I picked up 2 Phantom 4 drones relatively cheap, I knew they had problems. The Phantom 4 pro fly's good, but there is no video transmission at all. The led on the SD card flashes 3 red, I know the SD card in the slot is a good one. The second drone which is a Phantom 4 has good video transmission but wont fly. It will not calibrate the IMU, get an error code -50. Tried to calibrate many times. I am hoping I can take parts off of one to get at least one of the drones working. Where would you start? I also have a phantom 3 that I have had for several years that works perfect.