Thank you for the replies!
Here goes with some updates.
1. Try another SD card that you know works.
Card works OK
2. Try the current SD card in another device. These two options will rule out the SD card.
Card work OK
3. Set the camera to Bulb "B", take the lens off and activate the shutter. Do you see the sensor. Does the mirror lift? Do the shutter curtains open and close?
The mirror lifts and I can see the sensor. Not sure about the shutter curtains. What
4. Brightening the picture reveals nothing (i.e. it looks as if nothing has been written)
5. Exposing without memory in the camera the preview is as black as the final recording.
Are we approaching time to get a new body?
Regards and thanks
Roger Bowen