Any suggestions what could be wrong here - something cheap and easy preferred

We seem to've mislaid the right channel on our Sony MDXC7900RDS (Sony naming scheme: (1) get all the letters of the alphabet; (2) shuffle them; (3) that's it).

I think the amp and speaker part of things is OK, since I can fiddle the balance over to the right of the car and it sounds loud enough. But when tracks have stuff happening in the right channel only, we can't hear it.

I know the MD is OK cos we can play it on other machines ...

Any ideas?

A.