Having been forced years ago to repair non-existent microwaves down here I can tell you some of the troubleshooting can be done with a digital multimeter and beyond that it's guess and by golly...
The high voltage section is beyond my ability. A long-gone friend was the head radar tekkie at Vandenberg AFB and even he was reluctant to delve into the high voltage finals without incredibly expensive test equipment...
"Whaddya gonna do when you find something in the HV section gone bad?"
"Lookit. These people who build these things are so cheap they don't bother to put in a memory retention lithium battery in, for the clock"
In Mexico darned near every appliance has a repair warranty outlet in any one of 80 cities. From experience I can tell you they will repair switches, touch button panels, and electronic control circuit boards. When high voltage is concerned, no parts and no interest to delve into the machine.
Know when to hold em -- know when to fold 'em...