I was hoping to find one of your vintage but there weren't any there - I wanted to try some diode tests so that I could tell you which ones and how to test them on yours. At this point I'm still hesitant to advise purchasing a new control board UNLESS you can find a dealer whom will let you return it if it's not the problem. Meanwhile you might want to start checking around for a used one.
Many things are powered thru the slow blow fuse...
Charge Resistor (back of gen, you cannot see it)
One more thing we can try taking a look at is the brushes, and of course the slip rings. Are you familiar with where your brush block assembly is located on this unit? They're mounted in a small plastic block behind a large black plastic cover which simply snaps into place at the END of the bell of the generator stator, facing you. Two wires run to them, clearly marked F1 and F2 on them,(mark their location on the brush block so you can put them back on exact), 10mm socket for the 2 bolts holding the brush block in place.
They are extremely easy to remove, check and service on your model. It is possible that the brushes are worn to the point where the brush assembly has burnt and could possibly be shorting the brushes. I can see where this would cause the control fuse to blow. The control board applies a field flash voltage thru the brushes to begin the initial excitation as the unit gains speed/rpm- if there is a short there then it could easily cause your problem. Once you remove the brush block and the wires are removed from it(tape them up so they don't touch anything), try starting the generator again. Your model will run without the brush block in place. If it still blows the slow blow then we can start looking at other items in the list above...
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified