[Panelman]

I have had a loud buzzing sound coming from the microwave for quite a while now, but everything worked fine, until recently now it no longer heats, everything else still works. Any ideas?

[applianceman]

Typically the buzzing sound will be caused by a bad diode but if you have a bad diode it will not heat.

What can happen is the magnetron tube can arc causing a noise but sill heat then eventually stop heating.
If the diode is bad you need to change the magnetron tube and the diode.
The noise and the heating problem may be separate issues.

I think your magnetron tube needs replacing.

These two pages should help

GE Spacemaker Microwave Magnetron Tube Replacement

Microwave Repair Guide

[Panelman]

Thanks for the info, how do I know which diode I would need to replace?

[applianceman]

Most cheap ohmmeters will not check diodes. But if you have a good one Disconnect the diode from the capacitor, set you meter to highest ohms setting. Check ohms across the diode, it should read open one way and very high ohms the other (50K-100K). If it checks shorted both ways it is bad, if it checks open both ways it is bad, but if your ohmmeter will not read that high it will check open both ways anyways.

Typically if it is noisy it will be shorted both ways and any ohmmeter will check that.

The capacitor will cause a buzzing noise as will but it will also cause the microwave not to heat.

To check the capacitor disconnect the wires and place your ohmmeter across the capacitor. The ohmmeter will read ohms at first that go to open, and then reverse the leads and it will do the same again.
This is not nearly as common as the diode and magnetron tube but can casue your problem.
Be sure to disconnect the power before attempting to check any of these things.