[Transformer TF300T General] pjc21:
After almost a full day of flashing I now have a 100% successful method of flashing any stock JB Firmware

With this method I have been able to successfully flash any stock JB Firmware from 10.4.2.9 all the way through to 10.6.1.27.5 without issue.

unfortunately you can not go back to ICS bootloader or firmware (there is a signature mismatch issue here).

Try this at your own risk, I will not be responsible for a bricked device.

Recommend doing NVFlash first so your tablet is Unbrickable

NVFlash for ICS bootloader

NVFlash for JB bootloader

Warning:

If you flash an incorrect recovery to a 4.2 bootloader there is about a 90% chance that fastboot flash commands will now just freeze the tablet - When you attempt to flash via fastboot everything will seem to go ok on the command prompt but you will not see the blue progress bar on the tablet when flashing & the reboot command will not reboot the tablet after the flash command & nothing will have flashed to the tablet.

If this is the case try this solution.

Please read below for how to check your bootloader version and confirm your flashing the correct recovery.

Requirements:

Must be unlocked (Method 1 seems to work fine for locked devices but must be unlocked for Method 2 to flash custom recovery).

Must have working fastboot

Working adb in recovery (optional). I use adb in this method for rebooting but this can be done manually with vol- & power.

Always make a backup first.

Files Needed:

Download the stock JB firmware you wish to flash from either the Asus website or from the Index thread here, be sure to download the correct SKU version you wish to use On your tablet you can check what SKU your using by going to settings>about tablet, scroll down to build number and you can see SKU version..

If using method 2 download the TWRP recovery you require, Here is a link to the TWRP thread. When you download a version of TWRP it will have a name like "openrecovery-twrp-2.5.0.0-tf300t-4.2.blob" - You can rename to something shorter for flashing if you like, I rename like so "twrp-2.5.0.0-4.2.blob".

What recovery to flash for bootloader version: example for TF300T model:

Check & confirm what bootloader your on - boot to bootloader menu (vol- & power) and look at the text in top left, your bootloader version number is there.

JB 4.1 firmwares

If current bootloader = 10.4.2.9 - JB 4.1 - recovery to flash = TWRP "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" or CWM

If current bootloader = 10.4.2.13 - JB 4.1 - recovery to flash = TWRP "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" or CWM

If current bootloader = 10.4.2.17 - JB 4.1 - recovery to flash = TWRP "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" or CWM

If current bootloader = 10.4.2.18 - JB 4.1 - recovery to flash = TWRP "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" or CWM

If current bootloader = 10.4.2.20 - JB 4.1 - recovery to flash = TWRP "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" or CWM

JB 4.2 Firmwares

If current bootloader = 10.6.1.8 - JB 4.2 - recovery to flash = ONLY TWRP "openrecovery-twrp-2.4.4.0-tf300t-4.2.blob" - flashing a non-4.2 version of TWRP or any version of CWM will brick device. Also flashing 2.5.0.0-tf300t-4.2 on the 10.6.1.8 bootloader results in a split-screen issue.

If current bootloader = 10.6.1.15.3 - JB 4.2 - recovery to flash = ONLY TWRP "openrecovery-twrp-2.5.0.0-tf300t-4.2.blob" - flashing a non-4.2 version of TWRP or any version of CWM will brick device.

If current bootloader = 10.6.1.27.1 - JB 4.2 - recovery to flash = ONLY TWRP "openrecovery-twrp-2.5.0.0-tf300t-4.2.blob" - flashing a non-4.2 version of TWRP or any version of CWM will brick device.

If current bootloader = 10.6.1.27.5 - JB 4.2 - recovery to flash = ONLY TWRP "openrecovery-twrp-2.5.0.0-tf300t-4.2.blob" - flashing a non-4.2 version of TWRP or any version of CWM will brick device.

My Notes about TWRP 2.4.4.0-4.2:

TWRP 2.4.4.0-4.2 will not mount my sandisk 64gb micro SDXC UHS-1 class 10 card, but previous versions of TWRP have no issue. I believe this is a UHS-1 issue. TWRP 2.5.0.0-4.2 has fixed this bug and and can now mount 64gb micro SDXC UHS-1 class 10 card again.

Method 1

Unzip the firmware zip you downloaded, there will be another zip file inside.

Example:

Lets say you choose WW 10.4.2.20 firmware. (same method apply's for any firmware version and SKU you choose - US, WW, JP, TW, CN)

[*]Unzip "WW_epaduser_10_4_2_20_UpdateLauncher.zip"and you will find another zip inside "WW_epad-user-10.4.2.20.zip".

[*]Now unzip the WW_epad-user-10.4.2.20.zip and you will find a "blob" file.

[*]Now copy the blob file to your android-sdk\platform-tools folder.

Now to the flashing:

With your device loaded in android go to settings, developer options and make sure they are on & usb debugging is on.

[*]Plug device into PC with usb cable & boot to fastboot.

Using adb commands

Open command prompt (run as admin) & cd to you android-sdk\platform-tools folder.

Check your PC can see your device

adb devices

You should get a list with you device s/n, if not then adb is not setup.

