Had you replaced the transmitter or is it the original? Do the test again with the camera on and off to see if it rolls or is solid on the screen. Can you post a video of what it does with the camera on and when it's off.
The transmitter is a new one.
As you can see I have the camera off at the start and I already have the black screen. The transmitter dip switches are at default so I set the monitor to channel 1 band F.
I thought before it may have been the plug and play cable so if you remember I disconnected that and just connected a make do cable from the transmitter to the CAM port without the iOSD and I got the same result. Any ideas?