Repair and disassembly guides for GE Microwave ovens.

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Magnetron or Diode or both?

Hey folks, I have a GE Profile microwave and it started arcing. I took it apart and pulled the magnatron. It was arcing between the top of the magnatron tube and the shielding on the microwave. I tested the diode and it is bad for sure. My main question is did the magnatron possibly go bad and arc causing the diode to blow, or would the diode going bad cause the magnatron to arc. I suppose my question boils down to do I just replace the diode or are both parts bad. Oh and I tested the resistance on the Magnatron, the schematic calls for .5ohm and it measure .6-.7

Any help is appreciated.

Thanks,

Brett

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With 240V device i would suggest against replacing parts on things that have failed in this manner, it could be life or death.

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I totally agree on this call.

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Good morning Edwin Lebish! The HV capacitor holds 4000-6000 volts, even uplugged. Don't attempt to check voltage on the HV circuit. It's much safer to check the amperage with a line splitter. This amperage test is quick, easy, accurate and safe.

Place a cup of water in the microwave. Attach your amp probe to the line splitter, plug in and run microwave 10-20 seconds.

10-14amps = all is good

3-9 amps = transformer is good. Problem is in HV circuit. The magnetron is more likely to fail than the capacitor.

Under 3 amps the problem is in the LV circuit. There is only 1 diode in a microwave. It's inexpensive and simple to replace. To test the diode, I use a 9 volt diode tester. Honestly, if I'm replacing any part in the HV circuit I replace the diode too.

ALWAYS DISCHARGE THE CAPACITOR BEFORE DOING ANY REPAIRS

Unplug the microwave and once you remove the outer cabinet discharge the capacitor before doing anything else!

Be safe. The capacitor will kill and has killed many technicians.

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Doubtful that people have died from the capacitor discharge, if the item was not operating. It is high voltage but not much current flows during a discharge. It's similar to the 30 kv discharge of a spark plug wire on a car or the old TV HV wire on the picture tubes(40kv), it has a heck of a kick but is not lethal, unless you are holding it while the appliance is operating. I've experienced both, and don't recommend it.

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I disagree. The stored energy in a capacitor varies as the square of its terminal voltage, and the number of coulombs stored -- these are the things that do the work -- varies directly as the terminal voltage. Clearly, high-voltage capacitors are to be respected. I've been very sorry to pick up a capacitor charged to about 200 volts, never mind 2,000 volts! Discharge them before working around them!

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Peter - you are a very wise and smart man! Thank you!

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Unplugged, the HV capacitor holds 4K-6k volts and has killed many people. Don't attempt to discharge the capacitor or do any repairs if your not certified.

I always replace the diode with the magnitron. Just like I would a belt and pulley on a dryer.

Sparks can be caused by several issues; a bad wave guide, grease build up and more.

The first test I do on every microwave is how many amps it is pulling.

10-14 amps -all components are good.

3-9 amps-transformer is good-problem is in HV circuit

Less than 3 amps problem is in LV circuit

Always test with a glass of water. Finish repairs with a survey test

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LadyTech where do you check for the amp draw? Main power cable?

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Yes. I use a line splitter. The power cord plugs into the splitter and the splitter plugs into the outlet. The splitter has a place to clamp your amp meter.

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Excellent. Thanks.

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[edit: clarification] Your suspicion is correct, that one component going bad can lead to another failure. But your measurement of the magnatron suggests it's sound -- it depends upon the design spec variance allowed in the resistance measurement.

I would try the diode, and power up the microwave with all covers in place. As others have mentioned, these appliances have very high voltage components and you can get hurt trying a DIY repair. Ensure all capacitors are discharged, you have no jewelry on, etc. If you're new to this, leave it to a professional -- the cost of a replacement is far more economical than the potential injury you can incur.

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I always unplug get it first then disconnect primary coil of Transformer then I discharge the capacitor. Any parking would be indicative of the need to replace wave guide hey you need to check the stirer motor if it has one

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What is the value of the high voltage from the transformer going into the magnetron so I can measure it with my HV meter? Oven wattage is 1100. Also, what method can I use to test the HV diode since most meters that have a diode test function can not test such diodes? I assume a HV diode is a diode that actually is several diodes in series in one unit and the average meter does not supply enough voltage to forward bias the diode?

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Edwin Lebish - Please don't try to check the voltage on the high side. There is no need to. All test can be done safely by checking amps or resistance.

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Edwin,

The only difference between this microwave diode and other diodes is the voltage it is rated at. This diode is rated for thousands of volts, which is what the magnetron circuitry produces. It is not many diodes in series, as you suggest. Testing the diode is done just like any lower voltage diode, infinite resistance in one direction, low resistance when you reverse the ohmmeter test leads (less than 10 ohms).

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Important, your Multimeter on the diode test setting must have a battery voltage of 6v or higher else you will have an infinity reading and think that the Diode is faulty.

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Brett Houts will be eternally grateful.
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