• ** 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

LG OTR microwave runs but does not heat

martyb46

Premium Member
Joined
Mar 4, 2015
Messages
3
Location
United States
Model Number
LMV1813SW
Brand
LG
Age
1-5 years
SORRY - I put the wrong Model # on this post--- Correct Model #LMV1813SW

I'm stumped... My 5 yr old microwave seems to run normally, but does not cook. I have checked the individual high voltage components (diode, capacitor, magnetron and transformer) -- all seem to be good, except the HV secondary reads 95 ohms, but I was advised that it should be more like 60-70 ohms; I've also verified that all interlocks are good, as the high voltage transformer primary is getting power when cook cycle is started, and after running for 3-4 seconds I can get a pretty healthy spark when I discharge the HV capacitor.

I am a retired electrical engineer, so I have a good working knowledge of the components involved, and the principles of operation of microwave ovens. Any other suggestions would be appreciated.

Thanks
 
Last edited:

martyb46

Premium Member
Joined
Mar 4, 2015
Messages
3
Location
United States
LG microwave runs but does not heat

I'm stumped... My 5 yr old microwave seems to run normally, but does not cook. I have checked the individual high voltage components (diode, capacitor, magnetron and transformer) -- all seem to be good, except the HV secondary reads 95 ohms, but I was advised that it should be more like 60-70 ohms; I've also verified that all interlocks are good, as the high voltage transformer primary is getting power when cook cycle is started, and after running for 3-4 seconds I can get a pretty healthy spark when I discharge the HV capacitor.

Any other suggestions would be appreciated.

Thanks
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,652
Location
Murray, Utah 84107, United States
I think you may need to test the HV components again. I divide the machine into two sections, low voltage and high voltage. If you have 120 VAC at the primary windings on the transformer the low voltage side is most likely OK and the problem is one of the HV components. Here's how to check them:
Microwave HV.jpg
 

martyb46

Premium Member
Joined
Mar 4, 2015
Messages
3
Location
United States
Thanks Rick,
I did recheck all the HV components... everything was in range except the forward drop across the diode was about 3.6v rather than the specified 1.8v. If that can be considered normal, then I'm guessing that the magnetron is being powered, but not generating mw energy. Does that sound like a reasonable conclusion?

P.S. I do notice some brittleness in the red wire at the transformer primary terminal, as well as some erosion of the terminal itself. What does that suggest to you?

Thanks
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,652
Location
Murray, Utah 84107, United States
Brittle wires is usually from a lot of use or heat from the current. I haven't seen brittle wires on the primary wires before. Could be from the tube. Just click on the part numbers in wildimagination's post for the links. Thanks wildimaginations!
 
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