• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake

FIXED LMV2073WW Microwave troubleshooting

Dave Pitman

Premium Member
Joined
Nov 22, 2014
Messages
8
Location
United States
Model
LMV2073WW
Brand
LG
Age
6-10 years
I could use a little help troubleshooting this micro.

For awhile, the unit was making unusual sounds, similar to an arcing sound but not quite. The oven heated satisfactorily though. Eventually the main fuse blew. I uninstalled it (it is a hood unit) and took the shell off. The 30 amp fuse was blown of course, and I found the HV Capacitor tested bad.

I replaced the capacitor and diode (even though the diode tested ok). I replaced the fuse and the oven seemed to work properly. I put it back together and re-installed it. It was quiet (only normal sound) for a few days but then the odd sound started again. This time, the oven is heating but not like normal, maybe 75 percent.

We have stopped using the oven but I have not taken in down yet. Do these symptoms point to what might be the problem. Unless it is just a coincidence, probably whatever is at the root of the problem led to the capacitor going and then the fuse thereafter. The transformer looked visually fine, although I didn't do any testing on it. I'm not sure what to do next.

Thank you for any help getting to the bottom of this.

Dave
 

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Dave Pitman

Premium Member
Joined
Nov 22, 2014
Messages
8
Location
United States
Thanks Rick.

Mag antenna looks ok (I think). It has a very slight discoloration but I'm assuming it gets hot and the slight color is normal?
It tests good, .2 ohm between terminals and no continuity between either terminal and case.

The transformer tests as follows:

Across primary High - Low: .2 ohm
Primary High to case: inf.
Primary Low to case: inf.
Filament Lead to case: inf.
Secondary Lead to case: 69 ohm

Your thoughts?
 

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rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
33,174
Location
Murray, Utah 84107, United States
It's dark enough I would say the tube is the problem. The transformer is good and you replaced the HV cap and Diode. Assuming they were new and good that just leaves the tube. Can you tell where the noise is coming from?
 

Dave Pitman

Premium Member
Joined
Nov 22, 2014
Messages
8
Location
United States
Haha, I thought you might ask that! There is no safety concern turning the unit on with the oven shell off so long as the Mag is installed where it belongs, correct?
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
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Messages
33,174
Location
Murray, Utah 84107, United States
You're correct. You're not taking any voltage readings so just keep your fingers off the wire ends and no problem. Don't run it empty put a cup of water in the oven.
 

Dave Pitman

Premium Member
Joined
Nov 22, 2014
Messages
8
Location
United States
It's very difficult to say definitively where the noise is coming from exactly. Using a glass as a stethoscope, the transformer is definitely making some noise but I can't say for certain it's the intermittent arc-like noise or just a general hum. I can't detect any noise when placing the glass on the mag cover.

I have on hand another HV Cap and rectifier (diode) and swapped those in and it made no difference.

I did the 1 liter water for 2 minutes test and the oven only raises the water temp 20 degrees.

I don't mind spending $60ish for a mag or the $100ish for the transformer. But not knowing which for sure, or even if it might be something else entirely makes me hesitant of ordering either part.

I much prefer fixing if possible. But in this case it may not make much financial sense. I'm open to any additional advice.

Thanks a lot for your help, Rick!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
33,174
Location
Murray, Utah 84107, United States
You have already diagnosed the problem my friend. It's easy to overthink and start second guessing when it comes to microwaves. You already know you're getting the correct voltage to the high side (primary windings). You already know the HV cap and diode are good because you swapped them out and you already know the mag tube is getting voltage because it raises the water temperature 20°. The measurements you took on the HV transformer were good so the transformer is good. If you put that all in a pot and stir it up, you'll come up with a weak tube. Replace the tube and you're good to go.
 
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