First, download the stock 4.1.2 Jellybean Full distribution,
I777UCMD8 from the Download Repository. It's the next to last item near the bottom. The downloaded file is in seven-zip (.7z) format and you need to extract the contents using an archiving program. The resulting file, which will have a ...tar.md5 extension, is the file you will use in step 7 below. Also download Odin3 v1.85. There is a link near the top of the page in the Repository.
How to use stand-alone Odin3 to flash firmware:
Follow and recheck each of the following steps. Do them in order listed, as some steps are dependent on previous steps. Instructions are for Odin3 v1.85. It should work with any version of Odin, but some details, like color of items, may be different.
1.) Open Odin on the Windows Desktop.
2.) Have the USB cable plugged into USB port on the computer, but *Not* plugged in to the phone.
3.) Shut the phone off.
4.) While holding down the vol+ & vol- keys, plug micro-usb plug into phone.
5.) In Odin, you should get the yellow box under where it says ID:COM with the text 0:[COMx], and in the Message area, <ID:0/00x> Added!! where x is some number, usually 1-8.
6.) In Odin, make sure Auto Reboot and F. Reset Time are checked and all other items are not checked.
7.) Click on the PDA button. Browse to the tar file you want to install and select it so its path appears in the text edit box next to the button.
8.) Make sure the check box next to the PDA button is checked.
9.) Click the Start button.
10.) You should see the green progress bar advancing.
11.) When complete, you will get a PASS (or FAIL if unsuccessful).
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Once you have the phone up and running, Framaroot with the Aragorn exploit is the easiest way to root.