Originally Posted by Simon_Gardner
I'm obviously not explaining this properly. Almost everything else: drives, phones, cameras, SD cards in card readers, CF cards in readers, satnavs, thumb drives, other computers, CDs, DVDs mount on the Mac desktop as effectively an external drive which is a lot more convenient for various reasons. This phone doesn't. Even the MicroSD card taken out and put in a card reader doesn't.
Can't fix the issue you are having, but Airdroid is a great work around. Allow easy access to all your phone files..external sd, internal and everything else without having to plug anything in, you can easily copy files from your mac/pc to your phone and back. https://play.google.com/store/search?q=airdroid
My s3 would not be recognized as an external drive with the cable provided I used an old nokia cable and it worked, but found I liked the wireless option better. As for the sd card my only guess would be in the formatting. Hope you get it going the way you want, nothing is more frustrating that trying to do something the way you are used to and it not working.