Tried that - still no response.
Checking the pcb tomorrow with a multimeter.
I'm not sure if it's something to do with wiring all the cables from the flight control board into the receiver: given that everything spins up and works on the initial calibration I would have thought it was unlikely to be a short on the pcb.
I've attached a couple of pictures of the bits around the receiver and a couple of photos from libre pilot. As you see, there's an acknowledgement from it that there is input into the channels, but it isn't actually showing what the sticks are doing.