I bought a used Harmon Kardon AVR-7000 amp. I am hooking up my dvd player. When I plug in the RCA input to the dvd input behind the amp, and switch to "DVD" source, there is no sound. But when I switched the RCA cable to the "CD" input, and select the CD as the source it works. Can it possible be a bad DVD input connectors? If so, how much do you think it cost to get it fixed? Is there an easy way to fix it myself? Thanks in advance.