AFAIK the A520 does not work with "big box" Amigas due to them having an unbuffered video output on the 23 pin video connector.
A2000, A3000 and A4000 all have video slots which is maybe the root cause of them having unbuffered outputs? Not sure.
I used an A520 with an A2000, and it locked up all mouse movement! As soon as the A520 was removed, mouse control came back.
Truly,
Robert Bernardo
Fresno Commodore User Group -
http://www.dickestel.com/fcug.htmSouthern California Commodore & Amiga Network -
http://www.portcommodore.com/sccan