Any of you monitor guys fixed a microwave?

Tighe

Well-known member
Joined
May 25, 2009
Messages
20,797
Reaction score
825
Location
Richmondville, New York
I have a Whirlpool over the range microwave that I have had for about a year and a half and it has stopped heating.

I checked the voltage to the transformer and it is getting 120v like it should, so that means that the problem is with one of the following:

High Voltage Capacitor
High Voltage Diode
Transformer
Magnetron

I am using the instructions in the service sheet inside the microwave to test each of the components.

Transformer:
I believe that the transformer is correct as I am getting the proper resistance on both ends, although I have never seen a transformer with 3 leads on the output side.

Magnetron
I made a mistake when I first started looking at this, I disconnected the leads and forgot which goes where. The case has FA and F on opposite sides of each terminal on the magnetron but I don't know what that means. Are magnetrons polaric? I would think so based on that they run on DC or Pulsed current. One terminal is the filment can anyone help me figure out which is which? I think that it is fine though.

HV Diode
This is pretty much impossible to test with my craftsman meter, both ways read 1 ohm (is that infinite?) If I use a 9v battery I get 6v one way and 2v the other way. I am thinking it might be bad?

HV Capacitor
This I am supposed to set the meter to the Rx1000 scale (I did 2000 as there is no 1000 scale on my meter). Normal for terminal to terminal is momentarily indicates several ohms, gradually returns to infinite. Terminal to case is supposed to be infinite resistance. I get 1 ohm reading both ways, same as if the probes were not touching anything.

A replacement HV capacitor is $55 so I don't want to toss out money like that if it won't fix it. Also, if I don't figure out the proper polarity for the magnetron I will be afraid to power it up as I will probably fry it in the process and waste $55 plus shipping.
 
Check All of the door switches. There are at least 2, sometimes 3 or 4. Every microwave I have repaired has been a blown fuse or a bad door switch. Conveniently, they are usually just micro switches like we use on buttons.
 
Connected to the input of the transformer:

20130120_144308.jpg


Set it to a few seconds and got 120v

20130120_144337.jpg
 
There is a fuse in there too somewhere...

Check All of the door switches. There are at least 2, sometimes 3 or 4. Every microwave I have repaired has been a blown fuse or a bad door switch. Conveniently, they are usually just micro switches like we use on buttons.

If you look at the following post you can see that the transformer is getting 120v, that is after all the safety interlocks and fuses. The problem is in one of the components I listed above.
 
That HV cap can kick your ass, be careful. Usually it's the magnatron but some of those microwaves have sensors in the cabinet that open up and stop it from working. Could be one of those. I also think there is a door safety switch that can go bad and keep the thing from working. It's been awhile since I worked on those so I can't remember all the details.

Microwaves are a pain in the ass ( and can be dangerous ) to work on. Be careful.

Edit: Don't run it empty either, put a glass of water in there.

Double edit: What Smoke and Lights said, some have several cabinet fuses and you have to look at the schematic to see them, it still can be hard to tell exactly where they are. You have to take the thing apart to find them and meter them.
 
Last edited:
Check Thermal cut off first!!!

Your Lost!!

If not fixed yet

u need to unplug the microwave completely

Put the wires back on the transformer

anyway but loose!!

either way just get them back on...


then ohm out the thermal cut off switch i see two in the picture!!

one is on the magnatron the other is on the frame on left side of picture..



post the ohm
 

Attachments

  • th.jpg
    th.jpg
    8 KB · Views: 35
Things to think about

When go to use a mircowave you set the time and power

or you just set the time..

Ok on power 10 for magnatron it will turn on and stay on..

if its set to power of 5 it will turn magantron on a few seconds at a time

over the timed minutes..

Another click can be heard before the magnatron is working

and the display and lights will all be working which is the way its

look as of now.. let us know if you hear a relay click????

the relay on the control board close's the relay and allows voltage

the the big transformer in the rear of cabinet..

so you should hear a relay click when the magantron should start

no click heard from relay on the control board then theres a different issue

mirco switch would be dc voltage going in and out the control board only.\
in that case the light or timed display should not be working just a tip!

if you remove the control i can show you the relay..if needed

the thermal cut off should have maybe 50 120 ohm cold

dont worry about the ohm if bad it should read open..

and you dont need a thermal cut off switch to continue testing the microwave.

simply jumping it with a jumper wire will get you down the line to test others

things..what have you done so far?

a symptom for a bad magnatron has a humming noise and no heat..

if left on under this condition you will explode the diode that is connected

to the mangnatron cap..getting shock is very easy!!! when voltage gets to

the cap dont measure any voltage with your volt meter it some how just gets you

and barley touch it with the meter...the magantron does run on dc

Need to inspect the diode for a crack as well.. I would be using a high voltage

probe the test any dc at the cathode of diode..

