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So in my quest to stuff a computer inside an Xbox I decided to take the hard road and reuse as much as i can from the original Xbox. My original plan was to reuse the power supply, RF board, hard drive bay, and front USB ports. But due to heat concerns and f-ups on my part I doubt i will be using the hard drive bay or the usb ports.

So that just leaves the power supply and the RF board. I have some leads on the RF board from this thread: Attach RF Board to PC but it looks like this will be a whole ordeal unto itself. Now as for the power supply, after a full weekend of frantically cutting, soldering, and breathing led laden fumes i have the computer together and working with the Xbox 360 power supply! 

Step 1: Gather the parts

I decided to use use a standard blank circuit board as the base to put everything on so that i can solder the connectors together without having to deal with mounting. I also decide to grab some molex connectors make it so that the entire thing can be disassembled and reassembled quite easily.  

For my build i am using the folowing parts. These can be modified slightly to suite the power requirements of the mobo you are using. 

  • 1100ohm resistor
  • 1N914 or 1N4148 Logic Diode ( can't remember which one i used )
  • 2N3906 PNP transistor
  • 2.2uf 50V max capacitor

Step 2: Unsolder the connectors from the Xbox motherboard. 

I tried using an oven at 375F originaly but it didn't work out so well because the plastic started to get soft on me. So i went out and bought a butane powered solder iron and got each one out by hand. 

Step 3: Test fit! 

I really am starting to like the Mini-ITX AMD A-Series combo. Its very, very tiny and should be fast as hell.

Step 4: Let the wiring of the power supply begin!

Now before i begin i should say that i'm using this document to determine the pin-outs of the Xbox power supply: http://dwl.xbox-scene.com/tutorial/Xbox_360-HandC-V1_4.pdf
HOWEVER: This explanation for the diagram is not correct! It says that you need to ground pin 7 in order to turn the power supply on. What you actually have to do is feed the 5v from pin 8 to pin 7 and keep it there. 

Now this step is quite difficult because of the stupid way Microsoft decided to handle the standby mode on the power brick. For those of you that don't know the Power Brick will turn off all its 12v output when it deeps itself not in use. Luckily it will still output 5v even in this mode. This is indicated on the power supply be the orange light. Unluckily though the only way to turn the power supply on and keep it on is to feed the 5v into its neighboring pin. Why this sucks is because with standard ATX Power Supplies ( and by standard i mean EVERYONE ELSE ) the motherboard flips the power supply from standby mode to active mode by grounding the PS_ON pin.  

So what we have to do is somehow create a circuit that feeds 5v into the correct pin on the Xbox power supply when the PS_ON line drops to ground. The tricky part here is that the PICO PSU takes a single 12v line and does not have the ability to feed it the 5v standby power. Also when you splice the 5v from the Xbox power supply to the ATX cable the Xbox PSU faults out and shuts off. Well thanks to a little help from SD Electronics here in San Diego i have a working circuit that powers up both the Pico PSU and the Xbox PSU when the power button is pressed on the motherboard. 

EDIT: Here is a better diagram, still don't have a scanner though!

Here is a circuit simulator showing how it behaves.  Note: You need JAVA to run the applet!

Now this is pretty strait forward except for 1 thing. The capacitor connected to ground above the diode is used to store the minute charge that gets by the diode so that when the motherboard drops the PS_ON pin to ground the Xbox PSU has time to come online before the PICO PSU flips itself on and then realizes it doesn't have enough power and aborts the startup by failing to send the  PWR_OK signal to the motherboard.  The size of the capacitor does not matter, the larger it is the longer it will take for the voltage to drop to zero after the circuit has been grounded and hence the longer it will take for the Pico PSU to start. 
So to set this up do the following things:

  • Connect pin 8 on the Xbox PSU to pin 9 ( +5Vsb purple )  on the ATX Power Cable at the motherboard side. Do not splice but instead cut the wire so that only the motherboard ATX is connected to pin the Xbox PSU pin 8. 
  • Connect pin 8 to the emitter ( pin 3 ) of the PNP transistor. 
  • Connect pin 7 to the collector ( pin 1 ) of the PNP transistor. 
  • Build the circuit described above. 
  • Cut the wire for pin 14 ( PS_ON, green ) between the mobo and the psu.
  • Attach the Pico PSU side of the PS_ON wire to between the diode and the capacitor shown above.
  • Attach the mobo side of the PS_ON wire to the far side of both diodes shown above. 

That's it! You can see my test of the circuit here below! Please Note that the capacitor is not connected correctly in this photo. 

It seems i forgot to take photos of the completed soldered in circuit but i will as soon as i get a chance! 

Step 5: Power it up!

As noted before the power button now activates the motherboard and power supply at the same time! As for the RF panel and xbox power button i'll get to that in a latter part of this build.

Here it is all together!

Now i've been told before that the Xbox case is a bad design but god damn this thing sucks. Even with a big hole in the top and two other fans i'm still having problems keeping the system below 50C!
 
More to come when I get the RF board working!

EDIT: Updated the live circuit diagram, list of materials, circuit wiring instructions, circuit diagram, links to the previous parts of this project. 

Here are the links to the other parts of this build, check them out!

Part 1: http://wetzelrice.com/blog/build-an-htpc-in-a-xbox-360-part1

Part 3: http://wetzelrice.com/blog/build-an-htpc-in-a-xbox-360-part-3-finishing-up