Be very careful with this. Very high voltage from transformer and Capacitor. And you can cook yourself if you are not careful. Don’t test with door open. You really don’t want a microwave burn. That said, test the Capacitor. if it is bad they are not very expensive. Careful there also. It stores a very high charge. Next is the Transformer. I’ve seen them burned out. Check for open windings. Cooking dry stuff with out water in the unit will burn out the magnatron. An example of this is heating corn tortilla chips. They are so dry that much of the RF can return back to the magnatron back up the wave guide and kill it. To prevent this put a small cup of water in the corner of the oven to absorb the extra RF. This probably is not your problem but I will add that a very common failure point is the fuse caused by just opening the door too fast. If the door safety switches don’t close fast enough the fuse will blow as a safety fail-safe. Again this is a very cheap repair. And a common failure that puts many microwave to the curb ready for an enterprising fixer to grab them up replace the fuse and have a good appliance. I don’t do much at the board level but as others have stated your controls may be working but there could be other hardware issues as I’ve described. Good luck and be save. One last thing, High Voltage gloves aren’t a bad idea when testing microwave components.