Question about Microwave Ovens

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Microwave oven high voltage capacitor has zero resistance between terminals, and no continuity between terminals and the capacitor's case.

Lights, turntable, fan, display work. Door switches O.K. High voltage capacitor's leads disconnected for testing. When I checked the discharged high voltage capacitor, I found that there was zero resistance between the terminals (the meter pegged, and stayed pegged). Same result when ohmmeter leads were reversed at the capacitor terminals. There was infinite resistance between either of the capacitor's terminals and the capacitor's can using a digital ohmmeter. Same results as above using an analog ohmmeter. Do those readings definitely indicate a bad capacitor? Are there other tests? I have only VOM's.

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  • Norman Jan 18, 2013

    (The Microwave oven stopped cooking)

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Posted on Jan 02, 2017

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MicrowaveSvc
  • 9085 Answers

SOURCE: Oven won't heat even though each component seems to be functional.

Even though the magnetron passed the continuity tests, it can still be bad. In fact, most of them fail in ways that do not show up in continuity tests.

And I am 99% certain yours is bad, especially since you have proven that the filament voltage and high voltage DC is being produced and sent to the magnetron.

I must say that the testing you have done is not recommended for people without plenty of experience, but apparently you did it safely. Please don't press your luck, since the high voltage can be instantly lethal.

For Goldstar / LG / L.G. parts, call 1-800-243-0000 (M-F, 7am-8pm CT, Sat 8-5 CT) and choose the appropriate prompt from the menu or visit here.

We're happy to help and we appreciate your thoughtful rating of our answer.

Posted on Jul 18, 2008

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  • 561 Answers

SOURCE: microwave does not work unti, door slightly

this may not be the switch its self but its physical position in relation to the door acuator. either the switch needs adjustment or the door actuator or door itself. recommend certifed engineer advise on this problem.

warning: mircowave is a high energy, if doors are not seated correcly then energy may leak past door shielding and cause injury.

Posted on Nov 13, 2009

heatman101
  • 43501 Answers

SOURCE: Everything seems to work except

Hi,


Here is a tip that will help you to figure out what is wrong with your Microwave Oven....

Microwave Oven Basic Troubleshooting Tips

heatman101



;



;

Posted on May 03, 2011

SOURCE: GE Profile JE2160 - Just stopped working. Touch

Hi there,

Microwave ovens use a series of micro switches to operate as interlocks to ensure the unit will only operate once the door is securely closed.

If these locks are not operating properly, the timer would count down just like it was operating. There will be no noise like the normal vibration or fan sounds when the start button was pressed. It will simply act like it will operate, but it will never turn on any of the components.

You would need to check these switches if they are functioning properly and would need the help of a qualified technician to test them. If you plan to do it yourself, Check if the switches are mechanically operating and that electrical continuity would change as it was actuated.

There will be at least three of these switches aligned so they close in a specific sequence when the oven door is closed.

This closure process is designed to prevent someone from just sticking something in to actuate the switch and run the microwave with the door wide open and becoming exposed to the microwave energy.

Two of the switches are in place to provide power to the units high voltage section and to tell the control board when the door has been closed. These are usually normally open switches.

The third switch is called the monitor and acts as a safety switch blowing the internal appliance fuse in the event any tampering is going on, and this one is usually a normally closed switch.

If you find the fuse inside your microwave is now an open circuit, check the monitor switch as it may be the cause.

Hope this helps.

Posted on Aug 19, 2011

  • 45646 Answers

SOURCE: Blown fuses

Well you certainly have done a lot of work on a microwave that is not worth the effort. When fuses blow and destroy other items ,it is time to junk it and up date. I have found that when something like what happens 9 times out of 10 it will be the magnetron or transformer either of which will be more than 1/2 the cost of a new machine.

Posted on May 18, 2013

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How to troubleshoot a Magichef md# MCD1611ST microwave that is not heating anything at all.


Most Frequent Causes for Microwave not working Thermal Fuse

The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. The thermal fuse cannot be reset-if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. The thermal fuse cannot be reset-if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse

Sep 28, 2016 | In Microwave Ovens

1 Answer

Magnetron shows no resistance between terminals is it bad


The resistance between the terminals should be low, but not zero. These are the terminals that feed the heater/cathode. It draws a fairly significant current at a low voltage. To heat up, it must have some resistance.

