• ** 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

FIXED Jenn Air JMV8208BAS blows line fuse when vent opens/closes

MIROHO

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17
Location
Connecticut
Model Number
JMV8208BAS
Brand
Jenn-Air
Age
6-10 years
While heating cup of water microwave powered off and vent door remained open. Line fuse blown, replaced fuse, unit restarted, clock set, pressed button to close vent door - fuse blew. Door still open.

Door motor is controlled by two switches. Is it possible that one or both of these switches is the cause? If I remove them and the motor, how do I test the motor?

Motor-Driv by Whirlpool Part Number DE31-10154C
 

MIROHO

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Update, microwave heats up food and the vent door opens/closes. But start the vent fan while microwave is running the fuse blows. Any ideas why?
 

Jake

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Hi,

I will see if Rick can help you.

Jake
 

rickgburton

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Sounds like a door switch adjustment but I don't have the wiring diagram for that model. Can you post a copy of your tech sheet here?
 

MIROHO

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Hi, I made six scanned images as the page is larger than 8.5" x 11". I've only sent Page 03 b/c I believe that is what your looking for. Let me know if you need additional info. Model=JMV8208BAS S/N=16320718NP MANUF DATE= 08/2008

Jen Air Microwave JMV8020BAS Page 03.jpg
 

Jake

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That's very hard to read, I'll ask bigbuck if he has it.

Jake
 

rickgburton

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I'm not sure what "vent door" you're referring to but if it's opening and closing I guess it's good. Will the vent fan motor run normally if the microwave is not cooking? With the vent motor on and running start the microwave. Does the fuse open?
 

MIROHO

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Hi Rick, The unit is a combo MW and Range Hood with a vent fan. It does not vent outside, it vents into the kitchen via a vent, at the top, across the full width. A door covers the vent louvers and is opened via a motor, the Service Manual refers to the motor that pushes the door open as "Louvre Motor". A switch on the control board or a thermo-switch can signal the motor to open the louver door. I can open and close the vent and run the fan through all 5 speeds, (using the control board switches) providing I have NOT turned on the microwave. I've run the microwave for 2 minutes, no issues there. Then, while the MW was running I started the fan and the fuse blew (opens). Hope this helps.

Many thanks, Michael
 

rickgburton

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... the motor that pushes the door open as "Louvre Motor".
Gotcha...that's what I needed. OK I'll assume we're talking about the 20 amp ceramic fuse that "blows" and that you're replacing it with the same. Measure the resistance of the vent motor. If it's 30Ω (± 2Ω), replace the main board:

Control Board WPW10127101
Control-Board-WPW10127101-01608951.jpg
 

MIROHO

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Hi Rick, please excuse my ignorance. When testing the motor's resistance am I correct to assume the following:
- Disconnect power cord
- install new fuse (20A ceramic - Bussmann ABC Series) . Which is what I've been using.
- When testing do I disconnect the motor or leave it connected and squeeze the probes in?
- Or should I disconnect the motor and test the power input wires?

What has me confused is that if I am testing the motor's resistance how does that prove the board is good or bad?

Many thanks Michael
 

MIROHO

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UPDATE: just realized the MV did not heat up the cup of water. Tested the three door switches and they are OK. So, is it the magnetron or, something else, or two things like the diode?

Many thanks, Michael
 

MIROHO

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UPDATE 2: I removed capacitor test continuity and meter gave audible beep. Does that meed the Cap is no good?
 

rickgburton

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How to test high side components:
C-HV Testing.jpg

Less expensive meters may not have the ability to test the capacitor or diode. Use a 9 Volt battery:
C-HV-Capacitor Test.jpgC-HV-Diode Test.jpg
 
Last edited:

Jake

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Thanks Rick and bigbuck for helping MIROHO on this microwave.:)

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.

Jake
 

MIROHO

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With DMM set to diode testing - Diode - .OL I assume it's OK

With the DMM set at 200 (audible) I get the following readings:
Magnetron 0.1 Audible sound - I assume it's OK
Capacitor 0.1 (down from about 3), Continuity tested across terminals - Yes (audible sounds) I assume it's OK
HV Trans Primary = 0.1, Filament = 01, audible sounds in both cases. I assume it's OK.
I could not figure out how to test and get a reading on the secondary windings.

The "Bottom Thermostat" did not give a positive reading when tested for continuity, the adjacent "Hood Thermostat" did test positive (audible sound).
Per the Component Testing Procedure:
Bottom Thermal Cut-Out (Thermostat)
Disconnect all wires from TCO.
Measure resistance across terminals. ........
Non–resetable.
Open: ....... 248° F (120° C).

Is it possible that this bottom thermostat is the cause?

Many thanks for putting up with my ignorance. And, I have to say that I know more each day, which is a rewarding experience.
 

rickgburton

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With DMM set to diode testing - Diode - .OL I assume it's OK
On the diode function the diode should show continuity (closed) then reverse the test leads and the diode should show no continuity (open).


Capacitor 0.1 (down from about 3), Continuity tested across terminals
Set your meter on Rx10K ohms (10,000Ω). Measure across the two terminals. Your meter should show several thousand ohms and fall back to ∞ (open or 1). Set your meter to the lowest ohms setting Rx1 and measure from each terminal to the capacitors metal case. Your meter should show open or ∞ or 1.


I could not figure out how to test and get a reading on the secondary windings.
Set your meter on the lowest ohms scale Rx1. Remove the secondary wire from the HV capacitor. Measure from the secondary wire to the metal body of the transformer or one of it's mounting screws. Your meter should between 60Ω and 120Ω

The "Bottom Thermostat" did not give a positive reading when tested for continuity, the adjacent "Hood Thermostat" did test positive...... Is it possible that this bottom thermostat is the cause?
No, One thermostat is a normally open thermostat. It closes at a set temperature.

Earlier (post #13) you said:

Tested the three door switches and they are OK.
Test the switches by opening and closing the door. Don't just push the switch button.

It's starting to get a little confusing with this machine so where exactly are we ?? Are we troubleshooting a non-working microwave or a vent motor that blows a fuse or both. If you want to know if one of the high side components is bad you need to know if there's 120 VAC across the two primary terminals on the transformer. If there's 120 VAC going to the transformer one of the high side components failed. If there is less than or 0 VAC going to the transformer the problem is elsewhere.
 

MIROHO

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Hi, before I start testing I'd like to point out that my DMM does not have the Rx settings you refer to. It have 2M, 200K, 20K, 2K, 200 (AUDIBLE). So my lowest setting is 200, correct? See attached image of DMM Commercial Electric MS8301A DMM.PNG. So how does my setting relate to your settings? (Black probe in COM, Red probe connected to the Red Opening to the right.

I removed the three door switches from the unit and tested them. I see you recommend testing while they are in the unit. Makes sense as maybe the door latch is worn and not applying sufficient pressure.

Last time I blew (opened) the 20A main fuse I had the microwave running, with cup of water inside the unit, and water never got hot. While the MV was running I turned on the vent fan and that is when the 20A main fuse blew (opened).

Sorry for making this so confusing and appreciate your patience.
 
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