• ** 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

Microwave fuse keeps blowing

keno1

Premium Member
Joined
May 5, 2012
Messages
6
Location
Australia
Model Number
nn-8550
Brand
-major brand-
Age
More than 10 years
Have a Panasomnic NN-8550 microwave that, to quote the boss "made a funny noise and stopped working". When I looked at it, there was no power; even the display was dead.

Pulled the cover off, the fuse was blown, so replaced it. When I plugged it back in the display powered up as per normal and I could set the power level and time as usual. When I pressed start it sounded like normal and seemed ok, but after about 1 sec there were 3 or 4 clunking sounds then it stopped working and went dead. The fuse had blown again.

I have checked the thermal cutout with my basic multimeter (seems fine) and I took the capacitor with me to the electrical store when I got some more fuses and they tested it for me and said it was within tolerance.

From what I have read, it doesn't sound like it is the Magnetron and I haven't tested the diode as I am not sure how to.

I am a novice with microwaves so hope there may be some knowledgeable people out there that may be able to suggest what I should do next to identify the cause.

thanks
 

jeff1

Appliance Tech - Moderator
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Hi,

Quote:
When I pressed start it sounded like normal and seemed ok, but after about 1 sec there were 3 or 4 clunking sounds then it stopped working and went dead. The fuse had blown again.

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More often than not, a shorted high voltage capacitor.

Quote:
I took the capacitor with me to Jaycar when I got some more fuses. They tested it for me and said it was within tolerance.

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Check it again.

http://www.applianceaid.com/micro4.html

Quote:
From what I have read, it doesn't sond like it is the Magnetron and I haven't tested the diode as I am not sure how to.

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Usually the mag or diode won't blow the fuse, they may growl or make a strange noise and stop heating but normally don't blow the fuse.

Testing...
http://www.applianceaid.com/component.html

If needed:


Capacitor, hv Manufacturer Number A60905500AP

jeff.
 

keno1

Premium Member
Joined
May 5, 2012
Messages
6
Location
Australia
Capacitor

Quote:
Check it again.

http://www.applianceaid.com/micro4.html

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Thanks Jeff,

I have pulled the capacitor out of the microwave again and have tried to test with my digital m/meter. Have followed the instuction on your link, however have a couple of questions.

1st up, the instructions suggest setting on Rx1. My m/meter has 20M, 200k, 20k, 2000, 200 settings. Internet research says that Rx1 is equivalent to 200. Is that correct?

2nd, the testing instructions say to "touch the cap terminals ( red lead on left and black lead on right )" Excuse my ignornace, but that is a bit confusing for me. 'doh! As I look at the capacitor as it would be positioned in place in the microwave, there are 2 caps. The left side has 3 terminals and the right hand side has 1. When I connect the red m/meter lead to any 1 of the 3 terminals on the left cap and the black lead to the terminal on the right cap, the reading stays on 1 and doesn't change at all. When I reverse the red and black leads, the reading again stays on 1.

I am not sure if I am testing the capacitor correctly or whether the capacitor needs to be replaced. BTW, the capacitor is not out of shape or bloated and there are no signs of any oil.


Hoping someone can help with the next steps. Thanks.
 

jeff1

Appliance Tech - Moderator
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I have pulled the capacitor out of the microwave again and have tried to test with my digital m/meter
Needle meter is used...especially for microwave stuff...that's all we use.

the capacitor is not out of shape or bloated and there are no signs of any oil.
Normally wouldn't be.

Internet research says that Rx1 is equivalent to 200. Is that correct?
Not really.

When I connect the red m/meter lead to any 1 of the 3 terminals on the left cap and the black lead to the terminal on the right cap, the reading stays on 1 and doesn't change at all. When I reverse the red and black leads, the reading again stays on 1.
What does your meter say when you put the two meter leads together?

jeff.
 

keno1

Premium Member
Joined
May 5, 2012
Messages
6
Location
Australia
Needle meter is used...especially for microwave stuff...that's all we use.

thanks Jeff, I only have the digital version.


Normally wouldn't be.



Not really.



What does your meter say when you put the two meter leads together?

When I put the leads together, it reads 00.4 or 00.5


thanks Jeff

Ian
 

keno1

Premium Member
Joined
May 5, 2012
Messages
6
Location
Australia
Thanks for making it simple for me Rick.

Set the m/meter to 2000
Touched tthe probes together and reading was 000
Then put one probe on A and other on B - reading did not change at all and continued to show 1
Swapped probes and again reading did not change and continued to show 1

Do you think that means the capacitor needs replacing?
 

rickgburton

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If the meter didn't change, replace it. Use the link jeff1 gave you.
 

jeff1

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What does your meter say when you put the two meter leads together?

When I put the leads together, it reads 00.4 or 00.5
Which is wrong, should read 0.

Then put one probe on A and other on B - reading did not change at all and continued to show 1
Swapped probes and again reading did not change and continued to show 1
For what ever reason it is showing open....only thing to do is swap out the capacitor and forget the meter testing.

jeff.
 

jeff1

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Please do keep us posted :)

jeff.
 

keno1

Premium Member
Joined
May 5, 2012
Messages
6
Location
Australia
If the meter didn't change, replace it.
Here's the latest Jeff and Rick....

Went in to buy a new capacitor today and asked if they could test the old one before I bought the new one. One of their technicians (who does their microwave repairs) tested it and said it was all good and the capacitor was not the problem.

So I will put the capacitor back in and try and figure out what to do next! Would welcome any suggestions or ideas though.

thanks
 

jeff1

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Gonna have to slowly eliminate things ( pull wire off one at a time ) to see what/when causes the fuse/breaker lets go.

jeff.
 
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