Berlingo Van 06 reg?

The radio/time display fades out completely after a few minutes and stays gone until the vehicle has been switched off for some time. The longer it has been switched off (e.g. overnight), the longer the display will last before fading (up to around 7/8 minutes). Also the clock needs resetting every time.
The dashboard display (speedo, mileometer, instruments etc) all work correctly and dont fade out.
Any ideas?