Back up from Imac to Time Capsule

I have beeb backing up my Imac to a 500G Time Capsule using time machine in a wifi environment. It has been working fine, however, recently it has started to do full back ups (about 160G). I'm not sure why this is, I read somewhere that it could be a corrupt file and to check in console in Utilities. Needless to say console seems to have dissappeared. Any solutions and can I repair the Ulitiities using my Leopard disc if necessary.