Hi,
I located some pictures of A570 and it looks exactly the same as my A690.
I can send you a pic of the main PCB and talk about the differences if you want. :-)
Also some A690's did look different (The early ones).
Where did you get the A690 from?
An owner of another A690 was on comp.sys.amiga-hardware a couple of months ago, you may be able to see his posts if you look.