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Old 06-27-2022, 08:43 AM   #1
Nevillet
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Default 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 at 09:31 AM..
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Old 06-27-2022, 04:53 PM   #2
sam_sam_sam
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Default Re: Microwave advise please

Quote:
Originally Posted by Nevillet View Post
Hi My gut feeling is that the magnetron is suspect but Id 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
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Old 06-27-2022, 05:56 PM   #3
redwire
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Default 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.
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Old 06-28-2022, 05:40 AM   #4
Nevillet
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Default 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
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Old 06-28-2022, 10:19 AM   #5
sam_sam_sam
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Default 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 at 10:28 AM..
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Old 07-14-2022, 10:31 AM   #6
Nevillet
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Default Re: Microwave advise please

I replaced the magnetron and it cured the problem.

Many thanks to all.
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Old 07-14-2022, 02:39 PM   #7
redwire
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Default 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?
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Old 07-14-2022, 02:47 PM   #8
Nevillet
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Default 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.
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