• ** 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

Panasonic Microwave will not run when kitchen is chilly

chaslp

Premium Member
Joined
Sep 16, 2013
Messages
3
Location
Oak Lawn, IL
Model
NN-P294WF
Brand
Age
6-10 years
My microwave will not run when the kitchen is chilly (say, 70° or less). The unit will run for about 3 seconds, then shut off. (Panasonic NN-P294WF)

If the hood light is left on for, say, a half hour to warm up the unit, everything works perfectly.

I know these units won't run if too hot, but not running when cold is puzzling. Any clue as to which component may be suspect would be appreciated.

Thank you.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
33,117
Location
Murray, Utah 84107, United States
I've not heard that before for any appliance. It must be something on the electronic control board. When it stops after 3 seconds will it turn on again for another three seconds? Because it's a Panasonic, service information is sometimes hard to find. Do you have your tech sheet and can you post it here? I'll see what I can find. That model uses a noise filter. Check that for any loose connections and check the thermostats/TCO's for loose connections.
 

chaslp

Premium Member
Joined
Sep 16, 2013
Messages
3
Location
Oak Lawn, IL
Thank you for replying, Rick.

Yes, when the microwave is cold due to the ambient temp of the kitchen, the unit stops running after 3 seconds. It will immediately run again for another 3 seconds, and so on. However, if the kitchen is warm, or the unit has been warmed sufficiently by the hood light, it will run for the complete cycle requested, and it will never stop mid-cycle. Weird, eh?

All connections seem tight. This (cool) temperature issue is obviously now rearing its head due to cooler fall mornings.

Unfortunately, I did not receive a tech sheet, only the operating guide.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
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Messages
33,117
Location
Murray, Utah 84107, United States
Panasonic MW Service information

OK my friend, sometimes you get the bear and sometimes the bear gets you. This time we got the bear! You'll need to use both the tech sheet for your model in concert with the Panasonic service manual for testing procedures. You have your work cut out for you trying to figure out what's causing the problem. Concentrate on components that have to do with temperature like the TCO's and thermistor. Then try to run the service tests for the model that most resembles your model by comparing the control boards in the service manual. Good luck and if you have questions just post them here:
 

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chaslp

Premium Member
Joined
Sep 16, 2013
Messages
3
Location
Oak Lawn, IL
Hey, Rick. Thanks so much for the tech docs.

Even though my problematic microwave was working like a champ all day today, it is still a sick puppy. I've got some new symptoms to report which are probably indicative of the underlying problem.

When the microwave starts up, I hear a very soft buzzing for a few seconds. Simultaneous with this buzzing, GFCI receptacles trip in both of my bathrooms. Huh? And these GFCI's aren't even on the same circuit as the microwave!!!! To me, these symptoms of electrical interference are pointing to trouble-a-brewing in the power supply circuitry.

About 3-4 years ago, I replaced the inverter because the large power transistors (or were they diodes?) had fried. I'm kinda remembering the same buzzing at startup just before that incident. I wonder if this is deja vu all over again.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
33,117
Location
Murray, Utah 84107, United States
chaslp said:
Simultaneous with this buzzing, GFCI receptacles trip in both of my bathrooms. Huh?...symptoms of electrical interference
I'm suppose to say Huh?....lol. Start with the noise filter. I don't know what else it could be if they're not on the same circuit.

chaslp said:
I replaced the inverter because the large power transistors (or were they diodes?) had fried.
You're probably referring of the rectifier. It's actually four diodes connected together to change AC to DC and it does make a low pitched hum when it goes out. The microwave inverter isn't as common as the separate high side components are. It's fairly new technology or at least to me it is. Ninety nine percent of the microwaves that I've worked on don't have an inverter. My knowledge on inverters is limited. I think there's a test for the inverter in the manual. READ THE WARNING before doing any tests on the inverter. I haven't had to test any inverters yet so I don't know if that could cause the temperature problem. Start with the noise filter then the inverter is how I would proceed. The tech sheet and manual will probably be more help than me. Sorry I'm not able to be more helpful my friend. Keep us posted on what you find out. Did you hear a bear??......
 
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