Next

adb reboot-bootloader

or

Manually boot to fastboot

Hold vol- & power button to boot to bootloader then connect to PC.

Fastboot will start automatically when connected to PC on the 4.2 bootloaders. On 4.1 bootloaders you will need to select the usb icon using vol- to highlight the usb icon and vol+ to select.

Note:

In bootloader NEVER select the Wipe Data icon or you will brick.

Once in fastboot open command prompt & cd to you android-sdk\platform-tools folder and type command

fastboot devices

and again here you should get a list with you device s/n, if not then fastboot is not setup.

[*]If OK we can now flash the system blob we put in the platform-tools folder

fastboot -i 0x0b05 flash staging blob

This will take about 10 minutes to send & write system, you will see a progress bar on device when system is writing.

[*]When complete

fastboot reboot

This method should work fine but have found that sometimes the device will get stuck at the boot animation, if this happens method 2 works fine every time.

Method 2

Unzip the firmware zip you downloaded, there will be another zip file inside.

Example:

Lets say you choose WW 10.4.2.20 firmware. (same method applys for any firmware version and SKU you choose - US, WW, JP, TW, CN)

[*]Unzip "WW_epaduser_10_4_2_20_UpdateLauncher.zip"and you will find another zip inside "WW_epad-user-10.4.2.20.zip".

[*]Place a copy of the WW_epad-user-10.4.2.20.zip on your microSD card.

[*]Now on PC unzip the WW_epad-user-10.4.2.20.zip and you will find a "blob" file.

[*]Now copy the blob file to your android-sdk\platform-tools folder.

[*]Now copy the "twrp-version.blob" file you downloaded to your android-sdk\platform-tools folder.

--Make sure you have the correct twrp version for the firmware your flashing.

Now to the flashing:

With your device loaded in android go to settings, developer options and make sure they are on & usb debugging is on.

[*]Plug device into PC with usb cable & boot to fastboot.

Using adb commands

Open command prompt (run as admin) & cd to you android-sdk\platform-tools folder.

Check your PC can see your device

adb devices

You should get a list with you device s/n, if not then adb is not setup.

Next

adb reboot-bootloader

Manually boot to fastboot

Hold vol- & power button to boot to bootloader then connect to PC

Fastboot will start automatically when connected to PC on the 4.2 bootloaders. On 4.1 bootloaders you will need to select the usb icon using vol- to highlight usb icon and vol+ to select.

Note:

In bootloader NEVER select the Wipe Data icon or you will brick.

Once in fastboot open command prompt & cd to you android-sdk\platform-tools folder and type command.

fastboot devices

and again here you should get a list with you device s/n, if not then fastboot is not setup.

[*]If OK we can now flash the system blob we put in the platform-tools folder.

fastboot -i 0x0b05 flash staging blob

This will take about 10 minutes to send & write system, you will see a progress bar on device when system is writing.

[*]Once this has completed type in the command prompt.

fastboot reboot-bootloader

You can now check that your bootloader has upgraded/downgraded, look at the text in the top left of the bootloader screen and make sure it's changed to the firmware version you just flashed.

[*]Now again depending on the bootloader version go to fastboot.

Next

[*]In the below command I am using "openrecovery-twrp-2.5.0.0-tf300t-JB.blob" for JB firmware 10.4.2.20, and shortened the name "twrp-JB.blob" so just change command according to TWRP version needed.

fastboot -i 0x0b05 flash recovery twrp-JB.blob

[*]Once this has completed type in the command prompt.

fastboot reboot-bootloader

[*]Now this time in bootloader select the "RCK" icon to enter twrp recovery.

[*]In twrp recovery select "Wipe".

[*]Here I do a complete wipe (cache, Dalvik cache, Factory Reset, System, Internal Storage & Format Data) I don't believe Internal Storage & Data Format are necessary but I like a full clean flash.

[*]Once you have done full wipe type in command prompt.

adb reboot-bootloader

or manually reboot to bootloader, hold vol- and power button.

[*]Now again in bootloader select the "RCK" icon to enter twrp recovery.

[*]In twrp recovery disconnect your device usb cable from PC.

[*]Select "Install" & select the firmware zip you copied to your external sd card and slide to flash/install.

[*]Once completed reboot, you will get message at top of recovery saying there is no OS installed are you sure you want to reboot - slide to confirm yes, another message will popup asking if you want root permissions installed - I select NO "Do not install" you can probably select yes here if you want twrp to root.

The device will reboot, you'll see a progress bar as the signature is being matched, it will reboot again when done.

Now device will boot with the stock JB bootloader & firmware you have chosen.

Done.

You can now flash twrp, then flash any custom rom for that firmware.

As I have said I have done this with all stock WW JB firmware available and can confirm that the bootloader does change and system will boot and run without any issues. But try at own risk.

Firmware I have done this with: Only tried with WW SKU

10.6.1.27.5

10.6.1.27.1

10.6.1.15.3

10.6.1.8

10.4.2.20

10.4.2.18

10.4.2.17

10.4.2.13

10.4.2.9

More Info:

Downgrading from CROMi-X back to CROMi-3.4.6

Upgrading from ICS to JB

If you this information is helpful please hit the thanks button.