What are the differences between the different revision of A600 motherboard?

I know the first one is branded as A300 on the motherboard and has one extra chip not present in later version (what does that extra chip do?). But what about later revisions?

My currently dead A600 is a 1.3, and looking online I can get a 1.5 replacement. What are the differences between those two? They look identical in pictures. And what changes were made for the version 2 motherboards?