Wednesday, 7 August 2013

How to unroot your Galaxy S3 and flash it back to stock ROM

Rooting your phone and even trying out new ROMs is part and parcel of being a hardcore enthusiast. Ditching the corporate bloatware from phone network providers — the prime reason for rooting — is tantamount to ditching the corporate advertising and getting your phone back. But community ROMs don’t always match the hype, particularly when it comes to extracting your phone’s full features list.

It’s usually then that some decide they’d rather go back to what they had. If you’re running a Samsung Galaxy S2 or S3 phone and you’ve tried the latest CyanogenMod ROM, you might be missing the ability to connect your phone to your TV, for example.
So the big question is: can you put your phone back to the way it originally was?

Yes, you can go back

It’s easy to get a bit caught up in the advanced nature of rooting and flashing your phone, and see it all as a bit of a dark art. But if you remember your phone is just a portable Linux computer, changing ROMs becomes changing the OS and it suddenly seems less daunting.
The best rule of thumb for changing a ROM in your phone is to always be methodical in what you do, never panic and give your phone time to do what it needs to do.
In very simple terms, bringing your phone back to original condition is all but the same as putting a new ROM on it — because that’s exactly what you’re doing. However, there are several ways to do it, depending on where your starting point is.

Danger, Will Robinson!

Flashing your phone will null and void your warranty. While we have successfully tested the processes described in this story, we offer no support or guarantee. You try them at your own risk.

First things first: Back up everything

It should become as second nature as breathing — any time you change your phone’s ROM, back up everything. Storage is cheap; getting data back that you haven’t backed up isn’t. We use two methods. First, we use the ‘Recovery Mode’ Nandroid backup to make a complete backup of the phone, which is basically a snapshot of the phone as it is. Second, we use combinations of Android apps to back up the phone — we sync email, contacts and calendar with Google Sync and back up SMSs with SMS Backup and Restore.
We don’t normally back up apps as they can be restored from Google Play. We’ve never had much luck restoring apps when changing from one OS to another — not surprising, really. You probably already know how much Windows likes to be copied from one computer to another. Anyway, the general idea is to back up everything and copy the backup files to your PC — don’t leave them on your phone.

Method #1: Nandroid backup

If you were a good APC reader and performed a Nandroid backup before you flashed the new ROM, you can just back up your personal data (email, SMS and so on) and restore that Nandroid backup. The downside is, you’ll be sending your phone back in time to the point you made the backup, as everything after that date will disappear from your phone until you reinstall them from your new backups. This method basically returns your phone to its previous ROM.

Method #2: Install a new stock ROM

If you forgot to do a Nandroid backup or it hasn’t worked, all isn’t lost. Another option would be to take the latest available stock ROM from your phone’s manufacturer or your network provider and install that onto your phone. The downside here is that most stock ROMs are a generation (or possibly two) behind the latest available release. For example, Optus just released its Android 4.1.2 ROM for the Galaxy S2 in late March, despite 4.2.2 now being the latest benchmark.

Where to get your ROM

Samsung is like most phone makers, preferring to deliver new ROMs as over-the-air (OTA) updates rather than as a downloadable file you install yourself. However, if you’ve installed a non-stock ROM, the ability to get updates OTA will likely have been removed. So where can you download stock ROMs? For Samsung owners, head to Sammobile. It’s the most complete list of stock ROMs by phone provider we’ve seen for any smartphone, let alone just Samsung mobiles.

Which ROMs?

