[Xperia Tablet Z General] Magnus_E:
The objective of this post is to explain how to currently install a custom ROM in our device. (for total newbies like me, you can also refer -among others- to my previous post). I give the general procedure which wipes everything in your device, but you can check various precious posts in xda that variate this procedure.

The codename for our device is "pollux_windy", which is the Wifi-only version. The LTE version (I should probably get the LTE!) is "pollux" and I suppose the general procedure (with the corresponding firmwares to your specific device) will work for any Xperia device. You can also get the general idea from this post.

As a general rule of thumb do not forget after/before every firmware flashing to:

Enable developer mode (explained here)

Enable the USB Debugging mode (explained here)

Trust installation from unknown sources (explained here)

Steps.

A. Unlock the bootloader.

You can refer here and then check that it is successfully unlocked with these steps (taken from here ):

Open the Contacts app.

Click the menu button.

Click Settings.

Long press (for about 5 seconds) somewhere in the empty space just above status bar, as indicated by the red frame in the screenshot below, and then release your finger. A button named Enter service code will then appear in the same area (this may take a few tries).

Click Enter service code. A dialler will appear.

Dial *#*#7378423#*#* . Then go to -> "Service Info" -> "Configuration". If there is:

Bootloader unlock allowed - Yes << this means that your Bootloader is Locked

Bootloader Unlocked - Yes << this means that your bootloader is unlocked

B. Flash a firmware in which you will root the device

Download/install FlashTool.

Download and place to the FlashTool's folder "firmwares" the firmware "SGP312_10.5.A.0.230_VMo UK_IE.ftf". More information here . In sort, download and extract http://d-h.st/MrI and http://d-h.st/ULc

Open FlashTool and connect the powered-off device (USB cable) in Flashmode, holding the Volume Down button while you plugin the usb cable. The FlashTool should say that it is connected in Flashmode. Then flash the 10.5.A.0.230 firmware in it.

C. Gain root to the new firmware

Open the device, complete the setup wizard and connect to a wireless network. You do not have to setup the Google Account since you can download every application googling the respective APK files, but Google Play is easier to use.

Get (click λ) the towelroot APK, install it and run it (click "make it rain"). You should have root, which you can check with a Root Cheker like this one.

Download/Install SuperSU APK (this is actively developed, while SuperUser is abandoned at the moment) as described here.

D. Install a Recovery to easily flash new ROMs

NUT has done excellent work with XZDualRecovery.Follow the instructions for installing it in his thread. In short:

Download the installer, run it and follow its instructions.

Select SuperSU and of course grant access to your computer from your tablet (watch the tablet screen).

E. Download a Custom ROM and Google Apps

I had problems with Cyanogenmod (versions 11 and 12) that I cannot explain. I had no GPS and no media sound from the speakers, but I did have "notifications" sound! I could listen to "media" sounds using headphones, though. So I tried the nightly OmniROM which seems very stable and fast at the moment, with no sound problems and also has a working GPS! You can get it directly from their site (the NIGHTLY I downloaded is omni-4.4.4-20150223-pollux_windy-NIGHTLY.zip which runs just fine). Somewhere I read that PacMan ROM - also works perfectly but I have not tested it yet.

I had device recognition problems from the Recoveries ("Status 7 Error") that I think dear NUT will solve promptly. What I did to solve them is

Upack the ROM zip.

Remove the first line (from assert(...); till the column) of META_INF/com/google/android/updater-script and save the file.

repack the ROM to a zip.

Then copy this zip to your external SD card. If you need google apps (you probably do, to use Google Play instead of other applications like Aptoide), you will also need to download and place to your external SD card the corresponding google apps from here - (I found it in this post - which also explains the different gapps versions)

F. Install the Custom ROM

So now that both the ROM and (optionally) gapps are in the device's SD card:

Enter the Recovery while repeatedly pressing Volume Up or Down while the device boots.

Wipe everything (except the external SD card, obviously --- if you delete the zip files by mistake you must begin again from step B. using the FlashTool to flash the *.230* ftf).

Reboot and setup/enjoy your new ROM.

It seemed that with OmniROM I had lost root access so I had to reinstall SuperSU. I did this by downloading the flashable/installable zip - and flashing/installing it through the recovery.

In the end a did a full backup with the TWRP recovery and one with Titanium backup