Thanks for all the useful suggestions and information. I started off by inserting 'sudo adduser $USER dialout' and received notice that I was added to the dial out group. Then when trying to add the firmware in the usual manner, same result: permission denied. I have given up on Linux and switched to my iMac. That worked first time. I now have the latest firmware installed.
Then I removed the jumper and started up again, using 7.5V. Black boxes.
So I read and printed the post Hans put up and which Roger pointed me to. I inspected all the solder joints to the LCD header connectors, found them to be okay but still reflowed the solder on each just to be sure. Same result - black boxes.?
I then checked the voltage at each pin of the 2x5 LCD header as mentioned by Hans. I fired the rig up and probed each pin with a DMM. All showed 0V except pin 3 (inside rail from the top) which showed 4.47V.
So I guess I have made some progress.
Grant
Grant