Bolero Screen not Diming with Lights

Last year I changed the Bolero radio in my 2012 Octavia FL (as per my sig) from a Delphi to a Blaupunkt unit as the Delphi had a tendency to occasionally change channels for a few seconds at random. Fitting the Blaupunkt unit has cured this problem but the Blaupunkt Bolero screen does not dim when the car lights are turned on. I seem to remember that the Delphi unit did dim with the lights on but I cannot be sure. I therefore have to have the screen brightness at medium which is just about readable in sunlight but not too bright at night.

The coding for both units is the same (090004000001). Before I get my VCDS cable out, and as it is very cold sat in the car, does anybody know whether there is a setting that I can alter with VCDS to make the Bolero screen dim when I turn the lights on? I have looked i the menus on the Bolero but have not found anything.

Thanks in anticipation

Richard