• ** 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

rickgburton

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10K scale is the same as the 20K scale. 200 is the lowest scale. OK, we have a microwave that runs but that doesn't heat and a vent motor that blows the 20A fuse when turned on. Ignore the vent motor for now but disconnect the vent motor connector. Check the door switches again (opening and closing the door). If they test good restore power and set the machine on high for one minute and measure the voltage at the primary side of the transformer.

Did you know new OTR microwave combos start at <$100.00 ??
 

MIROHO

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On a whim I checked the HV fuse, it was NG, so I replaced it.
Diode = reads OL (Open Loop) in both directions
Cap = goes to 0
secondary wire = 120
the three door switches are OK, as per the switch chart

The fan works, the vent door motor works and the hood light works, and all at the same time.

Open and close the door and the trans fan spins for a second.

Interior light works as does the table motor.

Start the microwave feature and the main fuse blows in a second. Could the cause be the diode?

I need to repair this one as it matches with the other appliances. Otherwise I would replace it.

Thanks, Michael
 

rickgburton

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I see you're having a difficult time following my instructions. What's an HV fuse? According to your measurements the diode is bad, the capacitor is bad and the secondary windings in the transformer is on the edge of being bad at 120Ω.

Go back and read my last post again and you better tell me what this switch chart is you speak of. I have a gut feeling you're not checking the switches correctly. Then follow my instructions in the rest of the post. Let's get the switch thing sorted out first.
 

MIROHO

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OK, tonight, I'll go back over your instructions and this time focus on the three door switches. Any nothing else.

For clarification; on Sept 12 @ 10:28 PM bigbuck posted two .PDF files Tech Sheet and Service Manual and I have been using them as reference.

The HV fuse: this unit has two 20A ceramic fuses, one 120V - labeled Fuse (20A) and one 250V labeled H.V. Trans Fuse. See the tech sheet, page 1 schematic diagram.

The "Switch Chart" is on the tech sheet bigbuck posted, page 2 upper left corner. This is what I used. I followed those instructions along with your instructions. I left the three switches mounted in place. For each of the three switches I disconnected the wires, set meter at 200Ω with audible, opened and closed the door. If I got an audible sound I took that as a Positive if I did not I took that as a Negative as per the Switch Chart. In every case I saw the switch button properly depressed.

I do appreciate your patience and willingness to teach me.

Thanks, Michael
 

rickgburton

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LOL, I didn't see that chart the first time I looked. I only looked at the schematic. Look at the tech sheet under "high voltage components" Transformer. You said your meter showed 120Ω on the secondary wire to ground and it should only be 90Ω (±2%). So we can add bad transformer to the list of bad parts. Then go to the bottom under diode and read what it says right under it. Now I'm questioning your meter's capabilities. What's the brand and model of your meter?

You don't need to do any more testing. I think I have enough information from the clues in your posts to figure out what happened. The high resistance on the secondary windings most likely shorted the capacitor causing high current draw through the control board causing one of the relays contacts to stick closed when it should be open. The only thing the vent motor and microwave have in common is the control board. Keeping in mind the vent motor works OK when the microwave is off and the microwave works OK when the vent motor is off so with a stuck relay, if you turn the fan on while the microwave is running or turn the microwave on while the fan is running is like shorting L1 and N together and there goes the fuse. The control board needs to be replaced and the transformer needs to be replaced and maybe the capacitor and diode. I would retest the diode and capacitor if I was you.
High Voltage Transformer DE26-00125A
High-Voltage-Transformer-DE26-00125A-01308694.jpg

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

High Voltage Capacitor 8206562
High-Voltage-Capacitor-8206562--01682050.jpg

Diode DE91-70063D
Diode-DE91-70063D-05081134.jpg
 

MIROHO

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Hi, DMM is Commercial Electric MS802A, uses 2 pen light batteries, it's brand new. Maybe I need to by a better quality meter?

I do know that when the microwave died the first time there was a bit of a pop.

One correction to your statement "...and the microwave works OK when the vent motor is off...". The microwave does not work. If I recall correctly, last night, when I started the microwave, while nothing else was on (except interior light), it blew the fuse.

Well this ain't going be inexpensive, that's for sure. Since the control board is still working would it be safe to replace only the other three components? Somehow I believe the answer is no because the relay is on the board and there really isn't a way to replace a board relay.

Once again, thanks for the help. This has been one heck of a learning experience.

Michael
 

rickgburton

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....when I started the microwave, while nothing else was on (except interior light), it blew the fuse.
Isn't this a new development?? It was working (although not heating) without blowing the fuse. That keeps bringing me back to those door switches.
 

MIROHO

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Correct, it is a new development, and I just now tried it again, same results, immediately blew the 120/20 fuse. HV Trans fuse is still good. So, assuming you are correct, that a door switch is faulty, such that the fault is intermittent, which one is it, of the three?


Many thanks,
Michael.
 

rickgburton

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The monitor switch, also known as the deadman switch, is a normally closed switch with L1 on one terminal and Neutral on the other terminal. There's power at the switch only when the door is closed. It's more of a safety switch that keeps the high side from operating if the door is open by creating a dead short and blowing the fuse. Sometimes the switch holder or latch mechanism gets out of adjustment (there's very little) and when the door is opened the monitor switch closes before the primary switch can interrupt the voltage then "boom" fuse opens. The microswitch has three terminals but manufactures will often leave off the one not used. A common mistake is switching the monitor switch with one of the other switches or if the switch has three terminals and only two wires, putting the wire on the wrong terminal.

