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Jenn-air microwave--loud hum; blown fuse...

Posted by dave1812 (My Page) on
Sat, Mar 8, 14 at 14:49

over-the-oven jenn air microwave that we have had for about 11 years, today just hummed for a second and popped the breaker a few seconds after starting a cook cycle.

removed the unit for troubleshooting...

1. If the HV diode is removed from ground, the unit runs, no hum, no heating. (if left in place, the microwave hums the moment i try to run a cycle, blowing the fuse)

2. the HV capacitor has 30 ohms of resistance in both directions. from what i've seen online, the capacitor should be in the range of M ohms resistance, not 30 ohms.

3. the filament of the magnetron tube shows continuity and no short to ground.

the cost of the capacitor is $66. the diode, while seemingly OK when tested with a 9v battery, is so cheap, i'd order one if i order the capacitor.

I have TWO questions:

1. does it make sense that the hum/short goes away if i remove a (what i think is a good) HV diode, and get no heating from the magnetron?

2.if the capacitor IS defective, does it make sense that removing the HV diode, stops the short?

logically, to me, it doesn't make sense that if the cap is bad, that taking the diode out of the circuit would stop the hum/short.


Follow-Up Postings:

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RE: Jenn-air microwave--loud hum; blown fuse...

also, it should be noted that if I ONLY disconnect the magnetron tube, the short is still present (ie, if i leave the HV diode connected, along with everything else).


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RE: Jenn-air microwave--loud hum; blown fuse...

2.if the capacitor IS defective, does it make sense that removing the HV diode, stops the short?

Yep the capacitor is a filter for the diode, on its output,DC
If the capacitor is shorted and it is, if it reads 30 ohms,
(alto you need to remove it to check it for sure)~~ or at least one lead, or if it is a diode bridge, at least 2 leads.

Gary


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RE: oops

Oopsss CRS set in.
Disregard diode bridge comment, should have been remove leg of capacitor to check the capacitor!!!!!~~~sorry bout that.

Gary


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RE: Jenn-air microwave--loud hum; blown fuse...

thanks, Gary. I have pulled the cap out of the microwave and tested it with 2 different meters. both show just 30 ohms.

If I can't find the cap locally, I'm going to call an internet site on Monday and get it on order.

thanks again!!


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RE: Jenn-air microwave--loud hum; blown fuse...

Yep a good cap will show an infinite resistance on an ohmmeter.

All you need is the capacity value and the voltage, and you can go to a higher, (but not a lower value on either).

All you might have to be concerned about is physical size/shape.

Gary


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RE: Jenn-air microwave--loud hum; blown fuse...

cool. thx again, Gary!


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RE: Jenn-air microwave--loud hum; blown fuse...

HV cap on order; arrives on Tuesday the 11th.


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RE: Jenn-air microwave--loud hum; blown fuse...

Anxious to see if it fixes the problem, I suspect a lotta magnetrons have been replaced when it was just a capacitor or diode.

Just like fridges and freezers, they change the compressor when it was probably the start relay or the starting capacitor!, but that's how they make their money, and to tell the truth, most appliance service personnel are not competent enough to component troubleshoot and their bosses would not want them to do it, (even if they could)~~~~~they make more money selling and replacing compressors, magnetrons, etc etc.

Gary


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RE: Jenn-air microwave--loud hum; blown fuse...

The cap came in today, I installed it, and the microwave is back in business! Gotta love when I fix something. :) Been quite a bit of that going on lately. What is going to break next??

Thx again for your help, Gary.


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RE: Jenn-air microwave--loud hum; blown fuse...

Glad to hear it all worked out.

As I said, more than likely a number of magnetrons were probably replaced or even the whole
microwave replaced when all it was, was a simple to replace capacitor.

Gary


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