I'm not sure about the radio because mine is long gone but I have had to replace almost all the bulbs that give the drivers seat its nightime appearance. I bought them over a period of time from a Volvo mechanic's shop. They were smaller than mini Christmas bulbs, came in green glass or regular incandescent and I had to take what I could get so the car is mix of them. I'd be willing to bet that if you take the radio out, you will see a wire going to a tube like spot with a little cap. Twist the cap gently and it may turn out to be the base for one of those bulbs. Or you will see a similar spot without the wire where the bulb base connects to a circuit board. If you're talking about the digital display, that cannot be serviced. Go to a dealership and request the part as if you know and see if they cough it up. On my other volvo, the V-70, three of the four are blown and the dealership tells me that they are not serviceable