Power Mac G4 MDD Power Supply Replacement

Written By: Chris Green

Comments: 16

Power Mac G4 MDD Power Supply Replacement

Difficulty

Moderate

Steps

Time Required

25 - 45 minutes

Introduction

The Power Mac G4 MDD uses a uniquely shaped 344W or 400W AcBel or Samsung power supply. It has a 24-pin connector (not 24-pin ATX!). The original AcBel power supplies were notoriously loud, earning the Power Mac G4 MDD the nickname "WindTunnel".

Tools

Step 1

The Power Mac G4 MDD: the last, and the fastest G4-based Mac. This computer boasted up to a Dual 1.42GHz PowerPC G4 CPU (though I have a single 1.25GHz).
Two USB 1.1 Ports
Assorted Audio
Video (ADC & DVI)
Networking (RJ-45 Ethernet/56k Modem)
Some later model MDD's (such as the dual 1.42GHz) Have a FireWire 800 Port Here:

Step 2

Unplug the computer.
Unplug the power supply and all external connections from the computer.
Pull on the side lever and lower the side of the case.

Step 3

The hard drive cages are located here.

Step 4

Cage 1
Start by removing this screw.
Remove the ATA-66/ IDE ribbon cable from the motherboard.

Step 5

Now, remove the power connection from the drives.

Step 6

Push this tab down, and pull the cage toward you.
Now, you can set cage 1 aside.

Step 7

Cage 2:
Remove this Phillips screw:
Disconnect this IDE ribbon cable from the logic board.

Step 8

It's likely that there is a cable clip holding the ribbon cable to the case.
To remove it, push the end, and it should pop up.

Step 9

With the ribbon cable clip free, pull this tab towards you, slide the cage up until it hits the platform under the power supply, and pull it away.
Now, set the cage on top of the CPU, and remove the power connectors.

Step 10

Once the cables are free, set the drive cage aside.
To remove the hard drives from the cages, remove the four screws on the sides of the cage that are connected to the drives, then slide the drives out.
The two cages are cross compatible and can be put in either location.
The MDD does not have a 128GB drive limit like older Macs. My MDD has 3 drives (a 400GB Hitatchi Deskstar, 40GB Seagate Barracuda 7200.7, and a 30GB Quantum Fireball LCT).
Note the ID jumpers on the two drive set. One is set to Master, the other to slave. A single drive can be set to Cable Select.

Thanks - excellent tutorial!

Question: If you have a single internal drive, and a connected extrenal drive via firewire or usb, what jumper setting should be set for the internal drive and the external drive? Booting into Mac OS 9 natively (not via Classic) on the internal drive seems to be sensitive to the jumper settings and I’m having issues getting it to work.

LTG Seb - 30/05/18

LTG: The jumper settings on the internal drives make no difference for any external drives. The jumper settings are to distinguish between Master and Slave drives when there are two drives connected to one ATA/IDE ribbon cable. Since the ATA/IDE drive ribbon cables are purely internal to the Mac, they have no connection to any external drives.

johnsawyercjs - 22/01/19

I ran my MDD with 3-750GB IDE HD’s. When they got flakey I replaced them with 2TB SATA drives in the back cage with a cheap SATA to PATA adapter and they formatted out to 1.8TB. I then cloned (CCC) the boot drive to one of the 1.8TB drives. It boots to the new drive and every thing seems to operate like normal. I don’t know how big we can go but we know that a MDD will handle at least 2TB HD’s and I have 5TB in my iMac 15,1

Glenn Stettler - 01/09/18

Glenn: you might get some extra speed from those SATA drives if you install a SATA card into one of the PCI slots (if you can still find one), and connect the drives to it. I ran a couple SATA drives in my MDD this way for years, before the MDD’s power supply burned out.

johnsawyercjs - 22/01/19

This is an amazing blog. This is my computer, I think a 2004 model. I have a question though; I bought a 1 TB 3.5’ SATA WD Black Performance Hard Drive and have 2 weeks to return it. It appears I need a bridge adapter from the old IDE ATA to the newer SATA, will this adapter work? :

https://www.amazon.com/QNINE-Adapter-Dri...

My dilemma: My hard drive is clicking like crazy (freezing) and I use this machine paired to my old Digidesign DigiRack 001 recording system. It’s proprietary and not forward compatible to anything other than OS 10.3.2 and I need to desperately clone this old Toshiba 80g hard drive in order to keep functioning on this version of Protools.

Carlos Branham, Jr. - 29/09/19

Correction: My G4 must not be the MMD version. Doesn’t have all those peripherals in the rear. Wish I could add a photo. I’m thinking it was build in 2003.

