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Need help repairing Microwave oven

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Ensing

Aug 25, 2021
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I've a extra-large, 30-year-old, 'National' Genius microwave oven.
It is only partly working.

And I'm in COVID19 Lockdown in New Zealand.
Can anyone help me to diagnose the fault(s)?
I have no electrical or electronic training and
don't expect to be able to fix it.

However, I have tools. And perhaps you could ask me
questions that could help you to diagnose possible
reasons for the fault(s).

So I'm hoping for your expert help to diagnose the fault in the microwave over Lockdown as the family need it. If it is not-repairable, I'll buy a new one online. But I'd rather have this old one repaired.

It is large and made with quality.
And no repair shops are able to be open - deemed non-essential.
Can you, forum members, talk me through a diagnosis
and possible repair?
 
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DBingaman

Jun 27, 2021
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Check out this video, might help. You will at least need a DMM at minimum to troubleshoot with:

 

DBingaman

Jun 27, 2021
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Just a note on the video.....I would not recommend any type of live testing especially since the Op has identified his electrical knowledge as zero.
True, the Op has no experience in this arena. Microwave ovens have high voltages present. Now that the subject is brought up it is probably not a good idea for the Op to try to fix the microwave on his own.
 

VenomBallistics

Aug 30, 2018
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Noob + MOT = Much bad joo joo.
Our advice should be limited to those operations not involving these parts.
One flash, you're ash is in full effect.
You are where seasoned techs fear to tread
 

Ensing

Aug 25, 2021
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OK. I'll hope for a fault diagnosis? Perhaps that's possible.
I have an entry level DMM. Still, I'm unqualified.

I've fixed the drive previously. There's a belt that drives the turntable. I had to make a replacement. The motor was still good. I used a record turntable belt of similar size and had to tweak it to fit. A bit McGyver though. It has worked for 2 years since that repair.

However, this is more than that. The turntable is not working. The fan is also not working.
But the microwave still heats food. I'm unsure if this is safe.

Steams up the oven. And no rotation. So manual rotation, stirring or shifting of the food seems to address this issue.

I do hear the Hum of the transformer for the magnitron.

OK. Having watched the video, I see that there can only be several of 100 things malfunctioning. So diagnosis seems to require a lot more work that I anticipated.
 
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VenomBallistics

Aug 30, 2018
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We get to stay away from big sparky then .
Are these independent motors for the fan and turn table? Or do they share a common motor
 

VenomBallistics

Aug 30, 2018
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you do need the fan at least. turn table is nice but optional.
given the nature of the stuff in such an appliance, a policy of no live testing while disassembled is prudent.
that said, trace the wires back from the motor(s) and see if you have blown fuses, tripped breakers or outright burnt stuff.
Also, if you have an ohm meter, check the motor(s)
take pictures and share along the way
 

flippineck

Sep 8, 2013
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Is there a potential danger from stored charge even after the unit has been unplugged for a while?
 

Externet

Aug 24, 2009
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First remove the fuse while unplugged and check if good continuity *
Being that old perhaps has no electronic display nor panel buttons, just a timer knob. Is that right ? Does the light inside work when opening door ? *That would mean a healthy fuse.
The moment it failed did you stopped by opening the door or did you turn off by canceling its timer ?
 

CircutScoper

Mar 29, 2022
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However, this is more than that. The turntable is not working. The fan is also not working.
But the microwave still heats food. I'm unsure if this is safe.
It seems unlikely that any fuses, relays, or interlock switches exist that would block power from the turntable and fan while still letting the magnetron run. So my guess is that age, use, and moisture have caused a simple connector or splice to corrode and fail somewhere in a circuit path common to these two motors, but separate from the power connections to the magnetron.

Therefore...

With the oven safely unplugged, I'd start tracing continuity with your ohmmeter from the timer terminals to the motors. I think you'll find the break.
 

Alec_t

Jul 7, 2015
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Guys, the original post was Aug 2021. It's likely the issue has been resolved/abandoned.
 

davenn

Moderator
Sep 5, 2009
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First remove the fuse while unplugged and check if good continuity *
Being that old perhaps has no electronic display nor panel buttons, just a timer knob. Is that right ? Does the light inside work when opening door ? *That would mean a healthy fuse.
The moment it failed did you stopped by opening the door or did you turn off by canceling its timer ?

You didnt read the earlier post ;)
the oven still heats


As @Alec_t say, this is an old thread

I am closing it
 
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