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    Microwave advise please

    Hi All,

    I am trying to diagnose a faulty microwave oven and have checked the following components.

    Transformer – The primary and secondary windings have low resistances and no shorts to earth or between pri/sec.

    The high voltage capacitor (1.05uF/2200V) measures fine with no shorts to earth.

    The diode is not shorted or open circuit and when connected to a 9V battery drops 4V.

    The magnetron has a low resistance across the terminals and has no resistance to earth.

    I’ve put a clamp meter around one of the primary lines to the transformer and measured about 4A (240V) when the microwave is ‘on’.

    A cup of water in the microwave does not heat in any way.

    My gut feeling is that the magnetron is suspect but I’d appreciate any opinions on this.

    Many thanks.
    Last edited by Nevillet; 06-27-2022, 09:31 AM.

    #2
    Re: Microwave advise please

    Originally posted by Nevillet View Post
    Hi My gut feeling is that the magnetron is suspect but I'd appreciate any opinions on this.

    Many thanks.
    You are probably correct in your determination of what the issue is

    Depending on the model of your microwave would determine weather or not replacing the
    9 PC LCD Monitor
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    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
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    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

    Comment


      #3
      Re: Microwave advise please

      Last to check is for open filament wiring at the connector/feed-through capacitors or for a bad connection there, or inside the can at the EMI chokes. Magnetron filament is low voltage, high current around 3.3VAC 11A for 36W, but caution it's at the (-ve) high voltage potential and not something to measure safely.
      http://www.hokuto.co.jp/eng/products/magnetron/list.htm

      Measuring mains 4A is a bit misleading becuase there is the transformer's magnetizing current and the power factor needs to be taken into account. So it's not really 4A used, if you have a power meter check how many W it's using.

      Comment


        #4
        Re: Microwave advise please

        The magnetron is a Toshiba 2M303H(EX) and I can't find a replacement in the UK.

        How generic are magnetrons?

        The one I need is in this article:
        http://www.hokuto.co.jp/eng/products/magnetron/list.htm

        Comment


          #5
          Re: Microwave advise please

          Are you able to find the specifications for the one you have and match it up as close to what you have now

          This aspect is going to very important as well to the one you have “ Type of Outline—> Direction of air flow and mounting patterns ”

          Which there several different air flow patterns and different mounting variations so you would have to match this as well
          Last edited by sam_sam_sam; 06-28-2022, 10:28 AM.
          9 PC LCD Monitor
          6 LCD Flat Screen TV
          30 Desk Top Switching Power Supply
          10 Battery Charger Switching Power Supply for Power Tool
          6 18v Lithium Battery Power Boards for Tool Battery Packs
          1 XBox 360 Switching Power Supply and M Board
          25 Servo Drives 220/460 3 Phase
          6 De-soldering Station Switching Power Supply 1 Power Supply
          1 Dell Mother Board
          15 Computer Power Supply
          1 HP Printer Supply & Control Board * lighting finished it *


          These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

          1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
          2 Hem Saw Computer Stack Board

          All of these had CAPs POOF
          All of the mosfet that are taken out by bad caps

          Comment


            #6
            Re: Microwave advise please

            I replaced the magnetron and it cured the problem.

            Many thanks to all.

            Comment


              #7
              Re: Microwave advise please

              That's good you got it fixed. Especially over counter ones are so expensive.
              Where did you buy the replacement magnetron in the UK?

              Comment


                #8
                Re: Microwave advise please

                The microwave was made by Electrolux and the magnetron was supplied by them as a spare item. The price was £70 including delivery.

                Comment

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