One of the first things you'll notice about the G4 chassis is that it only has four slot panels in the back. Unfortunately, this means that we can't use a regular ATX motherboard. Not only would the board be too long, but also three of the slots would be inaccessible. With this in mind, we had to pick a motherboard that would be able to fit in the chassis.
The AOpen MX3L
The motherboard view - Socket 370, 440LX, AGP and three PCI
Yes, it's a rather outdated motherboard, but it came cheaply and I didn't have to buy a new processor or memory for the system. The motherboard will be accompanied by a Celeron 466MHz and a Mushkin PC133 Enhanced 128MB v2.
One of the peculiar things about this motherboard is the location of the floppy cable connector - of all places for it to be, it's on the side of the processor socket! Well, since I've got a bootable CD-ROM drive, I won't really need the floppy anyway. Still, I'll be using one, so it's something I'll need to negotiate with.
The G4 I/O shield
Here's where we can find one of the major complications of this project. The G4 I/O shield is significantly different from the standard ATX I/O shields. Of even more concern is that they're not the same size, which means that I'll need to figure out how to make them compatible.
My original plan was to cut a rectangular-sized hole in the G4 shield, and then attach the ATX shield to it. In order to do this, however, I had to break off a tab from the G4 shield which was preventing the motherboard from seating flat. Sorry about the blurry picture, but you should be able to see the place where the tab was broken off.
Sizing up the situation
In order to take sizings on the I/O shield, I needed to know exactly where the motherboard is going to sit. To do this, I put in the video card and an ISA card, and attached them to the PCI slot panels. Since this is the most important thing to line up in the chassis, we can use this as the origin to measure out modifications elsewhere in the chassis.
Something else that the careful eye will notice about the ATX ports on the motherboard is that they don't line up exactly with the opening in the G4. However, the most inconvenience this will cause is the inability to use older joysticks and the microphone jack for the onboard sound. Since I was planning to use a separate sound card anyway, this is really trivial. To make the joystick port fit, I had to use a hex-driver to remove the right-hand screw-bolt. This puts us back on track.
Our "modified" Sharpie
The standoffs in the G4 case weren't anywhere close to where they needed to be for the ATX motherboard, so we needed to put in holes for the new mounts. Without a good pencil or anything, we took apart this Sharpie marker, pulled out the inking tip, shaved it down some, and put it back in where it could reach through the mounting holes to mark on the motherboard tray.
Marking the holes
Here's a shot of myself actually marking the holes. If you look up in the upper right-hand corner, you can also see the EMF trap that normally goes on the back of the G4 shield. Apple puts this stuff all over the seams and linings of the case to help keep EMF from getting out of the case, as well as outside EMF from getting in. I've only seen one other chassis that had this stuff installed, so it's another option that Apple went with to make the Macintosh chassis even sweeter.
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