I am trying to connect to Phantom 3 Professional. I have install DJI Go onto my Lenovo A7-50 7-inch Tablet MT8121. On switching on the controller and then the Phantom, when I go back to equipment on the tablet, there is no camera view. The camera moves when moving the controller sticks which seem to indicate that we are connected. However no camera view.
Any ideas ?

Have you tried "Enable USB Debugging" on your device?. Google it for your device. My issue was kinda like what you described and Enabling USB Debugging fixed the issue I was dealing with.