Xantrex has discontinued service parts for all but their newest models, so you may have difficulty finding a place with parts for the older Heart Freedom 20. You can call Xantrex and ask if they still have parts available, but don't expect much joy. And Xantrex is not customer friendly either.
This document may help - see the part on the F2 fuse:
Here is one place that does parts and repairs. If the problem is a visible component failure, most any electronic tech can solder a replacement part onto the circuit board.
Xantrex Repair Parts
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL