As in your case the fuse keeps on blowing, thereare couple fo things that you will have to do fix it:
The problem your describing is most likely a cap problem. The transformers operate in saturation and therefore it's not likely to blow out the diode. The transformer is essentially energy limiting.
The capacitor or diode may be bad. Discharge the capacitor as described earlier in the article. Test the capacitor by removing the leads and setting the VOM to RX100. Probe the terminals. The reading should start in the low ohms and increase toward infinity. Reverse the probes and re-test. The reading should do the same thing. If not, it's bad. To test the diode, disconnect the diode from both the appliance and the capacitor. With the VOM set to RX100, probe the wires. Then reverse the probes and read again. You should get infinity for one reading and low ohms for the other reading. If not, replace. Another cause could be a faulty magnetron, but due to the sensitivity of that piece, it's best left to a professional.
You can see the diagram of you model in order to do further repairs by going to the below mentioned link:
Choose you model no. and on the next page on the extreme left you will see the diagram of you model, click on the diagram to see a enlarged image.