled upon this quick solution while I was 'poking' around.

When you open up the PSU you should see something that looks like a cathode terminal, a few inches from this is a heat sink. If you happen to accidently touch both pieces at the same time you will receive a nice buzz. That is because the PSU and its capacitors/inductors have electrical charge stored in them.

What I did was simply arc the two pieces of metal using a thick screw driver with a rubber grip. This short circuit will simply discharge the PSU and you will see a spark or two as the electrical current finds the ground. (it also leaves a nice little nick on the shaft of you screw driver)

(That whole last part maybe a bit unneccessary, but it sure is fun to do and it brings back memories of how we use to 'hotwire' our HMMWVs)


After checking with a multimeter, I verified that the PSU was getting the correct input voltage.

My next logical step was to check output voltage.

Since I didn't know what to look for in the PSU, I closed it back up.

(I should mention that there were no signs of burnt or exploded circuits, diodes, capacitors etc. and that I could not locate a standard fuse.. it turns out the fuse is a built-in 250 V - 8 amp ceramic fuse and proximal to where the power cord enters the PSU)

The next step was to test the output voltage, so I figured I'll check it at the terminal where it connects to the logic board.

I googled the pin out and then I checked the voltage.

Since I was getting the right voltages I put everything back together and then.. VOILA.

The Power Mac G4 Cube

My Mac powered on flawlessly, even the date and time settings were preserved.

Hopefully this it will work for others. I am not sure why it worked, but it did after I was unable to power-up my Mac.

With this quick solution I was able to bring my Mac back to life three times using that last trick.

What I simply did was measure the voltage with a multimeter between, if I recall correctly, were Pins 11 and 12.

Power Mac G4 Cube Teardown

Car rental landing page free download windows 10. Try that combination: between Power On and Ground or between the +25 V Standby and Ground.

Apple Power Mac G4 Cube

Thanks for reading. Hopefully this helps out. Let us know if it does.

PowerPC Lives!


MDD Dual 1.42 GHz PowerPC G4, Mac OS X (10.5.8)

Posted on Jun 17, 2013 12:24 PM