A microwave can be dead for many reasons.
It
may be the fuse, which is usually located behind the grille or on the
floor of the oven behind the control panel or between the door switches.
At
our site, we have a video showing how to remove a typical
over the range control panel assembly in under 5 minutes.
If
the fuse is good, it may be an open thermostat or thermal cutout (TCO)
/ thermal fuse on or near the magnetron or on top of the cavity / body
of the oven.
If it goes dead for a while during or after cooking
then comes back on, the magnetron is probably overheating and causing
the magnetron thermostat to open.
Then when it cools, it closes the circuit and allows power through again.
When
checking TCOs or thermostats, if it has a hood fan thermostat, that should read
open, as opposed to the others, which should read closed.
The
TCOs you need to be concerned usually with have all black or white
wires only. Please reply with photos of your interior if you have questions.
If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.
If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.
If
it goes dead or blows the breaker (or GFI) when you plug it in or open or close
the door, then there's a problem with a door switch or door switch
mount.
If it's intermittent or random, it may be a bad
connection, usually on the control board or a loose fuse holder, or
even an intermittent fuse.
You should do a continuity test on
the fuse while it's in the holder (with the microwave unplugged, of
course) then turn the fuse by hand or take it out and put it back in,
then test it again.
If you remove the fuse, then press the meter
leads against the ends, it can allow internal contact to be made and
make a bad fuse appear to be good.
If you or someone you know
decide to look into it, we have critical safety information and
disassembly information at our site, and our link is at our listing
here on FixYa.
In some brands, there
is a "mini-manual" hidden inside the unit behind the
control panel or hidden on the left side behind the grille, which is
very helpful when troubleshooting & testing.
If you'd want to scan and e-mail or copy and fax the mini-manual (or at
least the "schematic diagram page) to me, I'd be happy to make more
precise suggestions.
You can usually find helpful exploded view diagrams and order parts by entering your full model number
here.
We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.