Audio Systems: Car radio malfunction in a Mercedes, worst case senario, fuse box

Question
Hello, I am writing to try to find out information on My Girlfriends car. Its a Mercedes Benz SLK230. 2 mornings ago she went to start her car and her radio was dead, did not initialize, no lights nothing, it was just dead. It is one of the factory OEM units that I have heard is a real pain to try and work with. I took the unit out to check the fuse in the back of the head unit, as that was my first thought, Then I checked her fuse box under the hood, and all of those were intact. I took my voltmeter to check the power supply and it had both the constant and the switched power. So does that mean that her head unit is shot, or is there an easier fix that I am not thinking of. where is the amplifier located in that car, one of her friends said there may be a fuse on that that had blown, but I dont see why that would effect the functionality of the head unit itself. Her warranty has run out and I am trying everything that I can do without having to have her take it to the dealership and be overcharged. secondly, and this is a worst case senario and the head unit its bad. Is there a way to get a non OEM head unit to integrate with the existing hardware, she would really like one with MP3 function.  

Answer
Brian,
I have found on a few of these stereos that the trimmer capacitor for the clock frequency adjustment will sometimes short out and this will make the stereo non functional. The best way to see if this is the cause of no function, is to pull the stereo and connect it to an external power supply to check it out on a test bench. Please give me the complete model of the stereo and the year of the vehicle.

TOM,
T&D ELECTRONICS,
tdeser@zoominternet.net