There should not be any continuity between either of these terminals and the case.

Jul 01, 2014 | GE Spacemaker JVM1640SJ Microwave Oven

2 Answers

Blown fuses


Well you certainly have done a lot of work on a microwave that is not worth the effort. When fuses blow and destroy other items ,it is time to junk it and up date. I have found that when something like what happens 9 times out of 10 it will be the magnetron or transformer either of which will be more than 1/2 the cost of a new machine.

May 18, 2013 | Microwave Ovens

1 Answer

Sharp convection microwave oven model R1875F. It's cooking on the left side faster then the rest of the oven. It seems to burn on the left side and not cook in the middle.


see the next causes. God bless you
Diode The high voltage diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron which emits the energy that cooks the food. If the diode burns out, a lower A/C voltage reaches the magnetron, which is not sufficient to power the magnetron. When the diode fails it is often visibly burned out. If it appears to be good, it can be tested with a volt-Ohm meter capable of testing diodes. High voltage diodes frequently fail and are one of the most common points of failure in a microwave oven.

Door Switch If the microwave does not heat, one of the door switches might be defective. Microwave ovens normally have three door switches, if any of them fail the microwave does not turn on and does not heat. Check the switches for continuity with an Ohm meter.

Magnetron If the microwave oven doesn't heat the magnetron tube might have burned out. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the microwave oven is turned on when it is empty this can cause the magnetron to burn out. Once it is burned out it has to be replaced, it's not repairable.

High Voltage Capacitor If the microwave doesn't heat the high voltage capacitor might be defective. The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out the entire high voltage circuit stops working properly. The high voltage capacitor can be checked with a special VOM meter which has a capacitance testing capability. Be aware that the high voltage capacitor can retain a charge of more than 3,000 volts and can injure or kill a person if not handled properly. Only trained technicians should perform this type of testing.

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.

Thermal Fuse If the microwave doesn't heat the thermal fuse may have blown. It can be tested for continuity. Watch our fuse testing video for more information.

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.
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Oct 03, 2012 | Sharp R-1870 Convection/Microwave Oven

1 Answer

Maytag microwave problem everything seemingly works but does not heat. Help


see this causes and fix it. God bless you
Diode The high voltage diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron which emits the energy that cooks the food. If the diode burns out, a lower A/C voltage reaches the magnetron, which is not sufficient to power the magnetron. When the diode fails it is often visibly burned out. If it appears to be good, it can be tested with a volt-Ohm meter capable of testing diodes. High voltage diodes frequently fail and are one of the most common points of failure in a microwave oven.

Door Switch If the microwave does not heat, one of the door switches might be defective. Microwave ovens normally have three door switches, if any of them fail the microwave does not turn on and does not heat. Check the switches for continuity with an Ohm meter.

Magnetron If the microwave oven doesn't heat the magnetron tube might have burned out. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the microwave oven is turned on when it is empty this can cause the magnetron to burn out. Once it is burned out it has to be replaced, it's not repairable.

High Voltage Capacitor If the microwave doesn't heat the high voltage capacitor might be defective. The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out the entire high voltage circuit stops working properly. The high voltage capacitor can be checked with a special VOM meter which has a capacitance testing capability. Be aware that the high voltage capacitor can retain a charge of more than 3,000 volts and can injure or kill a person if not handled properly. Only trained technicians should perform this type of testing.

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.

Thermal Fuse If the microwave doesn't heat the thermal fuse may have blown. It can be tested for continuity. Watch our fuse testing video for more information.
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.


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Oct 01, 2012 | Maytag MMV4205 Microwave Oven

1 Answer

GE Dual Wave 11 Microwave over Oven. The


Hello there,

When your microwave is acting in this manner, there seem to be a problem somewhere inside the unit. The problem most likely is as a result of a faulty magnetron or a faulty power diode or the high voltage capacitor.

