No Sound On N64

Hi there, I'm new here and I'm having a bit of a problem with a free N64 my friend gave me. I can get a picture but no sound. I have tried different leads, different televisions, different games and opening it up and cleaning it out with alcohol and cotton buds but I just cant get it to produce any sound, not even static. I have some experience with soldering and modding if that helps.

Any suggestions would be greatly appreciated.