Refresh a Samsung Core LTE

I’m a frequent tinkerer with my phone, and have rooted a Sony Xperia, Samsung Core, and some tablets.  The Samsung Core LTE is my current phone and it was time to give it a refresh.  In part, because during my tinkering, I ended up needing to do a factory reset.  As with previous posts, this one is intended to capture what happened, so I can this done more quickly in future.

First, I’m only dealing with an SM-G386W.  If that’s not what you have, then the files you’ll need will be different.  The phone had previously been rooted, but I’m not sure I ended up using the same approach.

Stock ROM and Factory Reset

The first thing was to grab the files I needed.  The SM-G386W is sometimes listed as a Galaxy Avant and this is how the stock ROM is listed at SamMobile.  A stock ROM means “just like the one your phone came with,” as opposed to a custom ROM, which isn’t.  The list is pretty lengthy, because each telecom installs its own custom bloatware apps.  I haven’t tried a different provider’s ROM, so I’m not sure what the experience would be.

This will download a .ZIP file, a compressed file that contains the image for your phone.  It’s worth pointing out here that, when you’re flashing files to your phone, you’re going to use two types.  One ends in .zip.  And the others don’t.  This can be confusing because sometimes you need to unzip the file and sometimes you don’t.  I think it’s accurate to say that:

  • if you start your phone in RECOVERY mode (volume up + home button, and press power), you install from a .zip file.
  • if you start your phone from DOWNLOAD mode (volume down + home button, and press power), you’re using a tool like Odin, and you need a file that doesn’t end in .zip.

In this case, once the SamMobile file has downloaded, I unzipped it and I had a file.tar.md5 file.  I restarted my phone in Download mode, started Odin (the file that enables flashing firmware to the phone), and I was ready to start.

Another point.  Older versions of Odin have a PDA button.  As of 3.10 or so, it’s become the AP button.   To flash the stock ROM:

  • Click the AP button and navigate to your tar.md5 file, the one you just unzipped
  • Odin will go through a process of verifying the file.  It will be short for small files, and much longer for full stock ROMs
  • When it is finished, start your phone (volume down, home, power) into Download mode
  • Connect your phone to your PC.  If you’re successful, Odin will say Added.  It took me 2 different USB cables before Odin was happy, so you may find that, if it doesn’t see your phone, you are using a cable that only charges, but doesn’t allow data transfer
  • Once Odin says your phone has been added, and you’ve selected your tar.md5 file, you can click Start.

Some sites suggest it matters what order you do these things.  It didn’t seem to matter for me whether I (a) started Odin first, (b) got to Download mode before connecting my phone to the PC, etc.  Odin won’t run if it doesn’t see your phone, and it won’t do anything if you haven’t selected a file.

If your attempt is successful, you get a nice PASS message.  Otherwise, FAIL.  One benefit of flashing the stock ROM is that it wipes out all the cache.  In previous attempts using custom ROMs on tablets, it was important to wipe the cache before restarting.  Otherwise you can end in a boot loop or soft brick situation that renders your device unusable.

You may also ask yourself why you need to do all this?  A factory reset sets the phone back to where it was but it leaves your phone in a custom state.  I decided that, in light of already running an older OS (4.4.2), it’d be nice to grab any recent updates.  Using the stock ROM will revert your phone back to official status.  Once you have flashed the stock ROM, go into your phone, under About Phone, and do a software update.  If your phone provider has responded to recent security issues, like this one, then you can patch your phone before you re-root it.

Recovery

The recovery option (volume up, home, power) is a powerful resource.  As I said before, you can use it to side load .zip files onto your phone.  Ideally you can replace the stock recovery with something like TWRP.  This makes ROM tweaks or other fixes much easier.  I attempted it with a TWRP that said it was for Core Prime LTE but the recovery kept failing.  I’d be interested if anyone can get a custom recovery onto the SM-G386W.

In my case, I mostly wanted to root the phone using Chainfire’s Super SU.  He has customized his file to work on loads of phones and appears to have automated updates.  Here are the G386W files listed, but I’d go back and grab the latest.  As you can see, there are a variety of file extensions to choose from, and an automated script to get you up and running.

  • I was unable to use Odin with any file other than the tar.md5 files.  I attempted to flash a .zip from recovery but it failed a signature check.  Apparently you can fix this if you have a custom recovery installed, but I didn’t.
  • If you don’t already have Odin, you can use the CF-Auto-Root script option at the bottom of the page.  The file you download, when you unzip it, will have Odin included.

Some people end up with a recovery.img or other file.  One Android user has created a tool to convert them to tar.md5.  I had mixed luck with this; I was better off starting with the correct file extension.  The process is the same as above.   When I restarted, the phone was rooted and I could start to add in some of the root-specific apps that I use.

David Whelan

I improve information access and lead information teams. My books on finding information and managing it and practicing law using cloud computing reflect my interest in information management, technology, law practice, and legal research. I've been a library director in Canada and the US, as well as directing the American Bar Association's Legal Technology Resource Center. I speak and write frequently on information, technology, law library, and law practice issues.