This model adapter will work for Mirror Drive Door G4s.

Before getting started, I would like to go over the potential drawbacks to using an ATX power supply in these systems.

ADC Power will be disabled. ADC Power is used to provide power to several Apple Cinema Displays. Since the adapted power supply will not be able to provide the 25v required for these displays, you won't be able to use them any longer.

Deep Sleep may not be reliable. Macs require a minimum of 5v during deep sleep, which is deliverable from an ATX power supply. Unfortunately, ATX power supply build quality varies greatly and not all power supplies are capable of supplying this power reliably when the machine switches into or out of deep sleep. If your power supply isn't capable of delivering reliable power, your system may not sleep, or it may experience freezes when waking up. In these cases, it is advised you consider a different power supply or preventing your system from going to sleep.

Using a Firewire Device while having an Apple ROM Maxtor Hard Drive installed in your tower may result in that drive ceasing to function. Details are sketchy on this, my own testing hasn't experienced any problems, but please be aware that this is a potential problem. This has not been reported on MDD systems yet, but since it was reported when using ATX Power Supplies with other G4s, the possibility exists.

I use ATX 20-pin to 24-pin adapter cables to begin my modification to make things easier and to keep the power supply unmodified. I find it extremely difficult to find 24 pin extension cables at a reasonable price, so I don't use them.

Nearly all of the wires in a MDD connector are different from ATX, so it's easiest to remove all of the wires from the motherboard connector and start fresh. Before you start reinserting, you'll want to connect the ATX Power OK (Pin 8, Gray) to one of the 3.3v lines.

You can remove one of the +5v lines and the -5v line from the harness as they're not necessary. If you're using a 20 to 24 pin adapter like I do, you'll want to remove half of the split +5v line and you'll want to cut one of the connections from the split ground line.

Next, I would recommend using a HD power to P4 adapter to add more +12v and ground lines. In my adapters, I like to connect one of the P4's 12v lines to the one already in the 20/24pin adapter to better balance the power draw among the two sources. I also connect a diode at this splice to run a protected line to the 25v connection. This is to provide power to the digital audio circuitry as well as Firewire devices.

This is how my BETA MDD adapter looks:

For convenience, I have started offerring an option to purchase the MDD adapter with an extension to make installation a little easier in some cases. MDD adapter installation is still very difficult to do, so be prepared for a challenge.

Warning:

The tricky part of MDD Adapters is installation. There are a lot of sharp metallic edges in a MDD case, especially near the connection to the motherboard, so you need to be VERY careful when installing. It is extremely easy for a wire to be cut, short out, and cause irreparable damage to the motherboard, CPU, or power supply.

I realize most people use MDDs with all the hard drive bays filled, but I would highly recommend removing the front drive cage when using the adapter.

It is also recommended that you use an ATX power supply with a long motherboard harness to make it easier to route cables. Please, try to use the same wiring route as the stock power supply to help avoid sharp edges and pinching the wires. It is also recommended that after you have the adapter installed, you try to wrap it in electrical tape or other plastic to help protect it.

I have a limited number "BETA" adapters available for sale and am working to create a better solution for future adapters. Future adapters will be longer and may include heatshrink or other protection for the wires that will be similar to that of the stock wiring harness. These adapters will be more expensive due to extra cost of parts and extra time to mold the wires into shape, but should provide a better overall experience. *Update* Beta Adapters are SOLD OUT

At the moment, there is no real guide for how to install an ATX Power Supply in a MDD G4. It is tricky as the original power supply is not a standard size. You'll likely want to position it above the optical bay. If you place the power supply here, you will need to raise it high enough for the video card to slide under it when the door is closed. You will also need to pay attention to where the AC power cord connects as it will need to be connected before closing the case.