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How to test H.V. Capacitor - Microwave Ovens

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You need a high rated ohm meter, with leads on resistance should go way down then come up, reverse leads and same should happen again. cap is either open or not or if a short bad also.

Posted on Nov 06, 2012

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Sanyo EM-SL40S microwave everything seems to be working fine but food doesn't get hot?


see this causes and fix it. GOD BLESS YOU
Power Diode

A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.


High Voltage Capacitor

A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating but you are hearing a buzzing or humming noise. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.


Magnetron

A defective magnetron is the third possible cause of why your microwave is not heating, but you can hear a buzzing noise. Test your microwave's magnetron. Replace it if it is defective.


Thermoprotector If the microwave doesn't heat the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it's blown.

Main Control Board If the microwave doesn't heat the main control board may be defective. This is not common. When a microwave doesn't heat the problem is usually within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.
High Voltage Transformer If the microwave does not heat, the high voltage transformer might be burned out. Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food.
10_2_2012_12_38_27_pm.jpg10_2_2012_12_38_56_pm.gif

Oct 01, 2012 | Microwave Ovens

1 Answer

Don't heat consistantly micro or conv--sympthems-- no oven light no heat --occasionally ok--- ser. #113806


Hello there,

The problem could be from the power diode. A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.
Also a capacitor could be faulty. A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating or working intermittently. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.
Finally, the magnetron could be faulty. A defective magnetron is the third possible cause of why your microwave is not heating. Test your microwave's magnetron. Replace it if it is defective.
You will have to test them and replace the faulty component amongst the three factors.
Hope this helped.
All the best.
Elect_Comp

Oct 31, 2011 | Sharp R-1870 Convection/Microwave Oven

1 Answer

Microwave won't heat, timer goes off after 1 minute or so


Microwaves are a quick, convenient solution to the hassle of preparing and cooking hot dinners. They are popular appliances with students and large families where food often needs to be prepared fast. Microwaves use radio wave technology harnessed through an antenna, known as a "magnetron," to create friction between food or liquid molecules, causing them to heat up. Some microwaves can cease to function properly, resulting in the appliance running but failing to produce any heat.

  1. Magnetron
    • Magnetron tubes are often the source of heating problems in microwaves. Before having any repair work done, check the warranty on your microwave. Many companies offer 10-year warranties on magnetron tubes so you may be able to get it repaired professionally for free. Otherwise, unplug the microwave then remove the rear casing with a screwdriver. Locate the tube inside the microwave and check it for burn marks. A burnt tube cannot usually be repaired and will require replacement. A tube that doesn't appear burnt should be tested by a qualified technician to see if it can be repaired.
    High Voltage Capacitor
    • A microwave capacitor holds electricity as the appliance is running. A malfunctioning capacitor can lead to the microwave not heating, along with an irritating buzzing sound. Test the capacitor by first disconnecting the power then removing the wires attached to the capacitor. A capacitor with burn marks is usually damaged beyond repair and will require replacement. A capacitor can be tested by connecting each of the probes of an ohmmeter to the capacitor terminal. Each probe should provide a reading of infinity if the capacitor is working properly.
    Power Diode
    • The diode in a microwave oven is a one-way pathway that channels electricity from the capacitor. A malfunctioning diode can sometimes be the cause of a microwave that won't heat. The heating problem is often accompanied by a loud buzzing noise. You can test the diode by first unplugging the microwave oven, disconnecting the diode from the capacitor then measuring the level of electricity inside the diode with an ohmmeter. The ohmmeter can determine whether the electricity in the diode is flowing in one direction as it should. In most cases, the magnetron tube will have to replaced as well if the diode is damaged.
    Safety
    • Disconnecting the plug from your microwave to carry out an inspection does not guarantee safety. Even an unplugged microwave still has electricity running through its components, which can lead to severe electric shocks. Unless you have previous experience in dealing with electrical appliances, it is advisable to hire a technician to test component parts rather than undertake the job yourself. Anyone without a basic knowledge of electrical currents and safety should avoid testing components altogether.

Oct 03, 2011 | Microwave Ovens

1 Answer

Is diode on delonghi dmx50 supposed to be OL or a resistance through and if so what would be the resistance


Hi and welcome to FixYa, I am Kelly
First off before testing the diode you must disconnect ONE terminal of the diode to properly test it.
This is going to sound nuts but the answer is it should read both OL and ZERO .... The reading is Open in one direction (OL) and ZERO in the other direction. Just swap the test probe leads on the diode. The purpose of the diode is to only allow the flow of energy on ONE direction. So in one direction it acts like a wire (ZERO ohms) and when you reverse the leads it acts like you cut the wire. (infinity or no resistance) If it reads ZERO in both directions or infinity in both directions it is bad.
Just make sure you have shorted across the HV Capacitor several times by holding a screwdriver well back on the handle before even messing with the diode. After you have made sure that the capacitor is no longer charged... test the capacitor by probing the 2 terminals and watching for a brief jump in resistance and then resistance drifts to infinity. Reverse the test leads and watch for the same jump in resistance and drifting to infinity (OL) No Jump in resistance = Bad Cap Also read each of the 2 terminal posts to the body of the capacitor. NO resistance is allowed. Any resistance reading below 240,000 Ohms when reding either terminal to the body of the capacitor = bad capacitor.

