My Laptop (Dell Vostro 3300) internal speaker (yes, it's mono) is mute already for some time, and I was just patient with this problem, because the sound quality is ridiculous anyway and I always used either headphones or external speakers. But I wanted to fix this nevertheless, for those few times I need that pity internal speaker.
There was no problem initially, but it appeared something like couple of months ago. It might be related to OS upgrades (Ubuntu 12.04 LTE right now), but, on the other hand, if I boot Live Mint 12, then there's no sound on speakers there neither. I thought that the problem might be hardware related (ie, the speaker is just plain dead), but I'm not sure how I could check that. Another explanation could be that the system thinks that the earphones jack is plugged in and the system just doesn't switch to the speaker output.
I surely hope this is some strange driver problem though and, thus, fixable. Would be happy for any ideas how to detect that.
Edit: I have increasing suspicion that the failed sense pin in headphone jack is to blame, so this is not Unix/Linux topic at all. Alas, there are no tests on this model to detect that.