Help! Won't sleep when lid is closed

Hi everyone,

I just got a used air and it appears that the computer will not sleep when you close the lid. It has no issues sleeping if you click the Apple and then hit "Sleep".

I have torn it apart and put it back together and cannot find anything wrong other than it missing its left speaker.

I ran a magnet along the bottom edges and that did not induce sleep either.

Where is the sleep sensor this computer? Is it built into the board?

Thanks,

Scott