I Have 2 controllers and have yet to have the second one (camera control) work with any display.  I can control the camera but the display does not work.  Ipad, Galaxy Tab S,  Galaxy note 4.  I did try to update firmware in it and it didnt take as well.  Called DJI and the gave me the run around.  I would love it to just work but i believe the USB port is bad as it doesn't take firmeware or see the Tablet.  Any ideas.  

tried using it as the primary controller instead? does it work then? try the hdmi port instead of usb?

Sounds like it's not on the same firmware version.   I had this exact problem, the second controller would move the camera but said NO SIGNAL and wouldn't display the image.

For me updating the second remote corrected the problem but it sounds like the inability to update is the issue.  

You haven't said anything about what happens when you attempt to update.   Does it beep?  Does it go into update mode?

IMPORTANT QUESTION -  did you successfully update the primary remote?   If so did you remember to remove the TXT file from the SD showing the SUCCESS of the update before updating the second remote?   If not this is probably the issue.

On a slightly different but related topic: where can I find the firmware version for the controller?  So far, I know about hitting the center bar in the Pilot App and it will tell me if everything is up to date but I've not found where I can go to get the level of each piece so I can verify it somewhere like the DJI website.

I followed the update the instructions and repeated it for all my batteries and controllers and checked the .txt file each time and they were all happy.  I've not had any issues but I trust nothing (I do computer support so I know better).  It would be nice if I could see the version loaded somewhere.  This is particularly true of the second controller because it is not going to link up with the craft and so the usual display for the firmware doesn't come up.

I suppose all of the above could be rephrased: How do you check the firmware level of the 2nd controller?

My second controlled never worked.  IT does nothing at all when I try to Upgrade it No sound now blue light.  I've call, Emailed and texted DJI on this and I have gotten nowhere.  No my primary is doing the same thing.  I've tried ne USB(S) cables and the new 3.0 App  nothing