Tools :
1. Driver:
http://lenovo-forums.ru/Files/OS/A390/MTK65xx_Driver.zip
2. Flash Tool:
http://lenovo-forums.ru/Files/OS/A390/SP_Flash_Tool_v3.1224.01.zip
3. Recovery:
http://lenovo-forums.ru/Files/OS/A390/Custom/TWRP_v2.4.4.0_A390_S312.zip
How Recovery for
Step 1: unzip the downloaded file (TWRP_v2.4.4.0_A390_S312.zip)
Step 2: To install the drivers for the computer..Turn off the phone, connected to the computer, the computer will notify the Preloader MT6577 driver installation,unzip the folder above driver in the extracted folder run the InstallDriver.exe. After the driver installation is complete you disconnect the device.
Step 3: Open the folder Flash_tool software Flash, click the scatter-loading, choose MT6577_Android_scatter ... recovery in just unzip the folder, click OK. Click the Recovery button below if it is not built (and built by default).
Step 4: Click on the word Download on ... you will see a dialogue you choose'' yes'' and quickly plugged into the usb and it will automatically load the file recovery on your machine (the phone must be off)
- After plugging the phone into the flash-tool will show the power status bar red to yellow then wait for the message "ok" green is successful .... then disconnect the phone and you have recovery
Step 5: You remove the phone battery cover to reach the 30s and then you press the Power key combination and volum + key until the phone boot into Recovery mode, then let go ... This time will be delivered Team Win Recovery.. You now have TW recovery you can now root your device. (Make nandroid backup first before rooting you phone)
Rooting:
After boot in recovery i remember it will ask you to install superSU just drag/swipe to install..
NOTE: Internet connection required when rooting because when you open the superSU after reboot it will ask you to download the full root file i think. xD.. and pressed down by TW flashed.. and i forgot whats next..
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Video Tutorial
http://youtu.be/lrWQkyOv18E
for full detail refer & credit to this link:
http://www.tinhte.vn/threads/lenovo-a390-huong-dan-recovery-va-root-tim-kiem-rom.2094772