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

dave1812March 8, 2014

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.

Thank you for reporting this comment. Undo
dave1812

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).

    Bookmark   March 8, 2014 at 3:01PM
Thank you for reporting this comment. Undo
dodge59

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

    Bookmark   March 8, 2014 at 7:55PM
Thank you for reporting this comment. Undo
dodge59

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

Gary

    Bookmark   March 8, 2014 at 8:18PM
Thank you for reporting this comment. Undo
dave1812

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!!

    Bookmark   March 8, 2014 at 9:12PM
Thank you for reporting this comment. Undo
dodge59

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

    Bookmark   March 8, 2014 at 10:30PM
Thank you for reporting this comment. Undo
dave1812

cool. thx again, Gary!

    Bookmark   March 8, 2014 at 10:40PM
Thank you for reporting this comment. Undo
dave1812

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

    Bookmark   March 10, 2014 at 3:13PM
Thank you for reporting this comment. Undo
dodge59

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

    Bookmark   March 10, 2014 at 3:35PM
Thank you for reporting this comment. Undo
dave1812

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.

    Bookmark   March 12, 2014 at 12:50AM
Thank you for reporting this comment. Undo
dodge59

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

    Bookmark   March 12, 2014 at 10:45AM
Sign Up to comment
More Discussions
self cleaning oven racks
Almost all oven manufacturers require removing oven...
dickross
Wolf oven error on self clean: TCO detect as open
I've had two Wolf E series for nearly 2 years (single...
repac
24" refrigerator. Liebherr, Fagor, LG, etc?
We live in Boston. We are in the market for 24"....
ttkogi
How do you get deals on high-end appliances?
I'm pretty certain that I know what I want for my appliances....
carecooks
good experience with AJ Madison
Got a really good deal on $5k worth of Bosch appliances...
logastellus
© 2015 Houzz Inc. Houzz® The new way to design your home™