To keep from doing a lot of unnecessary testing and to make diagnosing easy, you need to organize your tests. If the microwave runs but doesn't heat or if it blows the fuse when you start it, you need to break the system down to the low voltage side and the high voltage side. Let's say the microwave runs but doesn't heat. Check for 120 VAC on the primary side of the transformer. If your meter shows 120 VAC at the primary side of the transformer then you know the problem is going to be one of the high voltage components. Let's say it blows the fuse when you press start. Again, start by breaking the system in two. Disconnect the wires on the primary transformer terminals. Tape the ends if needed. When you press start if the fuse still blows you know all the high voltage components are good and the problem is in the low side. If the fuse doesn't blow you know the problem is one of the high voltage components. Are you catching on yet? Here's a microswitch diagram that may be helpful:
Microswitches.jpg

I forgot to add, the same thing applies to the vent motor. If there's a problem when the vent motor is turned on, eliminate it from the circuit by disconnecting it. Now turn it on and if the problem is still there, it's not the vent motor. Problem goes away with it disconnected, bad vent motor.
 
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MIROHO

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With everything connected and 2 good fuses installed.
As a first step I removed, cleaned terminal connections, tested and put back every switch. One at a time.
Then while switches were installed in place I tested them with door open and closed.
Top / Secondary switch, normally open, tested OK
Middle / Monitor switch, normally closed, tested OK Only has 2 terminals and connects only one way.
Bottom / Primary switch, normally open, tested OK
Carefully checked that switches were properly seated, connections good, door latch properly operates and latch properly depressed the orange switch tab. All good.
Now I've rule out the switches and door latches

Open door interior light goes on
Started vent - motor and vent fan OK
Turned on cook top lamp OK
Turned on all three no problem. So, 120 VAC is OK.

Disconnected wires on primary side of transformer, started and ran MV for 30 secs no problem, interior light stayed on, table rotated, vent worked. Fuse did not blow. So now it has to be on the HV side.

Started MV, with primary wires connected to HV trans, and fuse blew (one on right - not the HVT Fuse).
JMV8208BAS Fuses.jpg

Checked following:
Diode - Set DMM on diode no reading either way - so this is no good.
Cap - tested with 9V battery (DMM set @ 9VDC) read less that one volt, and zero resistance - so this is NG
HV Trans Primary less than 1 Ω.
Filament less than 1 Ω
Secondary no reading
HV Tans is no good?

So now I am back to where I was earlier (Sept 18).

Since the control board is still working could I only replace the other three components and not the control board?

Is there a way to test the control board relays?

Once again, thanks for the help.

PS, I believe I'm catching on. :)
 

rickgburton

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I believe you are too. The control board is fine and the problem is one of the high side components or more than one component. Your meter can't measure the diode. It doesn't have enough voltage. A microwave diode is actually four diodes set up as a bridge rectifier.

Your meter can check a single diode but not a bridge rectifier. You can use your meter to check the diode with a 9V battery. It's rare to find more than one part failed at the same time. You had a measurement on the transformer secondary before (120Ω).

I don't know why you don't have anything now. I think the mag tube is good, the transformer is good and the diode is probably good. I think you just need an HV capacitor (or a better meter...LOL).
 

MIROHO

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Hi Rick, just wanted to follow up on this. Today I replaced the capacitor and the microwave now works as it should. Many thanks for your patience, guidance and willingness to help. I did not reply sooner because the part was on back order and did not arrive until this past Thursday.

Now, believe or not, the range top ignitor keeps is clicking; but only with three of the burners. Had this problem in the past, had to clean the ignitor switches. Seems that they get gummed up.

We've not been too happy with the Jenn Air line of appliances. Bought them in 2008 under the premise that Jenn Air is above average in quality. Not true.

Best wishes and again many thanks.

Michael
 

rickgburton

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Glad to hear you got it fixed. Jenn Air was bought out by Maytag years before Whirlpool acquired Maytag. It's basically a Whirlpool.
 

MIROHO

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Hi Rick, a new problem with microwave. Within a few minutes or immediately after starting the unit it powers off, screen goes black. If I play with the door (open, close repetitively, and with a bit of force the power is restored). I tested the three door switches and they work, though the bottom one - primary interlock sw - does have a considerable carbon build up. Hoping it is not the Control Board as that is costly and several places are out of stock.

Per manufacture service manual.
Troubleshooting Table
Symptom
Microwave oven does not work, no display, fuse is OK.
Cause Correction
1. Open or loose wire harness.
2. Open thermal (magnetron) cutout.
3. Open low voltage transformer.
4. Defective PCB assembly.
Correction
If thermal (magnetron) cutout is defective, check fan motor.
If low voltage transformer is defective, check PCB assembly.
 

rickgburton

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Check the door switches by opening and closing the door. Sometimes the switch bracket gets out of adjustment. Some have an adjustment and some don't. If the door switches are good, it sounds like a broken solder joint somewhere on the control board. The door switches don't usually affect the display or supply voltage to the control board. If the display goes blank the voltage is interrupted somewhere on the board

WPW10127101 Asy Pcb Parts
whirlpool-asy-pcb-parts-wpw10127101-ap6015392_01_m.jpg
 
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