I've got a phantom 3 professional I bought with liquid damage to the camera. I've fitted a new 4k camera and gimbal off eBay but it still don't work. It will fly ok, take pictures and videos viewable from the SD card. I've tried with my phone (Huawei P30 pro) and shows no error just a grey screen, tried with an iPad air it shows two different messages. Sometimes it says weak image transmission and the screen is black, the other is no image transmission signal and the screen is grey. I repair computers so have a good understanding of these things but I'm unable to figure this one out. Things I've tried is. Downgrade firmware, relink RC, new ribbon cable (even though it was saving images and videos to the card, different devices and leads, recalibrate, checked for loose wires. Hope someone can help.