You know what a brick is in the Android world? No, well it is a device that is not functioning in any way, one that doesn't even turn-on. So, nobody likes to own a brick, specially not when it is a newly bought Galaxy S3. However, there are numerous ways that you'll find over at XDA Forums to unbrick your hard or soft bricked devices but what we'd like to see is a step by step guide officially by OEMs to unbrick a device. Well, fortunately one senior member at XDA has got his hands on the secret official bricked repair guide for the Galaxy S3.
This guide is the perfect novel for Android enthusiasts, specially the ones who own the Flagship device. This is the official guide that shows you how highly qualified Samsung tech support guys unbrick your precious Galaxy S3. It is a pretty straightforward but complex process that requires both software and hardware knowledge to perform, so you shouldn't be trying any of these steps if you're a newbie. Below are the main steps outlined in the guide.
– Brief JTAG process for GT-I9300
1) Copying JTAG(bootloader) file to external SD Card, using normal GT-I9300.
2) inserting the SD card to 'No Power' phone, and copy the bootloader file to the defective PBA.
3) After downloading bootloader file to the defective phone, enter the download mode with the phone, and download Full S/W.(PIT, PDA, CSC, PHONE files)
In a nutshell, this guide tells you how to put a bootloader on an external SD card, perform some hardware tricks and get your phone into download mode after that you will use Odin to flash the firmware and Voila! you've brought back your Galaxy S3 to life. So, if you have one bricked device laying around then you can surely try out these steps, at least it's better than having a $500 brick. Check out the Official Thread for more info and detailed steps.