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| Tonka iMac |
| Written by John Klos | ||||
| Friday, 01 September 2006 | ||||
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Once upon a time, I lived in New York City with more time than money. I had an old PowerBook 1400 which, of course, doesn't run OS X, and I wanted very much to have my own OS X machine (I'm a Unix geek). A friend who owed me a few dollars was working for someone who was gutting an iMac (not sure why), and he knew that I like to tinker, so he saved the motherboard, CPU card and that odd looking board with the power supply RF choke. In a scene out of a movie, he met me in a cold, rainy, dark winter evening in Times Square to give me the goods. Having more time than money comes in handy when you have parts and no documentation. This was many years ago, so some of the iMac pinout and information pages on the Internet didn't exist yet. But a multimeter and a lot of patience helped me get started with figuring out what was what with the power supply connections. Looking at the CPU card, it's obvious that without some airflow the heat sink would simply be too small to effectively keep things cool. So, since I had a few PC power supplies lying around, I decided to use one that had a rather large fan which was on the larger face of the supply rather than on the back where the power comes in. I imagined mounting the motherboard on top of the power supply upside down so that the fan drew enough air past the CPU card that an extra fan wouldn't be necessary. I was even able to overclock the 266MHz CPU to 333MHz without any stability issues. 
The shape of the power supply and motherboard made me wonder what kind of case would be ideal for this computer. While wandering around a store, a nice metal Tonka truck caught my eye and it immediately occurred to me that the motherboard on the power supply shape would fit perfectly in the back of the Tonka. $15 worth of an exchanged present later, I had a Tonka to go along with my computer in progress. Figuring out the pinout of the iMac for connection to the ATX power supply took a bit of time, but nowadays that would be considerably easier since there are many sites with the pinouts, like here. I decided to solder the wires to the RF choke board for two reasons: I didn't have the kind of connector that mated to that board, and because using the board meant that I could disconnect it from the motherboard pretty easily. As a Unix admin, I saw no reason to support soft power; the machine will be on, and can do a soft reboot of itself if necessary, but I couldn't imagine a reason why I'd want it to be able to turn itself off. I soldered the ATX power on wire directly to ground so that when the power switch was on, the power supply would always be on. 
Securing the power supply was easy. I didn't need anything fancier than double sided foam tape, since it was very likely that I wouldn't ever need to remove it. I left room in front of the power supply for the hard drive, which I secured by installing into a hard drive bracket from a Quadra 605 (don't worry - the Quadra's parts went into another interesting project!) Radio Shack sells plastic locking tape that allows removal, but is much stronger than Velcro. This seemed appropriate for the hard drive. I used blank metal covers used for PCI / ISA slots to mount the motherboard, again opting for simplicity. Double sided foam tape holds the front mount, as can be seen here: 
The back mounts each have a hole drilled in them, allowing thumbscrews to be used to secure them to the power supply: 
The 15 pin VGA connector wasn't too hard to figure out, and a tidy cover is used to hold the connector on the side of the truck: 
I never was able to figure out the audio connector, so I ended up getting a Griffin USB audio interface as a gift. Also, I couldn't find a proper cable for connecting anything to the iMac motherboard's second IDE bus this s usually used for the CD drive. Instead, I use a hard drive and a Combo drive on the main IDE bus, with the only issue being that I have to make the Combo drive master if I want to be able to boot off of it. Here's the Tonka in the process of installing OS X: 
This was my main computer for many years. After moving and getting a new job, the Tonka became my primary work computer and ended up becoming the office file server, so some upgrades were in order. Memory went from 192 megs to 512, and I bought a Sonnet Harmoni, primarily to add Firewire. After reading about Intech's LBA-48 driver that supports large hard drives on older machines (including the iMac), I got two 500GB drives. Adding XpostFacto to the mix, I am able to have a small partition with Classic at the beginning of the disk which lets me boot using a much larger (40 gig) partition for OS X and applications. The User's partition, thanks to the Intech driver, is 400GB. 
One of the 500GB drives is connected to the main IDE bus, with a Sony DVD burner connected as a slave on the same bus. The second hard drive is connected via a Firewire bridge which came out of an enclosure with a bad power supply: 
When people started complaining about not being able to log in because the 10 user limit was reached, I got a hold of OS X Server 10.3 from eBay for a nice price and installed that. Now the Tonka provides file and print service for 40 offices, plus accounts for transfer of files over the internet for many more people outside of the office. Even if I eventually get a new machine, this computer will always be needed and in constant use. It's very satisfying to imagine the computer I built in use years from now. The iMac Tonka has been incredibly stable, which lead me to choose the iMac motherboard when I wanted to build a tiny 1U server to colocate in Europe. That machine will be covered in a future modding installment... 
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