Volume stuck at highest volume, slider isn't working.

My volume slider of my new 3DS (not XL) isn't working. I can slide it around but it doesn't change the volume. I opened up the top part of the 3DS and the volume slider seemed to be in sync with whatever it needs to slide around. It's wasn't derailed or something. It just doesn't change the sound anymore. Has anyone had this problem before or know how to fix it? My warranty is over so I have to do it myself.

Greetings

Emile