No sound from radio

[quasi]

I'm in the market for a GX and found one at a local dealer. 07 with Navi and ML stereo. It's a little rough, but price is decent. Problem is the balance/fader is set to the right rear corner, cannot adjust and no sound from unit. Since it's not mine, I can't really diagnose it, and from what I've researched here on mud, it's not a system easily replaced with aftermarket.
Anyone expierienced this, or know a fix?
Is there a way to ditch the Navi system ?
Thanks