If I had to guess I would start with the 3 in 1. I have pluged in the power to the rx backwards before and it was ok. I dont think there is any protection on the 3 in 1 for plugging it in backwards because you shouldnt be able to do that with the stock plugs. If you know any one that fly's airplanes see if you can use a switch and a recriver battery pack and just test the receiver, but make sure that the 3 in 1 is disconnected from the receiver.