If a fuse has blown it could be that the macerator is stuck or jammed.
If your macerator is like my RV Sani Con there is a slot at the end of the unit. Use a flat screw driver blade to gently turn the shaft counter-clockwise. This may "un-stick" it.
Things like tissue or human hair can cause jamming. Sometimes, in-activity can cause the shaft to seize up too. I always use a screw driver to turn the shaft a few times before using the macerator in such a case.
Here's an owner's manual should your unit be similar. See page 9, TROUBLE SHOOTING for illustration.