I had real issues updating the remote firmware last night, initially using the three standard update procedures: Microsd with adaptor, USB stick and direct connection to phantom 3 camera.
Nothing would initiate the blue led until I did a cold reboot of everything: phantom 3, remote and iPad.
Once I then restarted the DJI Go app, checked status and was then able to update via the app. Just make sure you have the latest version, and plenty of charge in your remote and iOS/android device.
Hope this helps.
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