[Xperia Z3 Tablet Compact Android Development] lowtraxx:
Disclaimer: This procedure involves a higher risk than normal to brick your device. If you are not really familiar with flashtool please do not attempt to do this! I am not resposible for bricked devices, World War III or your exploding cats!

Also you acknowledge this points:

- This tutorial includes flashing the system partition of a firmware that is for a different device (Z3 Phone D6603)

- At some point your screen will not display anything

- This will not work on non-LTE versions of the Tablet (SGP611 and SGP612). Instructions for SGP611 can be found there.

- You also will loose all of you data, so please make a Backup.

If you are still sure you want to do this then here are the Steps:

1. Get the firmware ftf (SGP621_23.0.1.A.0.167_CE.ftf) for the SGP621 (for example from here or here)

2. Get a vulnerable firmware ftf (D6603_23.0.A.2.93_Generic_20GLOBAL.ftf) for the Xperia Z3 D6603 (for example from here or here)

3. Get the patched giefroot version for our device here

4. Open Flashtool and select flash. Then select flashmode and press OK

5. Select the 23.0.A.2.93 firmware and select to NOT wipe anything (see Picture 1). In the Exclude mark everything BUT system then start the flash process. If you do something wrong here you ran a VERY HIGH risk of bricking your device permanently

6. Put your device in flash mode (hold volume down and plug the device in) -> Wait until flash is finished and restart your device

7. Start your device - you'll notice black bars on the left and right of the picture

8. It should boot up and display lots of errors, but still function

9. Go into Settings -> Backup and Reset -> Factory data reset and make a factory reset from there (It seems wiping in flashtool does not work for some people)

10. Do initial configuration and select enable adb debug and allow mock location in developer options

11. Select Security -> Unknown Sources (If you do not do this, giefroot will not work)

12. Open a shell/command prompt and try if adb shell works and brings you to your device <- This step is important because here you authorize the device for adb access that you need later, please select to authorize the connected computer permanently when asked to do so

13. Open Flashtool and select flash. Then select flashmode and press OK

14 Select the 23.0.A.2.93 firmware and select to NOT wipe anything (see Picture 2). In the Exclude mark everything BUT kernel then start the flash process. If you do something wrong here you ran a VERY HIGH risk of bricking your device permanently

15. Put your device in flash mode (hold volume down and plug the device in) -> Wait until flash is finished and restart your device

16. Start your device and notice that the Screen stays pitch black, but you can hear the starting Sound

17. Once the tablet has started, go into the folder where you extracted giefroot and launch the install.bat

18. Wait till it is finished and tells you that you achived root (The device will reboot once while rooting, this is normal)

19. Open Flashtool and select flash. Then select flashmode and press OK

20. Select the SGP621_23.0.1.A.0.167_CE.ftf. Select to NOT wipe anything (see Picture 3). In the Exclude mark everything BUT kernel then start the flash process.

21. Put your device in flash mode (hold volume down and plug the device in) -> Wait until flash is finished and restart your device

22. Congratulation. After rebooting you should have a rooted SGP621 with the system of a D6603.

23. Now backup your TA with the tool from here

24. Unlock the bootloader via the instructions from Sony here. Do this only if you have your TA partition backed up!

To install CyanogenMod 12 nightly:

25. Download a CM12 nightly build from here.

26. Unpack the boot.img from the downloaded zip file

27. Go into fastboot mode (press volume up and plug device into computer until led flashes blue).

28. Issue 'fastboot flash boot /path/to/boot.img'

29. Issue 'fastboot reboot'

30. Once the led gets purple press volume down to get into recovery

31. Select install -> install via adb

32. Issue 'adb sideload /path/to/downloaded-zip.zip'

33. Wipe data and cache

34. Reboot and enjoy CyanogenMod

To install rooted Stock:

25. Open Flashtool and select flash. Then select flashmode and press OK

26. Select the SGP621_23.0.1.A.0.167_CE.ftf. Leave everything as it is and start the flash process.

27. Put your device in flash mode (hold volume down and plug the device in) -> Wait until flash is finished and restart your device

28. Get the advanced stock kernel from here, boot into fastboot mode, execute 'fastboot flash boot /path/to/the/Z3TC-stock-twrp.img'

29. Download RicDefeat from here.

30. Reboot the device and while booting once the led goes purple press the volume down key.

31. In the recovery tap on Advanced and Install with ADB and swipe to activate ADB

32. Issue 'adb sideload /path/to/RICDefeat.zip' (If sideloading does not work, put the zip file on your sd card and install it from there)

33. After that is finished, exit the recovery. It will ask you if you want to root. Answer yes and exit.

34. Open Flashtool again and select flash. Then select flashmode and press OK

35. Select the SGP621_23.0.1.A.0.167_CE.ftf. Select to NOT wipe anything (see Picture 3). In the Exclude mark everything BUT kernel then start the flash process.

36. Put your device in flash mode (hold volume down and plug the device in) -> Wait until flash is finished and restart your device

37. Restore your TA Backup and enjoy root on stock.

Congratulations, you now have a rooted device with either stock or CM12

Update Log

Update 1: I verified that Backup of TA works by reflashing it and checking if DRM is still intact in Service Menu.

Update 2: Changed instructions so wiping is done from the booted firmware directly, because for some users it was not possible to flash userdata from flashtool

Update 3: Added step 11 to enable Unknown Sources as otherwise giefroot will not work

Update 4: Added mirrors for the ftf files

Update 5: Added information to step 12 because it is important to authorize the device

Update 6: Added tutorial link

Update 7: Added tutorial for stock and CM12

Update 8: Update cause new giefroot is able to root our kernel

Thanks to zxz0O0 for giefroot and DevShaft for TA Backup

Good Luck and Have Fun