Galaxy S3 GT I9300
Samsung Galaxy GT I9300 gets Android 4.1.2. Photo: Google Google

Samsung Galaxy GT I9300 is among the first batch of Android devices to get the latest Jelly Bean update - Android 4.1.2 - through stable builds of custom ROM. Earlier, the same update was released for Google Nexus 7, which is officially the first device to receive the new Jelly Bean update.

Meanwhile, there is still no word on the release of official firmware for Android 4.1.2 from Samsung. Due to the Root Box team and XDA recognised contributor bajee11, Galaxy S3 I9300 users can now install their favourite custom apps and tweaks for the latest Jelly Bean OS on their phones, without having to wait for the official release.


  • The Root Box ROM and the instructions given in this guide are applicable for the international version Galaxy S3 I9300 model only and will not work with any other device. Verify the device's model number by navigating to Settings > About phone.
  • Developers, however, recommend users to backup apps, important personal data and settings to avoid loss of data while installing the Root Box ROM-based Android 4.1.2 Jelly Bean update.
  • Ensure that your Galaxy S3 device is rooted by downloading and installing Root Checker app from the Google Play Store. Continue with the instructions given in this guide, if the device is not rooted.
  • Once the phone is rooted, download and install the ROM Manager app from the Google Play Store.
  • Verify that the phone's battery is at least 85 percent charged to prevent unexpected device shutdown while flashing the custom ROM or installing the Android 4.1.2 Jelly Bean update.
  • Enable USB debugging mode by navigating to Settings > Applications > Development and check the USB debugging option. This feature helps in connecting the phone with the computer.
  • Ensure that there is at least 1GB of free space on the phone's external SD card to accommodate the custom ROM installation on it.
  • Disable or uninstall all antivirus and security suites on the smartphone to prevent unwanted system conflicts during the installation of firmware update.
  • The instructions provided in this guide are meant for reference purpose only and do not cover any warranty claims involving device damage or issues arising out of using the Root Box firmware update. Users are cautioned to proceed at their own risk.

Root Box Android 4.1.2 Jelly Bean Features

  • Based on JB 4.1.2 - Built from RootBox Sources (Teamhacksung, CM & AOKP)
  • HSPA+ Support
  • A2DP Support
  • T9 Dialer
  • Cherry picked fixes from CM
  • OTA Update
  • ExTweaks integrated in Settings - if ExTweaks installed in /system/app
  • Init.d Support
  • AOKP Features

How to Update Galaxy S3 GT I9300 to Android 4.1.2 Jelly Bean with Root Box ROM

  • Download the Root Box Based Android 4.1.2 Jellybean Custom ROM and Google APPS Package from here to your computer. After the download completes, connect your phone to the computer with an USB cable and copy the two downloaded zipfiles to the root folder of the phone's SD card.
  • Disconnect the phone from computer. Then, power off the Galaxy S3 device and boot into the recovery mode. To do so, press and hold the Volume Up and Home key buttons and keep tapping the Power button until the device boots into recovery mode.
  • In recovery mode, choose Wipe data/factory reset and Wipe Cache partition options. If thedevice accidentally boots into normal mode, then you need to retry the process by repeating the previous step. You can also enter the device in recovery mode using the ROM Manager app.
  • Choose install zip from sd card and click choose zip from sd card. Now, browse and select the Root Box Jellybean 4.1.2 Custom ROM and Google Apps Package which you copied to your phone. It will take about 4 to 5 minutes for installing the update.
  • After the ROM is installed, hit Go Back and tap Reboot System now to reboot the phone in the normal mode. The first boot is more time consuming than the normal mode, as it has to finalize all the apps. So, leave it alone.

Note: If the device locks in boot loop sequence or gets stuck at the welcome screen, just reinsert the battery and repeat the above instructions to complete the ROM installation.

Root Box ROM Based Android 4.1.2 Jelly Bean update is now successfully installed on your Galaxy S3 GT I9300. Navigate to Settings > About phone to verify the firmware version installed.

[Source: Android Advices]