radio button lights not working

[jbone]

I just bought a used cd player for my 02' Sierra off of ebay. The seller didnt mention any problems with it at all. I just sent him a message but he prob. wont answer for a while. The problem is that only some of the buttons that are supposed to be lit are lighting up when I turn the truck on. Everything else works fine, just not the lights. Any ideas on what could be wrong and how to fix it??? Thanks!