I was getting fail errors on the stock tar.md5 from samsung through odin in download mode it just would not take, I tried 4 different computers, different cables, different usb ports...
The following is how I got mine to be back up and running properly:
You will need 2 files which I will provide a spam free link to and a little bit of time..
Odin 3.09 link
Firmware for 900A link
Download the above files
extract the files
you will end up with 4 files
boot your phone into download mode
Hold volume down
hold home button
press power button
then hit volume up to continue
Now connect your phone to the pc
extract and open odin
Open odin 3.09
if it detects your phone it will show a com port lit up now you are good to go.
in odin 3.09
make sure auto reboot is checked
and F.reset Time
NO NEED FOR THE BL file at this time with our locked bootloader[B]in the bl tab Leave blank
Do not load the bl file as of yet we have a locked bootloader and it wont flash
pick the ap and then the ap file you downloaded
pick the cp tab and the cp file
then the same for the csc file
make sure all tabs are checked
the AP file will take over a minute to load dont get nervous odin has to load it into itself..
once all 3 are in their respective tabs and checked click start and that is it
in about 6 minutes you will boot back up to a stock galaxy s5 for att