On reassembly, test the slider switch to make sure it works properly before putting the whole thing back together. If the external switch doesn't fit on top of the actual switch, it looks right but won't move.
I believe there are three washers on the case side of the logic board that can come loose at this point.
Don't accidentally remove the volume switch screws here. That comes later, and two of those screws are different from these and it's hard to tell them apart.