Interesting schematic. Even though it's a 240 volt microwave, all of the components are 120 volt. If your cooling fan and turntable work, you know you have power to that point. Check for 120 vac from the blue wire at the fan relay to the red wires on relay2 on the control board. If you have power there, you should have power to the HV transformer unless there is a break in the wire. If no power, check for 120 vac from the fan relay to the primary interlock switch. It's the door switch with red wire and a brown wire with a yellow stripe. If you have power to the HV transformer, the problem has to be on the high voltage side. Check your high voltage components. Unplug the microwave and discharge the HV capacitor. Check the primary winding and both secondary windings of the HV transformer for continuity. You can check the HV diode with a 9 volt battery, you should read voltage in one direction and 0 in the other. Check the HV capacitor with a capacitor checker. If you don't have a cap checker use the resistance setting of your meter, you should see a jump in resistance that then immediately rises to infinite. If not, reverse the leads and try again. The magnetron should have less than one ohm resistance between the two terminals and infinite to ground. If everything checks good, replace the magnetron.