Zoom (Universal Access) with strange behavior.

Some time ago, I upgraded my father's eMac to a 2011 iMac.

I upgraded the system as recomended, connecting the old eMac as an external drive and follow the Migration Assistant Wizard to get the old user to the new iMac as a second user.

When I use Zoom (Universal Access) on the eMac, the fonts got a rare rendering. I suppose it was because the lack of power and memory of the graphics card.

However, in the iMac (and just with this upgraded user) the problem is the same. If I zoomed another user, there is no problem and the fonts appears as normal zoom (as in my MacBook Pro).

I suppose it is a library problem, but I don't know where to start.

Any suggestions?