Your control maybe working correctly im just reviewing the procedure
of one thats working..odds are its
the magnatron and the thermal cut off the thermal cut off protect the
magnatron and opens the ac ciruit..

But if the diode is bad it will not allow dc to the magnatron and it wont

heat up..the food.




You should discharge the cap first!!!

Discharging a high voltage capacitor
Discharging your microwave's capacitor is absolutely essential in preventing injury to your microwave, your tools, and yourself. A capacitor stores large amounts of electricity even when your microwave is unplugged, and it must be discharged before beginning any repair.

A capacitor is discharged by creating a short circuit between each of the two capacitor terminals, and between each terminal and the chassis. The chassis is the metal mounting (bare metal surface) of the capacitor. Read these directions thoroughly before you proceed.

With your microwave unit unplugged, touch the blade of a well insulated screwdriver to one terminal. Gently slide the screwdriver forward until it reaches the other terminal, holding it there for a few seconds. Be aware that this often results in a loud and startling 'POP'.

Repeat this procedure in order to create a short circuit between each capacitor terminal and the chassis (bare metal mounting plate surface). This same method can be applied to a capacitor having three, and not two, terminals.
 
They moved the forums and you have to pay $45 a year to post?!

Huh? That's news to me. Everything was free before.

This is in their FAQ now:

"You can participate in this forum absotootly free! But if you'd like to unlock the enhanced features, such as editing your own posts, posting in an existing topic, sending private messages, and viewing the thousands of illustrative attachments you'll need to become an Apprentice Appliantologist-- see this page for details."
 
Tighe said:
I believe that the transformer is correct as I am getting the proper resistance on both ends, although I have never seen a transformer with 3 leads on the output side.
Very common. It's called a centre-tap transformer.

Tighe said:
This is pretty much impossible to test with my craftsman meter, both ways read 1 ohm (is that infinite?)
Absolutely not. There is a decent guide on testing a HV diode here: http://www.repairfaq.org/REPAIR/F_micfaq5.html#MICFAQ_003

Finding the polarity of the magnetron shouldn't be difficult. Look at a service manual of any microwave and look at what it is connected to.

With all due respect, some of these questions make me wonder if trying to repair this is a good idea. Please be careful.
 
Very common. It's called a centre-tap transformer.


Absolutely not. There is a decent guide on testing a HV diode here: http://www.repairfaq.org/REPAIR/F_micfaq5.html#MICFAQ_003

Finding the polarity of the magnetron shouldn't be difficult. Look at a service manual of any microwave and look at what it is connected to.

With all due respect, some of these questions make me wonder if trying to repair this is a good idea. Please be careful.

Thanks Hewitson, that link was very helpful!

Also, I am not an idiot. I just disconnected the mangetron and forgot which wire went on which terminal, I think we have all been there before.

Secondarily, I have never worked with any of there components before, be we have to start somewhere. I won't hurt myself. I knew to discharge the capacitor first.
 
I too think you'd be better off just replacing it. god forbid it blows up later on or starts on fire (we know how you love your fire hazards ;-) )

I do wish you luck tho!

worse comes to worse you have a nice metal casing you can use for just about anything :)
 
I too think you'd be better off just replacing it. god forbid it blows up later on or starts on fire (we know how you love your fire hazards ;-) )

I do wish you luck tho!

worse comes to worse you have a nice metal casing you can use for just about anything :)

When a new over the range is $200 I can't justify spending $120 for a new Mangetron or $55 for a new HV Capacitor. $6.50 for a new HV diode I can though.
 
My over-range microwave stopped heating, turning, etc after a big power outage. Everything checked out. I pulled the wires out of the connectors to the controller board and cleaned them one-by-one and reseated. Microwave started working again...
 
Did the thermal cut off's check good??

Did anyone read my first post?

I connected to where 120v goes into the transformer. That is after all the sensors, interlocks and fuses. I got 120v. Everything up to that point is working. So it is one of the 4 things i listed.
 
Back
Top Bottom