Has anyone blown a fuse on a Herpstat? If so, how easily is that replaced? I know I'll have to open the case, but beyond that is it pretty simple?

I'm pretty electronically inclined, so if I had it in my possession I'd be able to figure it out on my own I'm sure. I'm working on this for a friend, and want to know what I'm going to need before I get there (2 hour drive each way)...