If you’re going to get into the habit of flashing ROMs onto your phone, we think it’s always a good idea to understand exactly what you’re doing. And when it comes to phone ROMs, there’s more than meets the eye.
When you load a new OS onto your PC, you’re installing high-level code that interacts directly with the user. It contains the code that runs your apps and provides the basic apps like Windows Explorer and so on.
In your phone, the equivalent is colloquially referred to as the Phone ROM. It’s the high-level Android operating system you interact with. But it’s not the only ROM your phone uses.
Your PC’s motherboard has a low-level firmware called the BIOS (basic input/output system), a code set that communicates between the hardware and the operating system, like talking to hard drives and setting the CPU clock speed. Your phone’s equivalent here is commonly called the Radio ROM and its function is to handle the wireless hardware electronics in your phone. However, just to be different, Samsung uses different terms:
  • PDA. This refers to the Android operating system ROM version code, although it doesn’t obliquely refer to Android in any way (just to make it easier… not).
  • Phone. What everyone else calls the Radio ROM is Samsung’s Phone ROM, handling the modem and wireless connectivity electronics.
  • CSC. This stands for Consumer Software Customisation. It’s a ROM separate to the PDA ROM, which contains the corporate bloatware specific to your network provider and your geographic location.
We’ll talk more about these later, but for now, it’s just enough to understand what these Samsung terms mean and how they correlate to terms you’ll read online.

Picking the right ROM

As we’ve mentioned previously, the most important aspect of picking a stock ROM is making sure you get the right one for your phone model. If you have the standard 3G version of the Galaxy S3 as sold in Australia, its model number should be GT-I9300T (you can find it on the Samsung splash screen when your phone first boots). The international version is known as the GT-I9300, while the 4G version is the GT-I9305. And when you head over to Sammobile, these are the model numbers you need to look up your model.
The reason it’s so important that you pick up the right download is because Samsung stock ROM packages include both the PDA and Phone ROMs (the operating system and the Radio ROMs). So while a PDA ROM for another phone might work, a different Phone/Radio ROM probably won’t and will very likely brick your Galaxy.

Beware the bugs

The other thing you need to be careful of is making sure that you don’t choose too old a ROM. For example, if you’re running a Galaxy S2, don’t choose an Android 4.0.4-based ROM, otherwise you could end up bricking your phone through the Galaxy S2 Superbrick Bug. The S3 isn’t immune either, with its own Sudden Death bug plaguing Android 4.0.4 ROMs. Unfortunately, it means we can’t just tell you to get the latest ROM and you’ll be right — you should try to keep up with phone trends, particularly your model, and be aware of what’s happening in the market.
In the case of the Galaxy S2 and S3 phones, new Android 4.1.x-based ROMs have so far proven to be bug-free and should be your starting point for stock ROMs.

How to get it onto your phone

ROM flashing has become so sophisticated that there are three different options available for flashing a Samsung phone.
  • Recovery Mode. You copy the ROM file onto your phone’s storage and use the phone’s built-in ‘Recovery Mode’ to install it.
  • Samsung Kies. Allow Samsung’s official software to detect the phone and grab the latest official phone/network update and install it.
  • Samsung ODIN. Grab the ROM and install it yourself via your PC.
Our preference is to use the ‘Recovery Mode’ or ODIN — we’re just not fans of Kies. It worked happily enough with our test Galaxy S3, but it’s never picked up OTA updates with our S2. That said, it’s a consumer-focused tool so it’s not designed to let you get too funky with your phone. ODIN is reportedly a leaked internal Samsung app and potentially more dangerous (because it lets you do dangerous things like repartition flash storage), but if you don’t stray too far, it’s easy to use and very effective.

How many times can I flash my phone?

The NAND flash storage inside your phone can support many hundreds of write cycles so it’s unlikely you’ll kill your phone’s storage by flashing a new ROM. The bigger issue comes if you flash a new Radio ROM (the code that talks to the phone’s wireless connectivity electronics). Flash a dud Radio ROM and you may well brick the phone. While no-one can give you an iron-clad guarantee, chances are you’ll have a new phone before you reach your phone storage’s flash write limit.

Warranty restored?

In the old days with phones like the HTC Desire, restoring a rooted phone back to its original condition with a legitimate stock ROM effectively also restored your phone’s warranty — mainly because there was no way for the phone provider to tell whether the phone had ever been rooted or ROM’d in the past.
However, the Galaxy S2 and S3 now have a built-in custom binary download counter that records how many times the phone’s storage has been flashed. The idea was that even if you replaced a community ROM with an official one, Samsung would still know you’d flashed it in the past, thanks to that counter, if the phone was ever presented for repairs under warranty.
So the reality here is that restoring your phone to stock doesn’t restore your warranty if the flash counter has it registered that you’ve flashed a different ROM at some point.