Carlos Branham, Jr. - 29/09/19

Step 11

Start removing the optical drive cage by removing its back cover.

Step 12

Now, remove the IDE and power cables from the drives.

Step 13

Remove these two Phillips screws:
Pull the cage away from the front until it is free.
Slide the cage towards you, and out of the Mac.

Step 14

To remove the drive(s) from the cage, remove the two screws on each side of the drive(s), then pull the drive out of the cage.
My MDD has a 3rd party 22X SuperDrive, for burning DVD's in Leopard (Thank You Generic Drive Support!)

Step 15

You may find removing the system fan is unnecessary to remove the power supply cable from behind it, but if you're unfamiliar with how the power supply cable is situated behind the fan, this step is useful in seeing this.
Disconnect the optical drive IDE/ATA-33 cable from the logic board.
Disconnect the system fan 2-wire power cable connector from the logic board.

Step 16

Grab the system fan by its sides and pull it up and out. The system fan is very large and loud, compared to standard sized fans.

Step 17

To remove the power supply connector from the motherboard, push the top end of this clip towards the power supply connector, and pull the connector up and off the motherboard. If the connector seems to be stuck, rock it back and forth a tiny bit to loosen up the connection, then pull up again.

Step 18

Push on these two clips here to release the power cable.
Thread the power cable out of the small hole it comes through, at the far side of the Mac.

Step 19

Remove this Phillips screw:
There may be a small 2.5mm hex (not Torx) screw here on the back of the case, it must be removed if present:

Step 20

Slide the power supply towards the front of the case, and pull it out. It is a little heavy, so don't drop it on the logic board. Disconnect any drive power connectors that you may not have already connected.

Step 21

The power supply has a 24-pin connector with non-standard voltages, so dropping in a 24-pin ATX power supply without modification isn't a great idea.
The power supply connector has a 25V lead to drive Apple ADC displays, so though it is possible to modify an ATX power supply, it won't be able to drive ADC displays, just VGA, or DVI, though the computer will work fine (I've actually tried this).
It also has three 12V/5V rails to drive all six drives (four hard drives, two optical drives) simultaneously. This is the only Macintosh computer other than the Mac Pro to support six drives.

Step 22

This is also the notoriously loud AcBel 400W "Windtunnel" power supply

I had bought my custom bto PM Dual 1.25GHz G4 MDD in 12/03. I used that computer until 2012 (when I ended buying a Mac Mini). In those years the PSU died on me 4 different times. the 1st one was replaced via my AppleCare plan, the 2nd one I had to pay $90 via an ApplePro plan?, the 3rd one was some compatible Samsung PSU that cost me around $200, the 4th one was a modded PSU that a friend did for me. It's been over 10yrs since I attempted to boot up my old PMD125G4. Am Tempted to try and Revive it, but not sure if the PSU would give me trouble.

Luke Rademacher -

Conclusion

To reassemble your device, follow these instructions in reverse order.

Author

Chris Green

Member since: 11/10/09

36876 Reputation

9 comments

Nice overall, but I don't see the point in removing the fans.

jpkjpkjpk -

Agreed, fan removal totally unnecessary.

maccentric -

Thank you. Used the guide to replace the power supply, in my G4 , with one from a dead G4 I had in the garage.

Jim Asherman - 02/05/16

Great guide ... I didn't remove either of the fans and was able to remove Power Supply Unit. Now trying to decide how to get it fixed or to get a rebuilt or ....

Earth Bound Traveler - 12/08/16

Nice instructions and photos. Another set I'd found on line specified a T-10 Torx for case screw connecting the power supply -- wrong, for mine anyway -- 2 mm hex worked for me.

DaR - 12/08/17

DaR: this is usually a 2.5mm hex screw

johnsawyercjs - 22/01/19

If you have a no-power issue, I have successfully repaired the power supply by changing the capacitor near the 5VSB circuit. In my case it was slightly bulged, once removed it was completely non-functional. It is a 10V 1000uF capacitor, I replaced it with a 1000uF 16V capacitor I had unhand. Follow the 5VSB wire (purple wire) to the PCB and check the capacitors near by. Fully functional now.

Scott Gibson - 18/12/17

For Step 19a, is the little red circle missing which shows where the Phillips screw is that is to be removed?

And for Step 19b, are the two little red and orange circles correctly placed? They appear to be placed upon blank metal surfaces where there are no screwholes.

John Beattie - 06/02/20

Great visual tutorial for the power supply replacement on the Mac MDD G4!

GeneP39 -