ALL TESTS ARE DOWN WITH NO POWER TO THE UNIT! (Unplugged)

Thanks for choosing FixYa,
Kelly

Apr 16, 2011 | DeLonghi MW 535 Microwave Oven

1 Answer

Food won't cook or heat up - everything else works


HI:
The problem is a open high voltage diode on the high voltage capacitor, this link will help you in repairing or testing the diode yourself, CAUTION!! The high voltage capacitor must be discharged before attempting any repairs or testing, discharge by shorting the posisitive terminal to ground. the diode is attached to one of the terminals of the capacitor and the other end to ground.
http://www.partselect.com/microwave+test-diode+repair.htm

Feb 05, 2011 | Microwave Ovens

1 Answer

Microwave won't heat, light ,clock works the microwave just won't heat the items in it.


hELLO THERE
when a microwave quits heating but every thing else is ok normally
investigate these 4 areas

Investigate these three areas if your microwave won't heat but you hear a loud buzzing or humming noise:
microwave_diode.jpg Power Diode

A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.

picturena.gif High Voltage Capacitor

A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating but you are hearing a buzzing or humming noise. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.

microwave_magnetron.jpg Magnetron

A defective magnetron is the third possible cause of why your microwave is not heating, but you can hear a buzzing noise. Test your microwave's magnetron. Replace it if it is defective.

Nov 09, 2010 | GE Spacemaker JVM1640SJ Microwave Oven

1 Answer

I have a Samsung microwave model SMH7177STE/BE. Will only heat a few minutes before and shut off, now there is no heat. I am a licensed elect. but no experience with microwaves and having difficulty...


Its tripping a high limit most likely. Be careful there is 2100 to 4000 volt high side with a capacitor if its not an inverter. The standard components consist of noise board, fuse, touch panel and power controller, high limits, door switches, whipper motor, fan, transformer, capacitor, transformer, magnetron, diode, plate rotator.
Discharge cap (for safety and further testing).. Test fuse; if fuse tests blown test door switches first. Test limits. Check amp draw with slow blow fuse; open door to stop unit and again discharge capacitor. Test resistance to ground on whipper, fan, magnetron, light. Test resistance lead to lead (measurable on motors/coils/magnetron). Test capacitor in ferrads, compare to spec on print. Check diode forward and reverse. Test output voltage from power control board to transformer. Test transformer coils.
Best of luck and play safe; dont test voltage output from the transformer, voltage at capacitor or magnetron.

Aug 03, 2010 | Samsung Microwave Ovens

1 Answer

No power. I changed fuse but microwave blows it immediately.


Be very careful! Standard microwaves have 2100volt capacitors and commercial ones 4000 volt capacitors.
*Decharge your capacitor(s) before doing diagnostics*.
You are now testing the high voltage side (as it works on convection). The main components are a transformer, a capacitor, a diode and a magnetron (havent seen a triac in a panasonic residential). If you have a proper meter that can test uf, decharge the capacitor, then test the capacitor, if it reads 0, you need a new capacitor (10$ used typically, 14$ new from ebay). To test the magnetron, decharge the capacitor first, remove the spade connections, test each leg to the frame of the microwave... if it shows measurable resistance, the magnetron is bad. The transformer is not something you test as I personally dont have a 4000 volt meter. If the diode, the magnetron and capacitor are okay, then the transformer is bad. To eliminate any other function, disconnect the low voltage to the transformer run a micropower cycle and check the fuse.
Hope that helps. My first instinct is the capacitor.

Nov 14, 2009 | Panasonic NN-T888S Convection/Microwave...

1 Answer

We had a small fire caused by a metal sticker inside our microwave. Now the unit is heating items, but not as much as it should. Can this be fixed or do we need a new microwave?


Use extreme caution when working on microwave ovens. Even when unplugged, the high voltage capacitor can store up to 2,000 volts! discharge the capacitor before doing anything else inside the box.
This may be a bad magnetron. Ohm test between the magnetron terminals, should be less than 3 ohms. Test from magnetron terminal to ground, should be open.

* Defective HV capacitor. Test with capacitor meter or ohm meter.

* Defective control board. Test for power going to board. If exists, problem lies on board somewhere.

* HV Rectifier is shorted or open. Test forward and reverse bias with a megohmmeter. If continuity in both directions, rectifier is shorted, replace. If no continuity in either direction, rectifier is open, replace.

In general because of safety issues (very high voltage, even when unplugged), I would suggest you get a new one.
Good luck.


Aug 14, 2009 | Kenmore Microwave Ovens

2 Answers

Microwave doesn't heat up


There are three solutions (source) =>

http://www.partselect.com/repair.aspx?appliance=microwave&part=no-heat

Power Diode

A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.

High Voltage Capacitor

A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating but you are hearing a buzzing or humming noise. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.

Magnetron





A defective magnetron is the third possible cause of why your microwave is not heating, but you can hear a buzzing noise. Test your microwave's magnetron. Replace it if it is defective.

Dec 31, 2008 | Microwave Ovens

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