There's been a discussion thread on Xbox-Scene forums about a way to 'uncripple' your harddrive AFTER you got banned. As you know Microsoft decided to 'remove' some HDD features (like play games from HDD, etc) when your console gets banned.
Microsoft does this by modifying data in the secdata.bin on the NAND (that's why write-lock the NAND was a way to prevent HDD-crippling). But people found out the NAND has an older (backup?) copy of secdata.bin stored on the NAND as well. Now the hack consists of copying the old version of secdata.bin on the location of the new/current secdata.bin. Both secdata.bin are tagged with a date stamp so you can easily find out which one is the new and old one. As your console is already banned, it does not really matter if MS can detect this or not.
Thwack wrote a good tutorial for this
This is pure HEX editing in the NAND image, no CPU-key or whatever is needed. However, for those new in dumping the Xbox 360 NAND … if you do via LTP with nandpro, make sure to dump it a few times and compare to make sure your image is good.
Before wild stories go around … this does NOT unban your console from LIVE.
Read More: original thread | tutorial
Original Source: Xbox-Scene
found the best explination here
http://ep-comps.com/free60/xell/XeLL-JTAG-Hack_english.pdf