I did not cover the second stage bootloader in my first post so i am updating to include a little more information about it. The 2BL , also known as the second stage bootloader gets decrypted by the 1BL (notice the pattern) and does basic hardware initialization , and stores a version number and allowed version number before moving to 4BL , it also runs a VM (virtual Machine). The important thing too know and the reason i made this post is that if this 2BL section is updated you can no longer run hombrew. Here is a table of exploitable CB versions , and un-exploitable versions and also the main-board that it corresponds to.
This list will be as complete as possible however bare in mind not every CB version is known , as their are many. The un-exploitable versions are however all known as their are less of them. Some of these I have added myself when i found them and will most likely not be listed anywhere in the forums , because it is not an organized place and things get lost when not needed by us anymore. So if you see a CB version not listed somewhere else it is not a typo it is from my experiences and what i have seen personally. You can e-mail me with more if you find them and i will add them.
Exploitable CB Versions:
1888 , 1902 , 1903 , 1905 , 1920 , 1921 , 8192 (Xenon)
4558 , 4540 , 4580 (Zephyr)
5760 , 5761 , 5766 , 5770 (Falcon)
6712 , 6723 (Jasper)
Un-Exploitable CB versions:
1922 , 1923 , 1940 (Xenon)
4571 , 4572 , 4578 , (Zephyr)
To find out your CB you must solder 7 wires to the main-board and read the NAND this is the last thing to check after you have confirmed that you have a compatible dashboard version. Anything made after Jun 18th 2009 will have this updated 2BL , and I have checked this too be sure. Another section which will be the same and un-exploitable on all un-exploitable machines is the “CD” section of 8453.