How to enforce GPL to a HW manufacturer?

alexandre_ganso writes: "I have one of those media players, a small GNU/Linux box with a huge hard drive with tv and network output. In general it works great, but it has several small glitches, such as a buggy ftp server, internet radio support fails and goes back again from one version to another and so on. They have no interest in fixing most of these stuff, as newer products are priority. Eight months ago, I asked the for the source code, so I could fix it myself and return the fixed code to them, but they ignored me. Interesting to notice that the TVix HD M4000's user manual contains the full transcription of the Gnu General Public License, version 2! My question for slashdotters is: If they're using GPL stuff, and admit it, how can I enforce them to get me the source? It would benefit them, so I don't understand what dirty little secrets they may have...."