1.4v A38727-012 MotherBoard - South Bridge / MCPX 3 Replacement, need help.

[TJ1]

Ok so I totally messed up this Xbox. It's so mint and it's a crystal edition. I modded it with a Smart XX mod chip and 400GB IDE Hard-Drive. I made it so I can easily unplug the mod chip and install the original Hard-Drive if I ever wanted to bring it back to original. Everything was working well. All I was doing was finishing it up. I'm upset because I cannot get it to work again and I am hoping someone here can help. Long story short, I had the Xbox open and the Hard-Drive was removed, I was going to re-install the Hard-Drive after copying a bunch of DATA to it and then it happened, I dropped the end of the IDE cable onto the power supply and seen a small puff of smoke. Yes, I had the power plugged in......big mistake.....rookie mistake..... I really don't want to "replace" the motherboard with another one. That's the lazy way and it won't be "original".... so please help if you have the knowledge and experience replacing major components on original Xbox motherboards. 

The voltage from the power supply spiked through one of the pins on the IDE cable. I know which one if it helps.... Ended up Killing the Phillips DVD drive and the main Xbox motherboard. 

Took apart the DVD drive. I figured, I'll take the lazy way and replace the mainboard in the DVD drive and call that a day. Maybe fix the original one later.

Now I still have the dead motherboard. I found one of the pins from the IDE port leading to the MCPX 3 South Bridge (Korea) was shorted. I don't have any schematics for this unfortunately, maybe someone could help with those. The line that is shorted I have removed the components causing the short. I removed RP6T1 and the MCPX 3 South Bridge. 

I have a 1.2v A38727-012 motherboard I am using for parts. I moved the RP6T1 and the MCPX 3 South Bridge (Taiwan) over to the "dead motherboard". Now the Xbox turns on and boots but will not complete. I am stomped with error 13 with the mod chip/400gb HDD setup. With the Hard-Drive un-plugged it gets error 07. Boots into my Smart XX bios. But that's it. Won't boot from a HeXEn DVD either....

With mod chip unplugged and with the original Hard-Drive, it gets the same error 13. Basically I know it's not an issue with the Hard-Drive's, or mod chip. I tested the mod chip and Hard-Drive in another Xbox 1.4v. I also checked all my solder work. The MCPX 3 worked fine on the parts motherboard...

I tried a different DVD drive, DVD power cable, IDE cable, Xbox PSU. The motherboard still has an issue. I just don't know if there is anything special I have to do after swapping a MCPX 3. I know in newer motherboard of PC, that when changing a south bridge that the ME region has to be cleaned. I just don't have a lot of experience with PC's older than 2008. 

Is the MCPX 3 from the 1.2v not compatible on the 1.4v? I am pretty sure they are both the same part.. Only difference is where they were manufactured. 

[jjjwelch]

There has to be some mis-match on the software level I'm thinking. Seems like it's trying to talk to something, and it's not getting the expected response. Reminds me of smc issues on the 360 

[TJ1]

I moved over the ROM and TSOP from the 1.2v motherboard to the 1.4v and have run into the same issue. Maybe I need to transfer over the GPU or CPU as well? The PCB layouts between 1.2/1.4v look the same.

 

I'm thinking of getting a donor 1.4v motherboard with MCPX 3 (Korea) and trying the swap again... I think it has something to do with the MCPX itself...

 

 

 

[KaosEngineer]

22 hours ago, TJ1 said:

I moved over the ROM and TSOP from the 1.2v motherboard to the 1.4v and have run into the same issue. Maybe I need to transfer over the GPU or CPU as well? The PCB layouts between 1.2/1.4v look the same.

 

I'm thinking of getting a donor 1.4v motherboard with MCPX 3 (Korea) and trying the swap again... I think it has something to do with the MCPX itself...

 

 

 

Didn't the first level boot loader and decoding key and algorithm change between a v1.2 and 1.4 motherboards?  Or was that just v1.0 to later revs then again with v1.6 motherboards.  

512 bytes of code are stored in a permanent masked ROM that is part of the MCPX3 chip.  It contains the first-stage boot loader (1BL) , decryption algorithm of the second-stage boot loader (2BL) decryption key(s), and X-code interpreter.

For more about the boot process of the Xbox read Matt Borgerson's archived write-up available on archive.org's Wayback Machine:

https://web.archive.org/web/20220518102811/https://mborgerson.com/deconstructing-the-xbox-boot-rom/

 

Edit:

Excerpt from Microsoft's Copilot's reply when queried aboiut deconstructing the xbox boot rom:

Certainly! Let’s delve into the fascinating world of the Xbox boot ROM. 

1. Xbox Boot ROM (MCPX):

   • The Xbox has a 256 kiB ROM that contains the startup animation, sound, and crucial components like the kernel.
   • The kernel is a stripped-down version of the Windows 2000 (NT 5.0) microkernel.
   • When you power on the Xbox, the software in the ROM is decompressed into RAM, and the kernel initializes the hardware¹. (Reference: Boot Process - xboxdevwiki)

2. MCPX Versions:

   • There are two known versions of the MCPX ROM: 1.0 and 1.1.
   • The 1.0 version, found in the original Xbox, used an RC4 algorithm to decrypt the 2BL (second bootloader).
   • For the 1.1 version, Microsoft switched to a TEA algorithm². (Reference: MCPX ROM - xboxdevwiki)

From the information provided above, one would think that a v1.1 or later motherboard rev's MCPX3 would work on any v1.1 or later motherboard.