How to Fix/Unbrick or Recover Bricked AT&T Galaxy S3 SGH-I747

Here's a solution to recover your bricked AT&T Samsung Galaxy S III SGH-I747 phone for some reasons that you messed up from flashing wrong ROM, bootloader image from the GSM variants like the Galaxy S3 GT-I9300 (International)  which is not compatible with Galaxy S3 SGH-I747 (AT&T). It was also bricked by rooting because you installed with a wrong root kernel. Those are just the most common issues why the heck you screwed up and brick your Samsung Galaxy S3 phone in no time.

Symptoms of bricked Samsung Galaxy S3 (AT&T SGH-I747)
1. The phone boot and shows the Samsung screen for a split second and then it automatically turns off.
2.  It won't  Power ON but it just shows the odin download screen with yellow triangle and firmware update warning.
3. The phone keeps on restarting (with vibrations) after the Samsung logo appears.
4. The phone is totally dead, unresponsive or no visible signs of life.

Does a bricked Samsung Galaxy S3 (AT&T SGH-I747) can be fix or recover back to normal?
Yes and NO, there are two types of bricks - the softbrick and hardbrick.
The Softbrick can be recovered if you can still access your Galaxy S3 Download Mode screen (Pressing VOLUME Down + HOME + POWER button). If you can't access the download mode, then you can't recover it by yourself anymore.

Hardbricks refers to the phone as totally jammed, it doesn't show anything, can't access the download mode screen. The only solution for this is by called JTAG flashing, which is forcing to install the firmware back to the phone. The process is not too easy, this includes disassembling the phone, some soldering required and flashing by means of using a flashing device tool.

If you can still access the phone into download mode, then try this method below, this might help you to restore it back to normal. But the best method to have your Galaxy S3 back to life if you can't recover it anymore with yourself is to bring it back to your dealer. Explain something  that might encourage them to have your phone fix or have an exchange for warranty.

Flashing bricked Samsung Galaxy S3 (AT&T SGH-I747) with original stock Boot Image
This solution may fix your phone if you have flash a wrong bootloader image from Samsung galaxy S3 GT-I9300 (International GSM)

Grab the boot image file odin flasher and USB driver
boot-stock-att-sgh-i747.tar
Odin flasher - Odin3_v3.07
USB Driver -  Samsung Android USB Driver

Use PC with Windows OS (Odin will not work on Mac and Linux OSX)
Recharge your battery using external battery charger since you can't charge the battery in the phone.

1. Run Odin on your PC desktop
2. Boot the Galaxy S3 into download mode screen for Odin.
Turn it off, once completely shut down  hold down the 'HOME' + 'VOLUME DOWN' buttons and press the 'POWER' button for about 2 seconds until a WARNING! Screen appears. Press the 'VOLUME UP' button to continue or enter Download Mode.
3. Connect the phone to PC via USB. Then make sure you can see as phone "Added" in Odin log box or highlight the COM:ID once the device is detected,
4. In Odin window, DO Not tick 'RE-Partition'  only Tick 'Auto Reboot' and 'F. Reset Time' and nothing else.
5. Now load the boot image and Odin on the PDA button.
6. Click on "Start" to flash the image.
7. The phone will then reboot to normal mode then you're lucky.

If the problem still persists, refer to the below method.

Flashing Samsung Galaxy S3 (AT&T SGH-I747) with original stock ROM or Firmware
Grab one of the original Stock Firmware

IMPORTANT NOTE: If you bricked in 4.4.2 and 4.3 this guide will not work for you, since this post covers long before the 4.3 and 4.4.2 update took placed.  Read this guide at XD-developers that might help you recover your phone http://forum.xda-developers.com/showthread.php?t=2549068
ATT_I747UCUEMJB_I747ATTEMJB (Dec 2013, 4.3 JB)
ATT_I747UCDLK3_I747ATTDLK3 (Dec 2012, 4.1.1 JB)
ATT_I747UCALG1_I747ATTALG1 (July 2012, 4.0.4 ICS)
ATT_I747UCALEM_I747ATTALEM (May 2012, 4.0.4 ICS)

Again make sure the battery is fully charge (recharge the battery using external battery charger)
1. Run Odin on your PC desktop
2. Boot the Galaxy S3 into download mode screen for Odin.
Turn it off, once completely shut down  hold down the 'HOME' + 'VOLUME DOWN' buttons and press the 'POWER' button for about 2 seconds until a WARNING! Screen appears. Press the 'VOLUME UP' button to continue or enter Download Mode.
3. Connect the phone to PC via USB. Then make sure you can see as phone "Added" in Odin log box or highlight the COM:ID once the device is detected,
4. In Odin window, DO Not tick 'RE-Partition'  only Tick 'Auto Reboot' and 'F. Reset Time' and nothing else.
5. Now load the tar file e.g "I747UCUEMJB_I747ATTEMJB_I747UCUEMJB.tar.md5"  in Odin PDA button.
6. Click on "Start" to flash the stock firmware
7. Wait until the flashing successfully finishes, you'll just see a word 'PASS' in odin once completed.

If the phone reboot normally, its then a success story, and if not, there's nothing I can do to add more but just recommend  you to contact or visit your nearest service center.

How to Avoid bricking your Galaxy S3
Don't Flash other variants Stock ROM and kernels. (If you find any instruction on the web or forum read it carefully or ask something that you don't understand)
Don't use root kernels and boot images, from custom ROM builds for GSM or GT-I9300

Credits to Mark aka MSKIP (highly recognized developer) for the Boot Image
Original thread: http://forum.xda-developers.com/showthread.php?t=1727443