I took apart an old microwave oven just to see what happens with the circuit inside it. The overall idea is actually pretty simple, but I'm having a hard time figuring out some parts of the circuit. Here's a picture of the main circuit viewed from behind the LCD control panel:
At this point, I have figured out that the door switch must be closed for anything to work in the microwave, for safety purposes, obviously.
I have disconnected the magnetron and its transformer from the circuit. I found there are two wires leading to the high-voltage transformer for the magnetron. My main question is, when I'm probing the two wires, (white and red off to the left), I put the GND probe on the common ground (the metal piece to the right), and the positive probe to the wires. But each time I try this, both wires show 120V AC. Does this make sense? I'm thinking that one should be +120V and one should be ground. However, when I probe the two wires (positive probe on red wire, GND probe on white), I get 0V AC. How is the input to AC transformers defined? Both are hot or one hot and one GND? I feel like it should be a full circuit, with positive and ground to the input terminals of the transformer, and a higher positive and ground out from the output terminals.
(All this is done with the power plugged in and I've set the time on the LCD and have started it.)