Turning back the clock

Winding back the old mechanical odometer in cars was one of the dodgier practices rogue used car sellers would use on unsuspecting buyers and make clapped-out motors seem like they’d literally lived a sheltered life. Well, it’s also possible to wind back (as in reset) the binary download counter; however, we don’t recommend it.
There’s an app on Google Play by the ever-brilliant Xda Developer/moderator Chainfire called Triangle Away, which attempts to reset the counter. But because it operates on the phone’s bootloader code that tells the phone what to launch when it first boots, Triangle Away may brick your phone if it doesn’t work correctly — not a recoverable brick like an Android ROM flash gone wrong, but a fully unrecoverable brick that requires advanced electronics knowledge (JTAG) or a new board to fix.
If you’re seriously worried about warranty, don’t flash your phone in the first place. Otherwise, if you’re happy to lose your warranty, there’s nothing to be gained by resetting the counter, although there’s plenty more to lose.

You choose

In the end, it’s your phone — you get to choose which ROMs you install. While most community ROMs are generally fantastic at removing bloatware, they don’t always give you your phone’s full features list and a stock ROM, warts and all, might actually be a better option. There are some good ROMs based on official releases that maintain functionality, but if you want to go back to being safe and conservative, a stock ROM is the way to go.

Step-by-step guide: Install a stock ROM on a Galaxy S3 using ODIN

WARNING: While this guide was successfully tested on a Samsung Galaxy S3, we provide no support or warranty on the information provided. Use at your own risk.

Step 1:

Charge up your phone to at least 75% capacity. Make backups of your current phone setup using Nandroid (complete phone backup), Google Sync (email, contacts, calendar) and SMS Backup and Restore (SMS). If you haven’t already, install Samsung Kies for its USB drivers — we won’t be using this software otherwise.

Step 2:

Head to Sammobile, search for your phone model and select the version that matches your location and network provider. Once downloaded, unzip the contents into a folder on your hard drive. Be warned: S3 stock ROMs can be greater than 1GB in size and require up to 2GB to unzip. You should see a large ‘tar.md5’ archive file after unzipping.

Step 3:

Download the Samsung ODIN 1.85 tool from (size: 204kb). Unzip it, launch it and with the phone turned off, plug your S3 into your PC’s USB port.

Step 4:

Turn the phone on into ‘Download Mode’ (press and hold the power, ‘Home’ and volume down buttons until you see the warning screen). You should see the phone listed in ODIN. Press the ‘PDA’ button and select the ‘tar.md5’ archive. Ensure the ‘Re-Partition’ box is unticked.

Step 5:

Press the ‘Start’ button and allow ODIN to flash your phone with the stock ROM. It’ll take a few minutes but once it’s completed, you should get the big green ‘PASS’ signage. Your phone should now automatically reboot.


If your phone keeps showing the Samsung splash screen and rebooting, it’s stuck in a boot loop. Don’t panic — it’s a common issue. Provided that you got the green ‘PASS’ sign in step 5, here’s what you can do to fix it.

Step 6:

Pull the cover off your phone and remove the battery. Put it back in when the screen goes blank, put the cover back on and boot your phone into ‘Recovery Mode’ (press the power, ‘Home’ and volume up buttons until you see the Samsung splash screen). When the recovery menu appears, navigate using the volume buttons to ‘Wipe data/factory reset’ and press the power button to activate.

Step 7:

When it’s done, navigate back to ‘Reboot Now’ and allow the phone to reboot. It should now come up as normal.

Will a stock ROM keep my phone rooted?

The short answer is no. By installing a stock ROM, you also remove the root access because you’re no longer using the same operating system. Think of it as if you were replacing Windows XP with Windows 8 — you don’t have the same OS installed so none of the same conditions remain. However, there’s nothing stopping you from rooting your phone again with the new stock ROM installed if that’s what you want. (Just follow the process in our article here on How to root your Android phone).

Other tips

  • If the flash process failed, check if it passed the MD5 check test — this checks to see if the download is a valid file. If it failed, download it again.
  • If the MD5 checksum test is fine, try flashing it again.
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