Originally Posted by penky had
Xperia Z c6602, andoid 4.4.2 10.5.a.0.230 baseband 9x15a-acefwmazq-30110089-64 kernel ver.3.4.0-g32ce45a
You can download kitkat stock firmware for 6602 from here
Download flashtool to flash firmware from here
How to flash instructions are given below
Download and install the Flashtool
Go to the flashtool folder in c drive, keep the firmware ie the ftf file in the firmware folder of flashtool
Next go to where you installed flashtool folder in C drive and then to the drivers folder.
Run the Flashtool-drivers.exe file.
Xperia Z drivers, flashmode drivers and fastboot drivers.
Accept all the prompts and once finished load flashtool
Click the thunder button on top left
Now select flashmode
Select the firmware you want to flash
Turn off phone(Hold power and both the volume keys till you feel 3 vibrations)
When it tells you to connect hold down the volume button and connect usb to phone
Flashing will start
After flashing is complete boot the phone