SOURCE: LG microwave oven
It's usually a bad door switch or a broken door switch mount. Once in a while it's due to a board problem. If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info (as well as a text file which helps in diagnosing and repairing door switch problems) at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk
SOURCE: LG Convection Microwave Oven MC-7843D
A microwave can be dead for many reasons.
It may be the fuse, which is usually located on the floor of the oven behind the control panel or between the door switches.
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 thermostats, if it has a hood fan thermostat, that should read
open, as opposed to the others, which should read closed.
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 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.
We're happy to help and we appreciate your thoughtful rating of our answer.
SOURCE: I jus brought an LG microwave oven (MODEL
E-02 on the LED display.
That usually indicates a keyboard error...not a good thing...take it back and get a new one.
SOURCE: LG Microwave MH-685HD Owner's Manual
Try this website: http://www.service-manual-owner.com/lg.html You may have to email the person to get the manual?
SOURCE: How do I replace a LG LMV1630ST microwave oven door handle?
Normally
you have to separate the door panels (as shown in the attached photo)
and then you'll see the screws you need to remove.
Or you can watch a YouTube video (not a video I made) here that demonstrates how it's done.
We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer. 
Hi,
Here is a tip that will help you to figure out what is wrong with your Microwave Oven....
Basic
heatman101
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