A diode is an electronic component that readily passescurrent in one direction only and blocks the flow of current in the opposingdirection. If your microwave's diode has become defective, your microwave willnot heat and you will hear a buzzing noise. Test the diode to determine if thisis the cause of your problem. Replace it if it is defective.Testing a diode NOTE: Before you test your diode, make sure your microwave isunplugged, and that you discharge themicrowave's capacitor.Whetherit is shorted or open, a defective diode will most likely show some sign ofdefect. Defective diodes will usually emit an electrical burning smell,signifying its defectiveness. Also, it may have split in two, or it may exhibita burned crack, or possibly even a blistered spot. Ashorted diode is indicated by a loud humming noise from the high voltagetransformer, and no heat produced when a cook cycle is initiated. Whereaslittle or no heat produced in your microwave, with an absence of a hummingnoise is indicative of an open diode. In either case, the diode has to bereplaced. Withyour microwave unplugged, and your capacitor discharged, use extreme caution toremove the lead that leads to the capacitor. You can leave the groundconnection attached. The side of the diode that goes to the ground is usuallymarked with a dot, stripe, or arrow. Set your ohmmeter to R x 10,000 or higher.Touch the positive meter probe to the anode and the negative meter probe to thecathode to measure the resistance across the diode terminals. Remember that thecathode is on the side that goes to the ground, which is often marked by a dot,stripe, or an arrow. Anormal diode, that is a non-defective diode, will read anywhere from 50,000 to200,000 ohms. Differences in microwave make and model account for this largerange in resistance readings. Reversethe meter probes and measure resistance while touching the positive probe tothe cathode and the negative probe to the anode. Reversing the probes like thisshould result in a reading of infinity. Unless a bleeder resistor is present.The presence of a bleeder resistor would produce a reading of the value of theresistor. Replacing a high voltage diode Thefirst thing you must do to replace your microwave's diode is unplug the unitfrom the wall outlet. Nextyou will have to discharge the high voltage capacitor. A capacitor stores largeamounts of electricity even when the unit is unplugged. It is necessary to discharge the highvoltage capacitor in order to avoid receiving an electrical shock.Diodereplacement is relatively straightforward because most high voltage diodes havea press fit, also known as Fast-On, or they have ring lugs. If your replacementdiode can be installed either way, make sure you get the right polarity.Remember that a diode will conduct an electrical current when a forward voltageis applied, but when a reverse voltage is applied, there is no conduction.Removethe diode from your microwave and replace it with the new one. You may be ableto crimp the new diode onto the wire leads, without welding or soldering themtogether. If you do crimp the diode onto the leads, be sure not to apply toomuch pressure, as this may cause connection problems either now or in thefuture. A capacitor is an electrical device which storeselectricity. A defective capacitor may be why your microwave is not heating butyou are hearing a buzzing or humming noise. The capacitor will have to betested to determine if this is the cause of your problem. A defective capacitorwill have to be replaced before your microwave will work again. Make sure you discharge thecapacitor before you test it, though.Testing a capacitor NOTE: Before you test this component, make sure your microwave isunplugged, and that you have discharged thecapacitor.Beforeyou begin this test, first examine the state of your capacitor. Does it appearto be burned in any way? Is there an oily film present on the component? Withyour microwave's cabinet opened up, take careful note of which wires attach tothe terminals of your capacitor. You may want to label them with masking tapeso that you know which wires are to be reconnected where. Also, take note as towhether or not your microwave uses a bleeder resistor. If your model does haveone, you do not need to remove it, but keep in mind that some of your readingswill reflect the meg-ohm resistance of the bleeder resistor.Setyour ohmmeter to the highest resistance scale. Then place each of the meter'sprobes to one terminal. You should receive a reading of infinity, or you shouldreceive the value of the resistor. Now you can reverse the probes so that theyare each touching the other terminal. This should result in the metermomentarily leaning toward the zero mark, but then drifting back to infinity.Reverse the meter's probes yet again. The same pattern should occur again. Nowtouch one meter probe to a capacitor terminal, and the other probe to thecapacitor's metal casing. You should receive a reading of infinity. Now touchthe same meter probe to the other terminal, while keeping the other probetouching the metal casing. Again, you should receive a reading of infinity.However, if an internal diode is present, then the reading you receive could bereflective of the diode's forward bias resistance. You might want to take alook at our diode testing page. Ifyour test does not produce these results, or if your initial visual inspectionof the capacitor reveals signs of damage, replace your capacitor. High voltage capacitor replacement Acapacitor stores large amounts of electricity even when your microwave isunplugged. Have a certified and experienced appliance repair technician examineand replace your high voltage capacitor. This task is much too dangerous forthe average layman to perform on his own. Testing a megnetron NOTE: Before you test this component, make sure your microwave isunplugged, and that you have discharged thecapacitor.Thereare two tests to conduct in order to determine whether or not a magnetron hasbecome defective. If you receive results other than what are detailed below,you will have to replace your microwave's magnetron. Each test is described foryou here: TEST1: Locate your magnetron and labeleach of the wires attached to it so that you know which wires are to bereplaced where. Set your ohmmeter to the lowest resistance scale. Take aresistance measurement between each of the magnetron's terminals by touchingeach probe to one terminal each. Reverse the probes and take a secondresistance measurement. Each measurement should read less than one ohm. TEST2: Set your ohmmeter to its highestresistance scale. Touch one of the meter's probes to a magnetron terminal.Touch the other probe to the metal magnetron housing. Take special caution tonot touch the two probes together. This could result in an inaccurate reading.This test should produce a reading of infinity - indicating an open circuit. Have a certified and experienced appliance repair technicianexamine and replace your magnetron. This task is much too dangerous for theaverage layman to perform on his own

