[Transformer TF300T General] joelalmeidaptg:
Asus released the new Android 4.2 to our beloved devices and you may be wondering how can you update if you are unlocked and how can you root it.

Note: this guide was updated with the 2.5.0.0 TWRP. For this to work properly, you will need to use the last 10.6.1.27.1 version of the tablet, or a newer one. If you are already on a previous 4.2.1 version, please update to the new one using this same guide. If you flash this recovery with the older versions of the 4.2.1 bootloaders, you will end up with a double screen! New TWRP versions won't be able to mount boot and recovery, and won't work with all SD cards, not to talk about backup issues!

Things you should know before you start:

- I marked each title of this guide with [LOCKED BL], [UNLOCKED BL] and [BOTH BL] to specify witch ones will work with locked/unlocked or both bootloaders, respectively.

- Please verify if you have the correct drivers for the tablet installed on your computer. Windows 7/8 should install these automatically.

- The new 4.2 updates the bootloader, removing the USB icon that used to appear there and allowed you to enter fastboot. It's OK, you will be able to use it right from the bootloader menu, without selecting any option at all.

- Do this at your own risk! I'm not responsible if you break your tablet!

- Don't forget to make BACKUPS!

- If you are already on 4.2, then you can skip to the Recovery and Root parts of this guide

-- Installing / Updating to 4.2.1 --

There are three methods you can use to update your tablet to the latest Android stock version. All of them will require you to download the

firmware file located at Asus website. You can download them from here. Select Android as the OS, firmware and choose the right firmware for you SKU. You can find your SKU by following the instructions on the website itself. Don't forget to unpack the zip file you downloaded: there's another inside!

[BOTH BL] Method 1: Updating directly from stock ROM

Notes:

You must have a stock ROM installed

You need to put the update file on an SD card

You will keep all your data

I do not recommend this method: sometimes it ends up on a brick

If your tablet is stock, or have some custom ROM based on stock installed, you can directly update the tablet by simply inserting a SD Card with the firmware file inside. Android will prompt you with a notification asking if you want to update. Touch it and wait until the update is done

[UNLOCKED BL] Method 2: Update using fastboot

Notes:

You will keep all your data

This is the best method to update your tablet if you want to keep all your data, and the safest one

Ensure you have the correct drivers for the tablet installed on your computer, or you will have a "waiting for device" error

To update using fastboot, follow this steps:

If you don't have fastboot yet, download it from here an unpack it somewhere on your computer

Extract the Asus firmware file and put the blob file inside fastboot folder

Open a command line on fastboot folder (write "cmd" on Windows search bar at the Start menu, and then

cd "FOLDER WHERE YOU EXTRACTED FASTBOOT"

, or you can just use SHIFT + RIGHT CLICK on the folder and select "Open command line window here" or something like that)

Reboot the tablet holding the volume down key until you see some icons. Use the volume down key to select the USB icon and then volume up to select it

Connect the tablet to the computer if you didn't do so

Write

fastboot -i 0x0B05 flash staging blob

, hit enter and wait until it completes

Hold the power button for 10 seconds to reboot the tablet

You are now updated to Android 4.2

[UNLOCKED BL] Method 3: Update using TWRP recovery

Notes:

You must have TWRP installed

You need to put the update file on an SD card

This was the method I used since I wanted to prevent any bugs due to old data and to ensure the new partitions from 4.2 would be OK

You will keep your data as long as you don't wipe Data and Factory reset (including internal memory)

Follow the steps bellow if you want to update to 4.2.1 DELETING ALL YOUR DATA , STARTING FROM SCRATCH!

Insert the SD card with the update file on the tablet

Reboot to recovery

Wipe Cache, Dalvik and System. Wipe Data if you want a fresh start on your tablet, but remember, THIS WILL WIPE ALL YOUR DATA AND INTERNAL MEMORY!!. You can also do a Factory Reset instead of data wipe if you want to remove all your android configurations/apps keeping your internal storage.

Install the Asus Firmware

Reboot (ignore the "no OS installed message) and let it finish

You have now the latest Android 4.2.1

[UNLOCKED BL]-- Installing TWRP (Recovery) --

Since this new update brings a new bootloader, older recovery versions from 4.1 won't work at all. Don't try to flash one!

This guide will give you a recovery that works just fine on the new bootloader. And yes, it can read/write to an external SD just fine. Follow this steps to install the new recovery on your device:

Connect the tablet to the computer

Reboot the tablet using the proper button on the power menu, holding Volume down until you see three icons (RCK, Android and Wipe Data)

Download this file and unpack it (it contains fastboot and the TWRP 2.5.0.0 which works with the new bootloader)

Open a command line on the extracted folder (you can use the instructions I wrote in Method 2 if you don't know how to do this) and type

fastboot -i 0x0b05 flash recovery twrp.blob

Wait for the script to complete. Once it is done, reboot the tablet by holding volume down and power button for 10 seconds. Don't enter recovery directly!

You have now the new recovery for Android 4.2 .

[BOTH BL] -- Rooting --

Note: If you are willing to install a custom ROM like CROMI you don't need this. Custom ROMs have root by default.

Rooting the tablet once you have a recovery is pretty easy. Here's how you can do it:

- Unlocked devices

Download SuperSu zip file from here (choose the flashable version) ]and place it on a SD card or inside the root of your tablet's internal memory

Reboot the tablet holding vol down, and when the three icons appear, hit volume up to enter recovery

When the recovery prompts you a password, hit cancel (this is a bug from the current version of TWRP, and it should be fixed soon. It is ok to ignore it!)

Flash the zip you just downloaded

Wipe Dalvik/Cache (just in case)

Reboot

You are now rooted!

- Locked devices

If you have your bootloader locked you can root Android 4.1/4.2 by using the method discovered by Morlok8k, here: http://xdaforums.com/showthread.php?t=2228613 (note that this isn't tested yet for the latest 10.6.1.27.5 firmware!)

[UNLOCKED BL] -- Downgrading to 4.1 or other firmware --

I was going to write a downgrade method but it seems that there is a good one here: http://xdaforums.com/showthread.php?t=2195883

Again, do it at your own risk.

[LOCKED BL] -- Recovering your tablet from scratch --

If you are on a stock locked device and somehow got a bootloop and you can't do anything with your tablet you follow this steps to completely restore your tablet. Note that all data will be lost.

This tutorial is made of things I gathered on the forums: I do not own anything! Hit thanks if I helped you :angel: I will keep it updated once new things come out

A special thanks to elesbb for the fastboot methods ;)