It is happening while rig is on for several days. The fuse is old style one time use.
And have you tried changing the fuse to find out if it would work out. You may have an old type electrical (which is mostly the best) but change it and try another brand may be it could help. Also don't forget to protect it from power fluctuations... For example, where I am, electricity can go off and come back at anytime risking your electricals.