I finally received my radio keys and pulled the HU to get at the fuse in the rear. There was a 7.5 amp fuse that had blown so I was hopeful that was the reason for no power to the radio. I replaced it with a fresh 7.5 fuse, still no power. My question is, is 7.5 amps correct for the fuse on the rear of the HU? It's a 2000 A6 Avant with Symphony HU.