I built an Xbox out of spare parts and a motherboard given to me (basically meaning free), and here is my story of how it came to be a fully functional Xbox from nothing but this:

So here I am with an Xbox motherboard with the bottom plastic case and power/eject buttons. Now what?

I have no idea that this is a working Xbox motherboard, so the first order of business is to find a way to supply power to it (freely, because I'm the cheapest guy alive).

After many hours searching the vastness of the internet, I found some information on xbox-scene.com about adapting a PC ATX power supply for use in an Xbox. The exact thread might go down someday (plus it's a pain to read all that), so I'll duplicate the instructions for building such an interface here (I take absolutely no credit for this):

The thread goes on to say that R3 should be ommitted and R4 should be changed from 4.7kOhm to 1kOhm.

All of these parts are available from Radio Shack except for the L78L33AC, so here is a diagram (from the same thread) showing how to use an LM317T and a few resistors (which are available at Radio Shack) instead:

Using this diagram, R1 is 240Ohm and R2 is 390Ohm. Try and get values as close to these as possible.

Also, note that the diagram is for version 1.0/1.1 Xboxes. Mine happens to be 1.3 (best guess, anyway, since it has a Conexant chip), so I used the following tables (also from the thread) to adapt the pinout appropriately:

It seems that the POWOK signal doesn't need to be connected, but do it anyway. :)

After a lot of soldering and misplaced rage, I managed to build the circuit and hook up the power supply to it, and it turned on with a flashing orange LED! (Is it supposed to do that?)

As it turns out, yes, it does do that. I discovered that the Xbox will boot with a flashing orange LED if the A/V cable is not hooked up. Seeing as how I don't have an A/V cable, this was a problem.

I'm feeling good at this point because I have an Xbox capable of thought (in so far as being smart enough to flash orange at me without an A/V cable). My next task was to find a pinout of the A/V port at the back of the motherboard, and as luck would have it, I found exactly that.

I managed to find a description of the Xbox A/V connector on the underside of the motherboard. The Xbox is able to complain about no cable connected because the cable grounds the proper mode select pins, so they need to be grounded along with attaching audio/video cables. I soldered a wire connecting pin 19 and one of the grounding pins so that it would think an NTSC mono cable was attached. Then I was able to get a video signal and the left audio channel.

Soldering some CAT5 wire (very carefully) to the right pins (including the mode select one) and RCA connectors to the cable gave me a way to see the Xbox flubber as it booted! Picture of poorly-constructed cable below:

But right after that, I was greeted to a screen like this:

Panic ensues, but not too badly since I've yet to hook up a DVD drive or hard drive.

At this point, I've managed to get the Xbox to boot up and talk to me. Unfortunately, I couldn't tell it anything, since I didn't have a controller. I could've found a way to do this for free, but that would've taken way too much time, I'm sure. So I broke down and bought a cheap third-party controller. (I got it to turn on and work, so it's worth a couple of bucks at this point.)

Once I got that out of the way, I hooked up an old 10GB hard drive and a broken (meaning it can't burn) DVD burner via IDE cable and the ATX power supply. After that, the error code changed to one meaning the hard drive was unlocked. What's this? Hard drive unlocked?

After a whole lot more reading, I discovered that the hard drive which comes with the Xbox is "locked" to that particular Xbox. Since I have no idea where this motherboard came from, I have to figure out a way to "lock" my own drive so that my Xbox will like it. Unfortunately, the Xbox generates the lock/unlock key from information in its EEPROM, and without a modchip, there is no way to get at this information or boot the Xbox...almost.

I found a schematic to build a PC serial cable to extract the contents of the EEPROM. Yay! I soldered wires directly to the EEPROM and read off the information (pictured below for the coolness factor):

What came next was a real mess. I had to use a program called xboxhd to use my PC to lock the hard drive. I also found out that the hard drive I was trying to use couldn't be locked. So after going insane trying every hard drive I owned and every PC I had to get this frigging thing to lock, I finally found a 13.6GB drive and a frustratingly-crappy PC which worked.

So I have a functioning Xbox happy with the hard drive and DVD drive...I turn it on and I get another error code. Now what?

Now it just needs something to boot. I downloaded the Evolution-X dashboard from "the usual places" and went through a rather scary hotswapping process to get it on the hard drive. (I had to do this because the PC I used to lock it stubbornly wouldn't unlock it back. It's a real mess and the fault of my stupid PCs more than the project, so I'm not going into much detail.)

After that, it booted Evolution-X quite happily! I *cough* acquired *cough* some games and tried them from within Evolution-X (the first being Burnout 3: Takedown), but they didn't seem to work. Evolution-X kept saying the DVD drive tray was open, even though it wasn't. What? What's this?

I scratched my head trying to figure out what in the world was happening, but I finally realized that I was neglecting to use the DVD power connector near the back of the motherboard. This isn't just a power connector like I thought; it also has signals for knowing when to eject the tray, whether it is closed/open/ready, etc. Since I had no real Xbox DVD cable to splice, I had to find the pinout for this connector and supply the correct voltages directly. The pinout I found for this is below:

After soldering wires directly to the tray in/out and eject pins and supplying near +5V using AA batteries, Evolution-X and the Xbox were suddenly happy. A picture of my solution is below:

Pull the batteries out to "eject" the tray, and insert them to push the tray in. Incredibly crude, I know, but it's cooler that way.

Yes! It worked perfectly! Yay! A working Xbox from (almost) nothing!

At this point, I went crazy playing games. Lots of games.

Anyway, once I got that out of my system, I made some minor improvements, like switching to a micro-ATX power supply, replaced a dead hard drive, the official yellow DVD power cable, the official Samsung DVD drive, modchip, official controller, and other things. Some of those changes are shown in the pictures below:

All that's left is to put it in a real case. It obviously can't fit since it uses a micro-ATX power supply among other things, so I intend to build a case. When that's done, pictures will go up and this project will be officially complete.

I hope the information here is of some help to somebody, or at least entertains them. Feel free to e-mail me if you have any questions about it all.