Well this appears to be the same problem that I sent my quad back to Banggood a few months ago. I'm better at taking it apart now and honestly, this one was my fault... I was out flying a distance away and triggered a RTH (return to home) because of weak signal strength but after the quad returned to LOS from me, I overrode the RTH and began to fly around locally. Well, it's well known (at least to me) that if you override RTH, then that's your last free ticket with the Upair, the next failure, such as a low battery RTH will fail and the quad will fall out of the sky!!! (and that's what happened!)
After picking up my camera and the broken landing gear, (my UpAir fell from about 60' on soft sand!) I tried starting the motors again but it wouldn't arm any longer. I took apart the drone to look for any loose or broken components but there wasn't anything visibly wrong so I just kinda left it on the bench for a couple of months while I tried to research the issue. I've had luck with heating some electronic components to I got out my heat gun and heated up the SD card where it had been super glued by Banggood. I gave it good heat cycle, probably 300-400° for about 60 seconds and after letting it cool again I mounted the battery on the board and tried powering it up. After a normal startup sequence, I tried to arm the motors again and VIOLA, IT WORKED!.
Well that would explain Banggood super-gluing the SD card in. A loose connection on the card would cause the quad not to be able to complete it's boot sequence and not let the motors arm.
Update: I'm not positive that the SD card was the problem, I also heated up the IC located on the center of the daughter board. It also could be that component but it's enough of an issue to take the UpAir apart that I wanted to heat both components just in case.
The bottom line is that my UpAir is STILL flying and although I haven't electronically logged each flight as I have with my Phantom 3 Pro, I've flown the UpAir just as much or even more. Right now, I have 30 hours and 201 flights on my Phantom 3 Pro, and I have at least that much on the UpAir too!
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