I have been looking for a way to reset my old AT&T Fusion U8652 phone to stock, because I had already rooted it and install a custom rom on it. Almost all research I have done did not have the answer I desired. Most answers found were to use a U8650 stock rom because those two phones are nearly the same. I didn't want to do that. I just wanted the original stock rom back on the phone. Then I found one piece of information, which led to a second, and now my Huawei U8652 is running its stock rom again! If you still own one, here's how to reset it back to the stock firmware.
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*** PLEASE DO NOT TRY THIS ON ANY OTHER PHONE. THESE INSTRUCTIONS ARE ONLY FOR THE AT&T FUSION U8652. I AM NOT RESPONSIBLE FOR ANYTHING THAT MAY HAPPEN TO YOUR PHONE. PLEASE PROCEED AT YOUR OWN RISK!***
Download the firmware for the AT&T Fusion U8652.
bit_ly/2fFF4vq (replace underscore with dot).
Extract it with your favorite archive extractor to your desktop or any other desired folder. It will include a dload folder, and inside will be update.app and update.xml.
Copy the dload folder to the root of your MicroSD card.
Power off your Fusion U8652. If you have not yet inserted the MicroSD card in the phone, now is a good time do so.
Hold the Volume Up and Volume Down buttons simultaneously, then hold the Power button. The phone will enter Software Upgrade mode.
Once in Software Upgrade Mode, the phone will automatically pick up the file from the MicroSD card, and it will install the firmware. It will first be Unpacking, and second Installing the software. After the update is complete, the phone will reboot itself.
The phone will reboot and the first screen you will see is the AT&T logo with the word at&t under it. The phone may reboot a few times with that same screen. Then it will show the next screen, the AT&T logo, but with the words Rethink Possible. (If it reboots more than 5 times without seeing Rethink Possible, you might want to restart the whole process.) Let the phone boot (may take a few minutes) and then voila! You're back to the original stock firmware!
Just to be on the safe side, you should do a factory reset on the phone. Go to Settings -> Privacy -> Factory data reset -> Reset -> Erase everything. It'll power off and do its thing.
Best of luck to you!