If you have rooted your phone and tried out various ROMs, it is possible to “unroot’’ your phone and go back to the stock ROM. You might want to do this if you need to get your phone serviced, or if you want to sell you phone on eBay or Swappa.
Here is an overview of the process:
- Back up whatever you need from your phone
- Optional: Reset the flash counter using Triangle Away
- Locate and download the stock ROM for your phone
- Install the stock ROM using Odin
Warning – you can brick your phone if you’re not careful (or really unlucky). This guide is intended for people who are comfortable with the risks involved.
1. Back up whatever you need from your phone
2. Optional: Reset the flash counter using Triangle Away
Most Samsung phones have a counter which tracks the number of times the phone has been flashed with a custom ROM. Triangle Away is an app on Google Play that attempts to reset the counter. This makes it difficult to detect that the phone has ever had a custom ROM installed, which is potentially helpful for warranty purposes, or prior to selling a phone.
If interested, make sure you read this XDA post in order to understand the risks involved.
3. Locate and download the stock ROM
Samsung ROMs can be downloaded from here: Sammobile. It requires a free account, which is probably worth setting up, since this is generally recognized as the best source for stock Samsung ROMs.
If you don’t want to create an account, here is another source: http://forum.xda-developers.com/showthread.php?t=1968625
Once downloaded, extract the contents of the zip file into a temporary directory. You should have a large (~1GB or more) file ending in .tar.md5.
4. Install the stock ROM using Odin
Odin is a Windows program from Samsung that you will use to flash the stock ROM onto your phone. Typically, Odin is used only for official stock Samsung ROMs, which are distributed as .tar files. Custom ROMs have a .zip format, and are not flashable by Odin.
If you don’t already have it, download Odin from the following thread on XDA: http://forum.xda-developers.com/showthread.php?t=2189539. Make sure you get the correct version. For the Galaxy S3, the proper version is 1.85.
Once you have Odin, start it up, and then put the phone into Download mode. You can do this either from the reboot menu in recovery, or by powering the phone off, then press and hold the Power, ‘Home’ and Volume-down buttons until you see the Downloading… screen
At this point, you should see a COM port listed in a box under the ID:COM heading.
Press the ‘PDA’ button and select the tar.md5 archive. Make sure the ‘Re-Partition’ box is NOT checked.
Press the Start button and Odin will flash your phone with the stock ROM. After a few minutes, you should get a ‘PASS’ message, and then your phone will automatically reboot.