The fuse is what I think is called a spade type. It is plastic and flat with two flat prongs out the bottom and the rating on the top. Same as used in cars. I think it is located on the main circuit board. You should be able to see it by standing on your head and looking up at the circuit board.
It's a 2-amp fuse. When I was having problems with my Wallas, and had blown several in a row, I called the dealer, who told me to put in a bigger fuse. I've had a 5-amp in mine for several years.
Your fuse might be a different color, depending on it's amp rating. I'm using a 3 amp. Also, you might or might not have the spare fuse, one blade of which inserts into a female spade connector attached to a short wire.
If you going to replace the active fuse, I suggest you first pull the main power supply fuse located near the battery + terminal. That way, you won't short anything out on the unit's electronics panel.