Tutorial written by : hammy

For whatever reason you have, you have decided to put in a homebrew chip using a PC motherboard. Ok great, now you want to put in a disable switch, not to mention a switch to move between bioses and before you know it you have 18 switches and coffee maker sticking out the side of your box. Well, for my setup I’d like to keep things simple, on the outside at least. The theory here is to combine the disable switch and the dual bios switch into one easy to use unit; this is how I accomplished it.

First the things needed, normal equipment used in mod installation, 32pin DIP FlashROM, Center Off Switch (double pole), Strip board and Inverter IC (NOT gate). All of these can be found at a local Radio Shack, with the exception of the FlashROM. A good tip for people have trouble find things they need at radio shack, if they don’t have it ask them where the largest radio shack in your area is. I had to drive 15 miles away to get anything that I needed, although I have 2 Radio Shacks in my area.

Mount the IC, and FlashRom on the Strip Board by soldiering them in place, be sure to leave enough room between the components. I’d suggest using some sort of socket with the FlashROM instead of soldiering it down to the Strip Board, I installed a ZIF with mine. Then follow the Diagram, keeping in mind that this is intended for a FlashROM not an EPROM. Be sure that ALL appropriate steps are taken for EPROM’s.

*Note at intersections differing colors DO NOT connect
*Note that pin 16 IS NOT linked to pin 24 and 22, this IS INTENED

1.) Connect pin 1 on FLASHROM to center pole on switch
2.) Connect pin 32 on FLASHROM to either pole opposite that of center pole where pin 1 is connected
3.) Connect pin 16 on FLASHROM to remaining pole where both pin 1 and 32 are
4.) Connect pin 14 on Logic IC to Pin 32 on FLASHROM
5.) Connect pin 14 on Logic IC to Either pin Opposite of center pole
6.) Connect pin 7 on Logic IC to pin 16 on FLASHROM
7.) Connect pin 1 on Logic IC to pin 16 on FLASHROM via 10k resistor VERY IMPORTANT STEP!
8.) Connect pin 1 on Logic IC to center pole on switch
9.) Connect pin 2 on Logic IC to pin 24 on FLASHROM
10.) Connect pin 2 on Logic IC to pin 3 on Logic IC
11.) Connect pin 3 on Logic IC to “Link to 32” spot on Xbox motherboard
12.) Connect ALL UNUSED INPUTS ON IC TO pin 16 on FLASHROM
13.) Install chip normally, with out the “Link to 32” spot of course, and DO NOT link pin 16 on FlashROM to pin 22 and 24!
14.) Mount switch and chip where ever needed
15.) I also added 10uF Tantalum Capacitor between pin 16 and 32 on the FLASHROM that is not diagrammed above.
16.) Use larger diameter wire for pin 16 to motherboard, pin 32 to motherboard, and all connections going to the switch

AGAIN, to avoid from frying things DO NOT link pin 16 to pins 22 and 24 on the Flashrom, Connect only pin 3 on IC to “Link to 32” point, Connect ALL unused INPUT (e.g. NOT the OUTPUTS and MOST CERTAINLY NOT BOTH input AND output) pins on IC to pin 16 on FlashROM (CMOS chips anyways, and if you buy it from Radio Shack it’s more than likely to be CMOS), if you have an EPROM make ALL changes needed, the 10k resistor is VITIAL. So if you ever wondered what melted plastic smells like, or you like smoke to pour from your $200 xbox feel free to skip any of the above steps.

So now when the switch is in the Center (OFF) position the Xbox will boot from the normal bios disabling the Mod, whereas if the switch is in either the Up or Down position it will boot the appropriate half of the ModChip. Every thing worked for me like a charm, if anyone tries this project or any tips on making things better email me at hammy@priest.com

The whole process is rather cheap, I believe that the entire project cost about 10 to 12 dollars most of the cost was for the 4mbit FlashROM and a ZIF socket (optional). And it can easily be built with a lot of stuff you just have sitting around or can get that same day, all you really have to order is the FlashROM.