The Power Mac G4 MDD Used a uniquely shaped 344W or 400W AcBel or Samsung Power Supply. It had a 24-Pin Connector (not 24-Pin ATX!) and the original AcBel power supplies were notoriously loud, and earned the Power Mac G4 MDD the nickname "WindTunnel," since the computers were so loud.


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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).
  • 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).

  • Six USB ports.

  • Four FireWire ports.

  • Assorted SCSI (SCSI50/SCSI68)

  • 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:

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Pull on the side lever and lower the side of the case.
  • Pull on the side lever and lower the side of the case.

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  • The hard drive cages are located here.

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  • Cage 1

  • Start by removing this screw.

  • Remove the IDE ribbon cable from the motherboard.

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  • Now, remove the power connecton from the drives.

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  • Now, push this tab down, and pull the cage towared you.

  • Now, you can set cage 1 aside.

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  • Cage 2:

  • Remove this Phillips screw:

  • Disconnect this IDE ribbon cable from the logic board.

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  • 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.

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  • With the clip free, pull on this tab, lift the cage up, until it clicks, and pull it away.

  • Now, set the cage on top of the CPU, and remove the power connectors.

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  • 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, than slide the drives out.

  • The two cages are cross compatible and can be put in either rack.

  • The MDD does not have a 128GB drive limit like older macs, My MDD has 3 Drives (A 400GB Hitatchi Deskstar, 40GB Seagate Baracuda 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 - Réponse

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 - Réponse

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

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  • Now, remove the IDE and power cables.

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  • Remove these two Phillips screws:

  • Now, pull the cage away from the front until it is free.

  • Now, lift the cage out.

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  • To remove the drive from the cage, remove the four screws on the side of the drive, and 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!)

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  • Optical Fan:

  • Remove these two Phillips screws:

  • Now, slide the plate towards the case, and lift it up, and off.

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  • Once the cover is removed, disconnect the power cable and thread it under the dust shield.

  • Now, lift the fan straight up and out.

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  • System Fan:

  • Disconnect the optical drive IDE cable from the logic board.

  • Now, remove the system fan cable.

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  • Now, grab the system fan by the sides and pull it up, it should come free, the system fan is very large and loud, compared to standard sized fans.

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  • To remove the power supply connector from the motherboard, push at the top of this clip, and pull the connector off.

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  • Push on these two clips here to release the power cable.

  • Now, thread the power cable out of the small hole it comes through.

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  • Remove this Phillips screw:

  • There may be a small hex screw here on the back of the case, it must be removed if present:

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  • Now, 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.

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  • 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 then the Mac Pro to support six drives.

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

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

34 autre(s) ont terminé cette réparation.

Chris Green

Membre depuis le 11/10/2009

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Master Techs Membre de l'équipe Master Techs


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

jpkjpkjpk - Réponse

Agreed, fan removal totally unnecessary.

maccentric - Réponse

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 - Réponse

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 - Réponse

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 - Réponse

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 - Réponse

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