• ** 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
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WMH3205XVS Arcing

RichardK

Premium Member
Joined
Jan 15, 2018
Messages
3
Location
Madison, WI
Model Number
WMH3205XVS
Brand
Whirlpool
Age
6-10 years
Greetings, my first post here.

This is frustrating. Major arcing inside the waveguide. The magnetron is completely clean and shiny. The source of the sparks is a small nub inside the waveguide, about half way down (this is a bent rectangular waveguide about seven inches long). It's some part of the waveguide whose function I'm not aware of. It's the size of the tip of my little finger, attached inside the waveguide with a single screw with an insulating bushing (verified with ohmmeter).

When the machine is running this part arcs to the waveguide and little bits of metal drop to the bottom of the waveguide. I have attached a picture of the part itself taken with an inspection camera (ignore the date, the clock in my inspection camera was not set) and a second picture of the screw and washer which are its attachment point to the waveguide. It appears to me that the arcing is causing metal from the waveguide to deposit on the part. The picture is from the top of the waveguide through the magnetron port. The opening to the oven cavity is visible at the bottom, with the cover removed.

Anyway, I'm thinking this unit is a loss, because this is inside the waveguide assembly, which is riveted together and then riveted into the chassis. Any suggestions welcome, or even an identification of the function of this part.

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RichardK

Premium Member
Joined
Jan 15, 2018
Messages
3
Location
Madison, WI
Arcing, continued

Guess I'm not surprised nobody replied, this is pretty weird.

I managed to get the part out. I bought a pair of 12 inch curved forceps and just managed to grab it. As I said before, this part was mounted inside the waveguide and it's the size of a finger tip. What I didn't know is that it's made of carbon (apparently) with a metal cap. It was screwed to the inside of the waveguide. As you can see from the attached picture it's in bad shape. After I removed this part the microwave functions normally, no arcing. But there must have been a reason for putting this part in there - some clever bit of engineering to get the RF to go around the corners in the waveguide - so I'm a little leery of running without it. It looks like a $2 part but I don't see it in anyone's parts list.

Also, I measured the temperature of the magnetron heatsink with an IR thermometer. It reaches around 350 degrees F. Anyone know if that is in the normal range?

It would really irk me to have to replace this unit because a passive part failed.

IMG_20180122_182406599.jpg
 
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Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
105,112
Location
McMullen Valley, Arizona
I'll ask Rick to see if he can assist you.

Jake
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
36,343
Location
Murray, Utah 84107, United States
I've never seen one before but it must have something to do with interrupting the microwaves before they enter the cavity. Did you try it with that part removed?
 

RichardK

Premium Member
Joined
Jan 15, 2018
Messages
3
Location
Madison, WI
Rick,

Thanks for your reply. Yes, the microwave works without this part, no arcing. My main concern is whether removing it will make the magnetron run hotter. That could be the case if the part was there to improve the SWR in the waveguide. As I mentioned, I measured the operating heatsink temperature of the magnetron with an IR thermometer and it seemed really hot, around 350 degrees F. But I'm having trouble finding any numbers for what a normal heatsink temperature is.

The other possibility that occurred to me - basically this part is a little antenna connected to ground through a resistor. It's about 1.5 cm long so it would be a quarter wavelength at around 5 GHz. I wonder if its purpose is to reduce interference with 5 GHz Wifi. Maybe this design had a harmonic that interfered with other devices.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
36,343
Location
Murray, Utah 84107, United States
I've been repairing microwaves, both commercial and domestic, for more than 30 years and that's the first time I've seen anything like that. I don't see it on any of the parts diagram so leave it out. If it works fine without it, it works.
 
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