Update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean Custom Firmware

T-Mobile Galaxy S3 SGH-T999 can now be updated to Android 4.1.2 Jelly Bean custom ROM. This ROM is based on CyanogenMod 10 (CM10) and is very stable enough to be used on your phone. This custom ROM will allow you to experience AOSP Android 4.1.2 with stock features and some extra features and customizations at system level. You can update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean custom firmware using the tutorial below.

As you continue reading below, we will guide you through the entire process of how to install Android 4.1.2 CM10 Jelly Bean on T-Mobile Galaxy S3 SGH-T999 with complete steps. Please make sure you backup all your data as given below because this tutorial will wipe your data. Remember, this is a custom ROM, not an officialfirmware update by Samsung. Let’s get to the tutorial now.

Disclaimer: All the tools, mods or ROMs mentioned below belong to their respective owners/developers. We (TeamAndroid.com) or the developers are not to be held responsible if you damage or brick your device. We don’t have you on gun point to try out this tutorial.

Make sure you have installed all your USB drivers for the Samsung Galaxy S III to connect it with the computer. Download Samsung T-Mobile Galaxy S3 USB drivers! Apart from just the USB drivers, there are a few more things that you need to take care of.

1. You need to enable USB debugging mode. This helps to connect your Android phone with the PC.

2. Your phone battery should be 80-85% charged. If your phone goes off suddenly because of battery, during flashing ROMs or installing mods and updates — your phone might go dead permanently. 

3. Backup all your important data that you might need as soon as your flash a new ROM, or make a backup for just in case, you never know when anything might go wrong. See below on how to backup data.

Now, let’s proceed with the tutorial on the next page and update T-Mobile Galaxy S3 SGH-T999 to Android 4.1.2 CM10 Jelly Bean custom firmware.

instructions guide on how to installAndroid 4.1.2 CM10 Jelly Bean custom firmware on T-Mobile Galaxy S3 SGH-T999. If you are used to installing custom ROMs on your T-Mobile Galaxy S3 SGH-T999, then this should not be any different for you.

However, for beginners, you need to root your Samsung T-Mobile Galaxy S3 and install a custom recovery. Please Google that up if you are unsure and make sure you read the tutorial once before actually performing it on your device.

To Remember:

• This tutorial is only for installing Android 4.1.2 CM10 Jelly Bean on Samsung T-Mobile Galaxy S3 SGH-T999. Please do not try on any other Galaxy S III variants.
• Your phone should be rooted and have ClockworkMod recovery installed from before.
• This tutorial will wipe out all your data. Proceed at your own risk.
• Perform a Dalvik Cache wipe before proceeding from the recovery mode.
• Samsung KIES will NOT detect your phone after installing this ROM because it is a custom firmware.
• Make sure you backup all your data in your phone before proceeding.

Complete Step-By-Step Instructions:

Step 1 - Download Android 4.1.2 CM10 Jelly Bean ROM and Google Apps for Galaxy S III to your computer.

Step 2 - Connect and mount your T-Mobile Galaxy S3 USB memory on your computer using the USB cable.

Step 3 - Now copy/paste the downloaded Android 4.1.2 ROM zip and Google Apps files to your SD card. Make sure the files are in the SD card root (not in any folder).

Step 4 - Then turn OFF your phone and disconnect from the USB cable.

Step 5 - Now to get in the Recovery Mode. Switch ON the phone while pressing and holding Volume Up + Home + Power buttons together.

Step 6 - In ClockworkMod recovery, perform a full data wipe first. Then scroll down to “flash zip from SD card” and press the Power button to select it.

Step 7 - Press the Power button again and select “choose zip from sdcard”.

Step 8 -Now using your volume keys, navigate to the Android 4.1.2 ROM zip file that you copied to your SD card and select it using the Power button. Confirm theinstallation on the next screen and the installation procedure should start now.

NOTE: Repeat this step for the Google Apps zip file as well.

Step 9 - After the installation completes, go to “+++++Go Back” and reboot the phone by selecting “reboot system now” from the recovery menu. The phone will boot now and it might take about 5 minutes to boot on your first time. So, please wait.

That’s it! Your T-Mobile Galaxy S3 should now have Android 4.1.2 CM10 Jelly Beancustom ROM installed on your phone! Go to Settings > About phone to verify.

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