Bootloader Unlocking

Bootloader

Bootloaders are used to boot operating system on our device . Usually our phone's bootloader will be locked by Sony Ericsson during its production itself . Almost every custom rom we install has its own KERNEL which is responsible for overclocking the cpu & other stuff.To install custom roms which contains custom kernels we need UNLOCKED BOOTLOADERS .

Unlocking via Sony's Official website

Sony has provided a website where we get an unlock code for each IMEI no. type in that code and your bootloader will get unlocked officially . This is the easiest unlocking method possible . Wait there's more , official unlocking method does more bad than good , like
1. will void warranty
2. Will loose DRM & track Id related stuff
3. No official phone updates via SEUS/PCC or OTA 

If you don't care about them please go ahead and click this LINK and follow on-screen instructions on that site

RELOCK : 
If you unlocked ur xperia using the official method then relocking wont give you back the DRM Key's.


There is an alternative way to avoid the above mentioned limitations , it is called SEtool 


Unofficial Unlocking (S1tool)

This method overcomes all the three limitations , but you will need to do a little work manually , this method introduces us to a new word called TESTPOINT(Of all those 8 golden points , only the point which is indicated by the arrow is the TESTPOINT) .For NEO V testpoint is located deep within a slot covered by a black patch which is above our SIMCARD slot (see this picture and remove the black covering) .

It is used for function-test during production. & we are going to ground that testpoint using a simple wire .instead of that pin you can use any conducting material (wire , safety pin , paper clip , but make sure its diameter is not more than that of the testpoint else it will touch other points and might brick your phone)

Ground : ground is refereed as the negative battery pin of the phone 

Steps
1. download & extract SEtool from here [LINK 2] , [LINK 3] .
2. Connect test point to the ground and attach USB cable. Wait while Windows shows finding new device, disconnect test point immediately. Windows won't find appropriate drivers. select drivers manually from the archive of SEtool. Agree to install 'untrusted' drivers.
3. Reboot your PC
4. Run s1tool, press 'Patch semcboot' and follow tho on-screen instruction.

RELOCK : : ONLY THE RESTORE BUTTON PRESENT IN S1TOOL WILL RELOCK YOUR BOOTLOADER , other procedures will not work.Connecting TP to ground while using RESTORE button is not necessary.

EXTRA info : (thanks to DooMLord)

The method is same but the test points are different for different devices.

Test Points:

Cable Structrue:

Phone: SE LT15i Qualcomm

Testpoint

Phone: SE LT18i Qualcomm

Testpoint

Phone: SE MK16a Qualcomm

Testpoint

Phone: SE MT11i Qualcomm

Testpoint

Phone: SE MT15i Qualcomm

Testpoint

Phone: SE R800 Qualcomm

Testpoint

Phone: SE SK17i Qualcomm

Testpoint

Phone: SE SO-01C Qualcomm

Testpoint

Phone: SE SO-02C Qualcomm

Testpoint

Phone: SE SO-03C Qualcomm

Testpoint

Phone: SE ST15i Qualcomm

Testpoint

Phone: SE ST17i Qualcomm

Testpoint

Phone: SE ST18i Qualcomm

Testpoint

Important:

Connect the MicroUSB cable directly to your Phone do not use any hubs as the decrease the current(DC 5V) travelling to your phone from the USB port.