Diagnosing display problems

So I bought a MBA 1304 from a buddy. He said his LCD went bad and he didn't have the time to deal with it, so I got it for really cheap. However, he said he didn't crack it or anything, it's just black. It works fine if hooked up to an external monitor, I guess I'm just trying to figure out if it's the LCD or the "inverter" or whatever they're called on the MBAs. Any ideas?

Thanks!

 

Just held it under a really bright lamp and didn't see anything. Is this an indication that it's the LCD? I see they're not that expensive, I can still come out ahead if that's all it is. I would just hate to buy one and it be something else.