Microwave Stirrer & Turntable Motors Are Toast

Thread Starter

Mr_Dean

Joined Dec 28, 2017
8
GE Spacemaker JVM1441BH04 measures 24.7 volts AC coming off the cooling fan, but both the stirrer motor leads and turntable motor leads (with motors disconnected) measure approx 97 volts AC. Is there a component between the fan motor and the other two motors that is no longer providing the correct 21V AC??

Excellent photo's of cooling fan terminals posted by Senior Member "debe" in much earlier thread:
https://forum.allaboutcircuits.com/...ngine-from-dismantled-microwave.120754/page-1
 

dendad

Joined Feb 20, 2016
4,215
It looks like the fan motor is also used as an auto-transformer to provide 21VAC for the stirrer and turntable drive motors.
With the 2 x 21V motors disconnected, does the fan motor still run?
It could be the fan motor has an open circuit. Disconnect the fan motor and measure the resistance between all the wires for a start.
 

Thread Starter

Mr_Dean

Joined Dec 28, 2017
8
It looks like the fan motor is also used as an auto-transformer to provide 21VAC for the stirrer and turntable drive motors. With the 2 x 21V motors disconnected, does the fan motor still run? It could be the fan motor has an open circuit. Disconnect the fan motor and measure the resistance between all the wires for a start.
Thanks "dendad". Yes, with both 21V motors disconnected, the fan motor still runs. I'm hoping the background story pasted here from my Fixya post will help with my specific dilemma:

GE JVM1441BH04 Over Stove Microwave: Safe to reconnect replacement stirrer & turntable motors after accidentally burning out the turntable motor? Tapping noise was coming from the 21v AC stirrer motor which sits atop the cooking chamber. I disconnected the two connecting leads, unfastened the single screw holding it on, placed in on my scanner glass to get a high rez photo of all the specifics listed on the motor label. Bad news: While waiting for the scan to finish, I warmed my coffee in the microwave on the highest heat for 30 seconds. I subsequently discovered the 21v AC turntable motor, which had been working just fine, was now no longer working, with infinite resistance across its terminals, and a burnt electrical smell. Both the stirrer and turntable motors are powered by a 24v tap off the magnetron fan. My theory: By running the microwave with the stirrer motor out of the circuit, I delivered excessive voltage to the turntable motor, which quickly fried. The 24v tap off the magnetron fan motor currently shows the correct 24v output. However, with both the stirrer motor and turntable motor disconnected, running the microwave for a few seconds shows approx 95v across the wire leads for both of the 21v motors. I have obtained replacement motors for both the noisy stirrer motor and the fried turntable motor. My question: Can I simply reconnect both motors in their proper locations, vow never again to run one without the other connected, and all will be well? Or will the newly installed motors simply be fried in a matter of seconds?
 

dendad

Joined Feb 20, 2016
4,215
It looks like the reading is normal. And just make sure both motors are always connected.
But it looks a bit odd to me. I would have thought the volts will be more stable than that.
 

BR-549

Joined Sep 22, 2013
4,928
Yes there is. It looks like a variable resistor. See if you can eyeball it for condition. I wouldn't try to adjust it just yet.
 

Thread Starter

Mr_Dean

Joined Dec 28, 2017
8
Do you see it?
Sorry BR-549, I'm afraid I don't know what to look for ("variable resistor"), other than the usual multi-colored cylindrical components.

The turntable motor has a lead connected to the microwave control panel circuit board, which shows 0.1 ohms between the turntable lead and the nearest side of a 3 amp power relay, labeled on the board as “RY088 T/TABLE” All surfaces of this component appear intact, and identical to 3 other adjoining components. I’ve attached the best resolution image I could find online of the control panel board (GE part #WB27X10871, labeled RAS-OTR7HV MAY 31 2005 DE41-00309A). Photo is also available here: https://www.ebay.com/itm/GE-Maytag-...809487?hash=item27e7732c8f:g:BwoAAOSwAuNW42Po

If you can point me in the general area of the board where I might find the variable resistor, I would be much obliged.
 

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BR-549

Joined Sep 22, 2013
4,928
OK....to the left of the 3 is a potentiometer symbol connected to the relay contact. Find that pot and check it out. The ground return for the high voltage coil goes thru this pot at the start of tube. It shows a pot on the image........but it might be a fixed resistor. It looks like the lamps and motors ground thru this at start-up too. The inrush relay....then the ground switches and goes thru sec relay. The image shows a pot....but might be fixed and indicating different values for different coils.

Until sec relay kicks in.....ground return is thru the resistor.
 

BR-549

Joined Sep 22, 2013
4,928
I read the thread you referenced in your first post. There is another reason to supply other loads thru motor winding tap. It can be used as an interlock. Although I don't see that purpose here.

But in other configurations.....if the motor fails......then the other stuff doesn't power up. Built in safety.
 

Thread Starter

Mr_Dean

Joined Dec 28, 2017
8
I read the thread you referenced in your first post. There is another reason to supply other loads thru motor winding tap. It can be used as an interlock. Although I don't see that purpose here.

But in other configurations.....if the motor fails......then the other stuff doesn't power up. Built in safety.
Thanks for taking my question seriously BR-549, and for providing substantial replies. Out shoveling snow early this morning and I'm fading fast. Will return to this as soon as able, hopefully within the next day or two.
 

BR-549

Joined Sep 22, 2013
4,928
Ok.....hope that helps....that's all I got. Don't know the relay sequence....and it could be different for different modes.....like defrost. But be aware of it when measuring voltages. You can always jump the motor grounds separately to test.......be careful.
 

ymg200

Joined Oct 2, 2015
41
I got a similar problem in GE Spacemaker XL-1800 microwave (model JVM1860). Everything seems working in the microwave except turntable, cooling and stirrer motors. I checked that stirrer motor doesn't get the voltage; other two motors likely too. I see that these three motors have common circuit. I have attached the schematics for my microwave, circled these three motors.
Is there a known issue that faults the circuit of these three motors?
 

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