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Hola todos, os traigo un tutorial probado por mi que funciona de como poner la rom oficial del Xperia L sin las personalizaciones de las operadoras como movistar o vodafone.
SI TENIAS EL TERMINAL ROOTEADO, ESTE SE PIERDE
Vamos por pasos:
1º Hacer backup de nuestro firmware original ( No explico como ya que hay un fallo y no se puede hacer)
2º Descargar la ultima versión de Flashtool e instalarla:
http://xperiadownload.cz/index.php/x...gory/5-ostatni
Es necesario registrarse en la pagina para descargarlo
3º Descargar la ultima version del Firmware de Sony para nuestro Xperia:
http://xperiadownload.cz/index.php/x.../category/33-l
Es necesario registrarse en la pagina para descargarlo
4º Ir al directorio donde esta instalado el Flashtool:
Descomprimir C2105_15.0.A.1.31_CE.ftf de la descarga del paso 3 y moverlo a la carpeta firmwares del flashtool
5º Abrir Flashtool(no conecctar el movil todavia pero si apagarlo):
-Pulsar el rayo arriba a la izquierda y sellecionar flashmode
-Seleccionar el firmware C2105
-Desmarcar DATA sino quieres perder todas las aplicaciones que ya tenias instaladas (Las de movistar y vodafone si desparecen, por que esas son del sistema)
-Puede dar algun fallo si se desmarca DATA pero por lo menos a mi ningun fallo
-Darle a Flash
6º Esperar a una ventana que pida conectar el movil (no conectarlo):
-Con el movil apagado, pulsar el boton de bajar volumen y conectarlo manteniendo pulsado el mismo boton hasta que Flashtool detecte el movil
7º Esperar a que termine:
Podeis desconectar el movil cuando ponga esto:
Ya estaria el terminal con el nuevo firmware, ya solo queda encenderlo y disfrutar 
Saludos
comentarte que yo he hecho sin problemas el backup del firm original de movistar siguiendo estos pasos:
Part B: downloading firmware with Sony Update Service
Requirements:
Sony Update Service
Xperia smartphone with locked bootloader
Delete the folder 'C:\Program Files (x86)\Sony Mobile\Update Service\db' if it exists.
Start Sony Update Service.
Accept the agreement, click 'Start', select 'Xperia Z', click 'Next'.
Follow the on-screen instructions to connect your Xperia Z.
If you are currently using an old firmware version, you can choose the 'Software update' option. Otherwise you will have to choose 'Factory data reset'. Click 'Install'.
If you just want to download the firmware without flashing it to your phone: watch the download progress very closely. When the end is near, start holding the USB connector. As soon as the download is completed (see screenshot), IMMEDIATELY DISCONNECT YOUR PHONE. Timing is crucial here. If you disconnect it before downloading is finished, the download will stop. If you disconnect it too late, you might lose data. I used this method several times without losing any data. My experience is that the download progress bar suddenly goes to 100%, before you would expect it, so be prepared!
There should be five 'FILE_*********' files in 'C:\Program Files (x86)\Sony Mobile\Update Service\db\13740270\blob_fs'. This is the downloaded firmware. If you want to create an FTF, copy these files to a separate folder.
Part C: creating an FTF file with Flashtool
Requirements:
LATEST Flashtool for Xperia Z
Firmware files from Sony Update Service (part B).
Start Flashtool or Flashtool64 (for 64-bit systems).
Click 'Tools' > 'SEUS Decrypt'.
Select the folder containing the firmware files from Sony Update Service as 'Source Folder'.
Move all 'Available files' to 'Files to convert' by selecting them and clicking the right arrow button.
Click 'Convert' and wait until the 'Bundler' window appears.
Enter the following details:
- Device: enter your phone model, e.g. 'C6602' or 'C6603' for Xperia Z (printed at the bottom of your phone).
- Branding: can be found in the first columns of these tables by looking up the customization number, e.g. 'Generic UK'.
- Build: the build number (version) of the firmware, e.g. '10.1.1.A.1.253'.
Move all files from 'folder list' to 'Firmware content' EXCEPT 'simlock.ta' by selecting them and clicking the right arrow button.
Click 'Create'. After creation has finished, your FTF will be in 'C:\Flashtool\firmwares'. If your combination of device/branding/build is not on xda-developers forum yet, please be so kind to share it (part D).
sacado de este post de xda:
http://forum.xda-developers.com/show....php?t=2311211