Did you try cleaning the inputs? If so, take a pin, bend the very tip and insert it into the input. Try to catch ont of the metal strips on the inside of the input and when you do, try to bend it down a little bit. Don't force it as you don't need to pull it out that much. That should fix it.
I had to do that on my PG QX2180 a couple times now because loose stuff in the trunk would occasionally hit it.
If that doesn't fix it, look around the RCA input assemble on the main board. Look for very small hairline cracks. I just bought an Alpine F407 that had a cracked board. if it is cracked you will have to break out the soldering iron and patch the board. drill two holes (used the smallest metal bit you know exists) in each path on the borad that is being interupted by a crack. you'll need to put in some wire from one to the other and solder it in place. then cover the whole mess with some liquid electrical tape and you're set.
