iMac in Flex ATX Case
Last Updated: 11-14-04

Assembly

1. The Beginning

I started out this project because I acquired an iMac rev/D from esworp in the #Macosx channel on Undernet IRC. He said the monitor was dead, but the machine itself still worked ok. So soon as it arrived I tried booting it up just for the heck of it with no luck, would turn on and the power light would stay orange. So I popped open the case and hooked up a Mac-to-VGA adapter to a monitor I had. This time it did want to boot, lacking an internal hard drive I stuck in an OS9 boot CD. It then booted and ran fine.


2. The Tear Down

Now was the time to tear the iMac down and get anything and everything that was usable. The main thing needed was basically everything in the boat assembly (boat being manufacturing lingo for the piece of metal that held the mainboard and other components). I set this aside as I already knew I would need most everything from it. The iMac uses a special power plug-in, and knowing I would be adapting this to run off an ATX supply, I pulled the power supply board, and the main power cable going from the power supply board to the power filter module that plugs into the iMac mainboard. I also removed the speakers, mic, headphone port/power switch board, CDROM (not used in this conversion but nice to have around), main cooling fan, and some wire I thought might be handy. I also removed the shielding, which was used around the back of the tube, as it will come in handy later. One thing I would like to point out while taking all of this out, when working in and around a picture tube use EXTREME care. Even though the power is unplugged, the tube can hold a charge of several thousand volts, which can and will shock you if you go poking around.


3. The Layout

Mounting the iMac board turned out to be more difficult then I had originally expected. The rev/A-D iMac's used a power filter board that plugged into the underside of the mainboard. I had originally wanted to run a ribbon cable from this to the filter board, and have the filter board mounted remotely. This would allow me to have the CPU face outwards, making it easier to work on, as well as easier to cool. But after doing some research I felt the ribbon cable wouldn't be up to the wattage that would be going through it. So I decided to mount the board backwards. Which in the end turned out better I think, as the CDRW gets fairly warm when burning. Had the board been mounted with the CPU facing out, it would have been very close to the CDRW, to close to be able to fit a fan. And even if I could mount a fan, it would suck the hot air off the CDRW right onto the CPU. So backwards the board went. I am using stand-offs to make it sit about 2" off the rear panel of the case. This put the rear ports in just about the perfect position to allow me to use the original iMac port cover.


4. The Power Supply

The main thing that sets an iMac conversion aside from a G3 or G4 tower conversion is how to power it. Many people go around the problem by using the original power supply. While this works, the original supply was designed to power not only the iMac mainboard and components, but also the CRT. Because of this, it's huge! You need a full width tower to be able to fit both the mainboard and the power supply. This is not something I wanted. The power supply which came in the Flex ATX case that I chose came with a 150W mini ATX power supply. It's about half the size of a full size supply from a large tower, although it uses a standard ATX power plug. The iMac on the other hand uses a much smaller connector with a lower number of pins. I didn't want to cut into the new power supplies harness in order to adapt the iMac's connector. Although this would in the end be a cleaner setup. I chose to go with an ATX extension cable, and then splice this with the original iMac power cable. This is the part that stumps a lot of people. But truth be told, it's not really all that difficult to get the power to the board (although it is more trickier to get it to turn on and off when you want as I will touch on later). I downloaded a copy of the ATX specifications datasheet (available here) and a copy of the iMac Service manual (available here) and compare the pin outs of each. Basically connect like wires. +3.3VDC to +3.3VDC, +5VDC to +5VDC, and so on and so forth. There will be some wires from the ATX supply, which do not go to anything on the iMac side. I will draw up a diagram at a later date when I have time.

The second part of hooking up the power supply is getting it to turn on. The iMac and ATX supply use different setups to turn on and off. The ATX uses a wire that grounds when you want it to turn on (green wire), while the iMac uses a 5V sense wire. I haven't had the time to do up a correct on and off setup (if anybody has access to a schematic of the iMac's power supply setup I would be forever in your debt :) So I am currently setup using the ATX's way of turning off and on. That green wire from the ATX supply will turn the supply on if you ground it. So you can either leave it always grounded via a screw or the like, or hook it up to a switch. If it's always grounded, the rear switch on the supply turns it on and off. If its hooked up to a switch, then the switch will turn it on and off. When I do come up with a way to have it turn on and off correctly I will be sure to post it here. OS9 does shut down just fine, screen goes black, drives spin down, etc. And when I boot it back up it doesn't come up with drive repair or anything.

UPDATE:

I have partially resolved the power on issue. I can now turn it on by using the button on the front of the ATX case. I did this by doing two things. First, I soldered the 2 wires from the switch in the ATX case to the backside of the iMac power switch (which is on the small board with the headphone jacks) I then purchased a Hex Inverter IC (Part Number at Digi-Key: 296-1205-5-ND). This will allow me to turn the 5V sense that the iMac needs into a ground circuit that the ATX supply needs. However, I need to put more time into it, as when I go to shutdown, the machine just restarts instead (meaning the ground for the ATX supply is not being broke. I will address this when I get time) Soon as I get time I will add a diagram for thee hex inverter and the power supply, as I have gotten request for both.

5. Cooling

For cooling I haven't come up with a final solution yet. I currently have a single 60mm fan blowing down onto the heatsink. (you can see the fan mounted flush with the power supply in the middle right photo above. It does run in spec with this setup, but it's not as cool as I would like it to be. I will be adding a larger heatsink (as large as I can fit back there that is) and possible another 60mm fan blowing horizontally across it. I will update this page as I improve on this setup.

6. Extras

Here is the rest of the stuff that I did. For video, I used the original video/sound distribution board. I had an old Mac to VGA adapter cable that was about 12 inches long. I hooked this up to the distribution board, then the VGA end out the back through a port that was meant for a serial connection. Works and looks good.

For storage I used a 60GB IBM 120GXP and a no-name 8x4x32 CDRW I had lying around. They are currently shared on the same ribbon cable, this being because I have been unable to find an adapter to go from the iMac's mini-PB IDE header to a standard IDE header. Although things seam to work fine currently, it would be nice to have the little extra speed gained from using both controllers.

I also hooked up one of the iMacs original speakers inside to the video/sound distribution board for simple beeps and such without having external speakers plugged in.

The rear panel was pretty easy to setup. I used the orginal iMac ports cover, and then used some of the CRT shielding that I removed from the iMac to use as a cover for the top area that the original cover left open.