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Original Post: 11/23/2006

Repairing the power supply on my Power Macintosh G4 MDD FW800 dual 1.42 GHz

I've had my G4 since June of 2003, and never had much of a problem with it as far as hardware goes. Like some, I've experienced hard drive crashes and defective memory modules, but other than that, the G4 has been a solid work horse, until recently.

I was preparing some photos for my website when all of a sudden, the computer shut down. I saw dim flashes coming from the back of the computer, some crackling sounds, and started to smell something like burning electronics. I immediately pulled the power cord from the back of the computer.

When I opened the side door of the G4, I tried to smell around to determine the source of the smoke, but had no clue as to where it was coming from. With the door open, I plugged in the power cord and the crackling sound re-appeared and I saw flashes of sparks from the power supply prompting me to unplug the cord again. Great! just great! Now what is this going to cost, and will I be able to find one?

Searching the internet yielded some surprises. They are still available but at a premium. Unlike the PC, each model of Apple's computer has their own proprietary "custom" power supply... @%*#. The PC uses a universal standard brick that will fit into just about every PC on the market. I would have to give the PC a huge plus in this area (and this is coming from a Mac user). The prices I found for the G4 MDD power supply ranges from $100 to $150 (USD) for a refurbished one and $150 to $250 for a new one. You can get a new one for a PC for less that $50. I've never envied a PC user... until now.

Well, since I may be buying a new power supply, I decided to remove the one that's in my G4 and do a little surgery. Instructions for removing and installing the power supply on a Power Mac G4 MDD can be found on Apples website:
...so, I'm not going to go through any details on removing and installing the power supply (it was a pain). Instead, I'm just going to show what happened to my power supply and what I did to repair it. I'm not an electronics expert at this so forgive me if I sound like a newbie.

[Disclaimer] The following photos and details are not instructions on how to repair a G4 MDD power supply. It is only information I'm making available on what I had to go through to repair mine. (Also, the photos were taken out of sequence when I realized that I may have actually repaired this power supply).

The power supply is located at the top.

The hard drive cages (two of them), optical drive cage and CPU fan had to be removed.

The part number is API1PC36 and it is a 360W unit which Apple started using after complaints about noise with the 400W.

I had to use a philips screwdriver with a medium tip to remove five screws. Three are on the top of the cover...

...and two are on the side.

The cover has two hook tabs preventing the removal of the cover.

I had to slide the cover in the direction of the arrow...

...and lift to disengage the cover.

Hook tab and the slot it goes into.

This wire tie that holds the main cables had to be carefully cut. I slightly nicked the cover of one of the wires.

The fans had to be removed (four screws) to allow easier removal of the circuit board.

There are four screws that hold the circuit board in place (three can be seen here) and one for the ground cable.

The fourth screw holding the circuit board was located underneath this yellow thingie which was glued down over the screw.

With the screws removed, I can now try and remove the circuit board from the housing.

Upon removing the circuit board, I noticed a burn area on this once translucent white plastic.

There's the burn area and the corresponding spot on the circuit board.

This was the source of the sparks, or the flashes of light I saw.

A close up view shows the lousy soldering job by whoever assembled this board.

After a little cleaning with a q-tip and a drop of isopropyl alcohol, I performed my own lousy soldering job. I'm not proud of it, but it worked.

I plugged in the circuit board (be very cautious because high voltage is now out in the open) and used a voltmeter to test these two connectors. I got 5 volts.

Since I had the power supply open, I decided to replace the fans with some new ones. Something I had planned to do back in 2003, but never got around to it.

There is nothing wrong with these stock fans...

...but I had these Verax fans, ready to install, since 2003.

And besides, they're brand new.

Removing the fans connectors from the circuit board resulted in breaking one of the locking tabs. Oh well, I decided to break the other one off too.

This photo shows the Verax fan connector in place.

One of the most difficult part of this entire ordeal was installing these new Verax fans. The rubber grommets had to be guided through the corresponding holes in the housing and pulled through. My fear was breaking these grommets. Luckily they did not. Now I had to retrace my steps to install the power supply back in my G4 MDD.

Everything's up and running and seems to be working well now. I saved quite a bit of money by making the decision to explore the interior of the power supply. I had hoped that installing the Verax fans would make the G4 a bit more quiet, but I think the main fan noise is still coming from the CPU fan. Anyway, the most important thing is, I'm getting a few more miles out of my G4.


Gary Kawamura

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