I put you in the right Category and Edited your question.
Only authorised service engineers have schematics to microwave ovens. The reason is that they are extremely dangerous to work on, super high voltage held in the capacitor, the poisonous core of the magnetron and the ability of microwaves to make you blind in 5 seconds. The case is fastened with safety screws for a reason.
Contact the company and ask them for the schematic. Tell them you want to open it up and fix it.