I think you need to give a little more information. What do you mean by they are not getting he needed 5V? Digital inputs 7-18 are a little different in the way they are set up but that should be transparent in most applications.
http://www.ifirobotics.com/docs/anal...al--i-o-rc.pdf
Do you mean you are not getting 5V at the 5v pin?
Or do you mean a 5V device doesn't operate when you hook it up?
Maybe you never read a "1" from the inputs?
If you are using a special circuit, you have a 1 AMP limit on current draw but I suspect obvious bad things would happen if you exceed that.
Anyway, no way to help without a little more information.
Steve