Firstly I must thank efion for this Information that gave me direction-

http://efeion.blogspot.com/2007/12/power-supply-fun-part-2.html

some more info here I suggest to read prior to installation-

http://www.xlr8yourmac.com/tips/MDD_ps_mods/MDD_PS_Mods.html

file:///Updates-Downloads/G4%20Power%20Supply%20install/PS%20read.php.html

I have succesfully fitted this Antec Slimline MT 350 watt 24pin ATX power supply to my "Old Faithful" G4 MDD 1.25.

http://www.anandtech.com/GalleryImage.aspx?id=4140

pic sequence below of install..

I VERY STRONGLY ADVISE THAT IF YOU HAVE "NO EXPERIENCE" OR TOOLS TO CARRY THIS OUT,  DO NOT ATTEMPT IT. HAVE A TECHNICIAN DO IT FOR YOU.

This ATX Power supply can be obtained just about anywhere, at well below than that of  a secondhand Mac Power Supply.

Firstly remove the "Blown" Mac Power supply, there are instructions on the web to achieve this.

Then,

Mark out the Case area that requires removal, remove the G4's outer plastic cover then cut the casing to accomodate the PS.

The ATX PS will fit snugly into the area, and will allow the Display card to clear easily when the case is closed.

Fit the ATX PS into the case in the location make sure there are no sharp edges that may damage the PS.

 

 

 

The G4's outer plastic case cover Lug must be trimmed as pictured, to allow for easy fitting to the top left just above the PS casing.

 

 

With a hole saw mark and drill an Air Vent hole in the plastice cover.

 

 

 

 

the completed fittment with the ATX Slimline Power Supply installed.

 

the Vent hole is the Air intake for the Power Supply, the fan will rotate so to "Pull" fresh cool air into the PS.

 

A simple small 90 degree bracket must be fitted as above to secure the PS into place, a piece of the rear casing can be used to make this bracket..

then it's just a matter of severing the OLD Mac power supply cables as close as possible to the Mac PS , and also sever the ATX 24 pin connector from  the cables, we used two simple screw joint cable connectors to join the cables together,

IMPORTANT, the colour coded cables must be connected as per the diagrams below. Also Tripple check that you have connected the cables so the voltages in and out are identical.

 

The Completed Mounted "slimline Antec 350Watt ATX PS in a G4 MDD Mac Dual 1.25.

You will not have the "white 25V" cable to supply power to an apple display.

Apple don't use the POK Power ok line, so it's suggested to connect this into a 3.3v line from the ATX PS.

there are two Molex HDD connectors on the Antec that can be used to connect your System HDD and the optical drive, should you require more just add a line form the old mac PS to the ATX cables, or use plug-in adapters.

24pin ATX Connectors and Mac MDD PS diagrams below....

IMPORTANT,  READ AS MUCH INFORMATION AS POSSIBLE PRIOR TO ANY MODIFICATIONS WITH YOUR COMPUTER OR ELECTRICAL EQUIPMENT, AND IF THERE'S ANY DOUBT, DON'T DO IT, OR HAVE IT DONE BY A QUALIFIED TECHNICIAN.