Internal Microphone not working - Early 2011

Hi all. I wonder if someone has a good tip for my problem.

The internal microphone on my Early 2011 15" MBP isn't functioning. It has worked previously, and I can't be sure when it stopped working as I don't use it very often - but it is annoying. No matter how loud sounds I produce, it registers no input.

I've tried resetting NVRAM and SMC without positive results, and as far as I can work out, all my audio settings are correct (see screenshots).
The thing is, I had my machine in for repair about six months ago for the infamous video issues, and I have a small feeling it stopped working after that (based solely on the fact that I can't remember it not working before the repair, and I can't remember it working after). Is there any way I can check via software if the hardware related to the microphone is connected properly inside my machine, or check it easily manually without taking the logic board out (which I'd rather not do)?

Or any other thoughts?
Thanks!

(Running 10.11.1 by the way.)

 

- Thanks. If the mic were not connected at all internally, you would expect it to not be listed under audio devices in system preferences, correct? The fact that it is listed suggests it is connected internally. And if that's the case, I suppose I have nothing to gain by opening it up unless I plan to replace the mic with a new one.