GE Profile Spacesaver microwave would not heat and produced electrical odor. I replaced the capacitor and diode initially (easy to install) which eliminated the odor, but still would not heat. When magnetron was removed, I noticed a burnt spot on top which was an indication of a failure. After magnetron was replaced, microwave worked as expected.
Replacing the magnetron was somewhat cumbersome in the GE Spacesaver as it has a plastic housing in which the magnetron must fit into. This made it difficult to install and align the new unit. With some effort it eventually went into place. Overall it was not a difficult job.