Some faces turned to black

I’m new to Blender, therefore sorry for my noob question, if it is.
Searched about this problem, but not found solutions, perhaps I was lazy… :slight_smile:
So, here is the problem>
I’m making a mesh using extrude, scale etc., but after something some faces on the mesh turned to black.

Yeah, I know, I have recalculated the normals, didn’t help… :eek:

What’s wrong? What should I do?

Thanks for helping!

remove doubles perhaps.

Baah, the mesh was duplicated…:spin: