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Microwave Making Buzzing Sound [Sound Clip Included]

Discussion in 'Repairing Electronics' started by ParkingLotLust, Aug 21, 2009.

  1. ParkingLotLust

    ParkingLotLust Member

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    For the last week or so, our microwave (a ~6 year old Panasonic model) has been making this sound when its first turned on. If its left for an hour or two, the sound happens for longer. If you stop it and start it, the sound is short. Does anyone know whats happening? Sounds almost like an arcing? Is it dangerous to leave it like this (ie. will it just die, or will it violently explode killing everyone in a 10km radius?)

    Thanks!

    The attachment is a zipped mp3 file.
     

    Attached Files:

  2. HarveyH42

    HarveyH42 Banned

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    I didn't hear anything unusual. Mine is much louder.
     
  3. ParkingLotLust

    ParkingLotLust Member

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    The chirping, buzzy sound right right at the 2 second mark never happened before.
     
    Last edited: Aug 21, 2009
  4. dave

    Dave New Member

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  5. unclejed613

    unclejed613 Well-Known Member

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    it could be the antenna probe on the magnetron. if they get enough buildup of grease or whatever on them, they arc over. one word of caution. the power supply cap for the magnetron holds quite a charge (about 5000V), so make sure you discharge the cap before turning any screws inside the cover. make sure you have the unit unplugged before opening it. there are usually cover switches that disconnect the power when you open the cover, but if the oven is more than a few years old, those switches may stick.. once you've taken care of the obvious safety stuff, inspect all of the high voltage wiring for signs of arcing (burn marks on the wires or chassis). if you still don't see anything there, remove the magnetron from it's waveguide box, and look for signs of arcing inside the waveguide box and on the antenna probe of the magnetron if there are signs of arcing (burn marks, pitting of the antenna probe) replace the magnetron and clean the waveguide box and it's mica window. if the mica window has tracks burned into it replace it too.
     
  6. ParkingLotLust

    ParkingLotLust Member

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    Thanks for the tips, Ill tear it down tomorrow and see whats going on inside. Odds are, if something is damaged, I/we will most likely just replace the microwave, as it is nearly 12 years old anyways (I originally thought it was replaced during the time we lived in this house, but apparently it is the original one that was purchased when the house was built!)
     
  7. ParkingLotLust

    ParkingLotLust Member

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    There are no arc marks that I saw, but the noise is definately more prominant with the case off. Attached is another clip of the sound; this time you can hear it a lot better. With the case off, the noise seems to be coming from here:
    [​IMG]

    Specifically, this unit (which appears to be the magnetron):
    [​IMG]

    Ideas? How safe is it to unhook and remove the magnetron? Ive never delt with anything that had to do with microwaves before. Is this noise normal for a ~12 year old microwave or is it about time to get another? The microwave seems to work just fine, other than the noise.
     

    Attached Files:

    Last edited: Aug 26, 2009
  8. unclejed613

    unclejed613 Well-Known Member

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    yes that's the magnetron, and the box it's sitting on is the waveguide cavity. what's that black spot at the lower left corner of the cavity on the white plastic cavity support? (just to the right of the screw). another test for arcing would be to run the oven with the room lights off and if you see a blue or yellow (blue from just arcing, yellow if some organic material like grease or plastic is involved in the process) glow or flashes from inside the cavity or inside the cooling vent in the magnetron.. another possibility for a noise source is a loose screw being vibrated magnetically or if the glue holding the magnets in place around the magnetron has broken loose, the magnets are vibrating along with the 60hz current pulses through the tube. this wouldn't pose much of a problem unless the magnets get so loose, they vibrate out of position enough to reduce the efficiency of the magnetron (rare).


    edit.....
    listening to that clip again almost sounds like the relay that applies power to the transformer (which i'm guessing is the one to the right top of the magnetron in the first picture) is having a hard time pulling in, and buzzes a bit when it pulls in. if so that particular buzzing sound can be fixed easily.... replace the filter caps in the low voltage power supply.

    try this. take the cardboard tube from a roll of paper towels and use it like a stethoscope to localize that noise a bit more (don't use a toilet paper roll, they're too short, especially with 5kv running around loose)
     
    Last edited: Aug 26, 2009
  9. user_88

    user_88 Member

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  10. killivolt

    killivolt Well-Known Member

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    This is the secondary portion if you get any idea's about tearing it apart for any reason.

    Beryllium oxide (BeO) is a white crystalline oxide. It is notable as it is an electrical insulator with a thermal conductivity higher than any other non-metal except diamond, and actually exceeds that of some metals.

    This is in and around the inside of the magnetron and will be very dangerous if handled. Stay away from it one accidental exposure could result in an incurable disease.

    kv

    P.S. look for some arcing in and around the wave guide plate inside the microwave sometimes you can get grease build up and it will arc thru on the sharp corners of the opening exposing the paint.

    Look for a fiber plate covering a square hole in the top of the microwave inside.
     
  11. unclejed613

    unclejed613 Well-Known Member

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    i don't know for sure whether this is an industry standard of some kind, but every time i've seen a sample of BeO as part of a tube, transistor or even a heatsink insulator, it's been a pink or purple tinted ceramic.
     
    Last edited: Aug 29, 2009
  12. killivolt

    killivolt Well-Known Member

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  13. ParkingLotLust

    ParkingLotLust Member

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    I tried it again with the top off and the sound is definately coming from the magnetron. I showed this to my parents and they opted to just buy a new magnetron, as theyre quite cheap. When the new one arrives, Ill have a look down the cavity (Im just afraid of breaking something and leaving them without a microwave for awhile).
     
  14. ParkingLotLust

    ParkingLotLust Member

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    Well, I received the "replacement" magnetron almosdt a week ago, and while it was the same model number, the piece sticking out the bottom was too long, and didnt fit in the waveguide box. After emailing the company, they issued a full refund, but unfortunately that was the only one they had. I tried emailing the person who is listing the other one on eBay to try to get a measurement of the "piece" so I dont have to go through the same thing again, but it has been days and they havent answered. My parents have decided to just replace the microwave, so if anyone would like any HV parts from a microwave which is in otherwise perfect condition, let me know!
     
  15. unclejed613

    unclejed613 Well-Known Member

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  16. ParkingLotLust

    ParkingLotLust Member

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    I just checked the site, and apparently the model I need is discontinued. There are a few models listed, and the full model number on my magnetron is 2M261-M32 G24-04260. It seems that the G's are hard to find, as there are other models with a different suffix on eBay, but no G's. Ahwell, time for a new µwave!
     
    Last edited: Sep 22, 2009
  17. HiTech

    HiTech Well-Known Member

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    The best and safest solution in the end was to replace the entire oven, that is since your folks apparently decided tnot to take it to a professional serviceman. These appliances are absolutely nothing to experiment with by those who are not in the know or mildly knowledgable about them. I'm glad to see you opted out of repairing it and I'm sure they probably weren't aware of the very dangers that you were flirting with. Throw the darn thing out... they are common on trash night for the rest of us here that may need a part or two, let alone the parts from your problem unit. Screw the covers back on the oven to protect the trash man or passerbys. You never know if that cap is charged or not.
     
  18. ParkingLotLust

    ParkingLotLust Member

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    Yeah, if it was anything more than just screwing in a new magnetron, I was going to toss it anyways - the danger the HV psu poses isnt worth the cost of a $200 microwave.
     
  19. HiTech

    HiTech Well-Known Member

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    But, replacing the magnetron certainly involves exposing yourself to the HV supply. Once you remove a microwave oven's cover, you are immediately at risk... and any srevicer should always keep that notion at the front of their mind when they pick up a screwdriver! Now, I really question how realistic your safety-mindedness is?:confused:
     
  20. ParkingLotLust

    ParkingLotLust Member

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    Exposing as in being near it doesnt bother me that much. The HV supply is at the bottom of the microwave, the magnetron is at the top. By exposing myself to the HV supply I mean trying to disconnect and remove the supply, and trying to change parts on it. I have no problem being near something dangerous, as long as I feel safe working on it, but I draw the line at touching it or trying to remove it.
     
    Last edited: Sep 29, 2009
  21. unclejed613

    unclejed613 Well-Known Member

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    you could use it to make a dust precipitator for an air filtration system........ or use a black light bulb and some chicken wire to make a monster bug zapper......... if it were an FBT type supply like those used in panasonic ovens, i could think of a few other uses (not driving a CRT.... wrong polarity)
     

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