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[–] foxlet 0 points 1 points (+1|-0) ago  (edited ago)

Ah, downgrades on a locked firmware phone are almost never suggested because they usually end up in bricks.

Your best options are to use ODIN to restore to the version you had previously (the newer firmware), or use JTAG to flash the OS separately from the radio/bootloader firmware which causes the bootloop.

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[–] mrskeletaldootdoot [S] 0 points 0 points (+0|-0) ago 

AT&T neglected to release 5.0 so only 4.2.2 are on the interwebz. Unfortunatly I realized that the original way to root was to downgrade then use towelroot on a system that could be exploited. What is JTAG and how do you use it?

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[–] foxlet 0 points 1 points (+1|-0) ago 

JTAG is a connection bus that exists on the logic board of the phone, it is usually used at the factory to test hardware functionality and flash the final version of whatever software they plan to ship with the phone.

Most common setups use JTAG interfaces (such as the RIFFbox) and a set of cables to hook into your phone's logic board to restore firmware, but there is always more than one way to do it. I would recommend a quick search if you plan to use this method of flashing.

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[–] Bealski 0 points 1 points (+1|-0) ago 

Describe the boot loop, please.

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[–] mrskeletaldootdoot [S] 0 points 0 points (+0|-0) ago  (edited ago)

Well it's no longer doing it, now its just displaying encountered Firmware upgrade encountered an issue. Please select recovery mode in Kies try again with ODIN mode in the top left hand corner. to answer you question the 4.4.2 boot loop started up, had the Samsung logo, then that was it. frozen in time, nothing happened for at least 15 min before I pulled out the battery. the thing in the upper left hand corner says: product name S5 SM-G900A, Current Binary Official, system status official, reactivation lock: off Knox kernel lock 0x0, Knox warranty void 0x0. I'll try to get it to give you more information