Oct 11, 2011 | Microwave Ovens

1 Answer

I have a Natioanl NN-6207 Microwave,I have replaced the magnetron and the fuse, every time I switch the microwave on it makes a loud humming noise and blows the fuse. The magnetron has two terminals F and...


F and Fa could be the problem but.... You must check the power diode and the high voltage capacitor. One of these is most likely the reason the fuse failed in the first place. Ground the HV capacitor by holding an insulated screwdriver well back on the handle. The locate the Power Diode that will have at least ONE terminal that connects to the capacitor. Power doides are either 3'8 inch wide and 2 inches long or round an liik like a bit resistor with no color markings. ' Check the HV capacitor by rading each terminal to the case of the capacitor (no shorts allowed)
Then read across the capacitor terminals with the meter set on R x 10K. Watch for an initital jump in resistance and then it drifts up to infinity. Reverse test lead positions and you must get the same result. Resistance and then drift to infinity. Any other reading.... infinity in both directions, short to the case or short across the 2 terminals = bad Cap.
If after you perform the above tests and you still have the problem ... knowing you might pop another fuse there are 3 door switches. 2 of them will read resistance / continuity across the terminals when the door is close and one of them will read continuity across the terminals when the door is open. One of the 3 switches has 3 wires on it... the 3rd wire shorts the magnetron power when the door is open and the power relay / HV circuit is powered. This is a built in blow the fuse to prevent magnetron operation with the door open.

I think your are going to find that either the power diode or the HV Capacitor has failed.

Thanks for choosing FixYa,
Kelly

Apr 16, 2011 | GE Microwave Ovens

1 Answer

HV Transformer and Maganatron


I would not recommend an inexperienced measuring secondary voltage on the high voltage transformer! The filament winding produces about 3VAC but the high voltage winding produces well over 2000VAC! And that can be instantly lethal!

I would only recommend measuring the resistance (in ohms) of the windings with power off and capacitor discharged.

We have the full service manual for this model and have uploaded it to our site here to help you.

You will need the free Acrobat Reader to view or print it.

The part number listed by the distributor for the high voltage transformer is RTRN-A527WRE0 (zero on the end, not "oh") which is the same number shown in the service manual.

The two continuity checks on a magnetron are across the filament terminals, which should read about zero ohms, and from each terminal to the case, which should read open or infinity.

Even if a magnetron passes these continuity tests, it can still be bad.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

Oct 04, 2008 | Sharp R-930AK Convection/Microwave Oven

1 Answer

Oven won't heat even though each component seems to be functional.


Even though the magnetron passed the continuity tests, it can still be bad. In fact, most of them fail in ways that do not show up in continuity tests.

And I am 99% certain yours is bad, especially since you have proven that the filament voltage and high voltage DC is being produced and sent to the magnetron.

I must say that the testing you have done is not recommended for people without plenty of experience, but apparently you did it safely. Please don't press your luck, since the high voltage can be instantly lethal.

For Goldstar / LG / L.G. parts, call 1-800-243-0000 (M-F, 7am-8pm CT, Sat 8-5 CT) and choose the appropriate prompt from the menu or visit here.

We're happy to help and we appreciate your thoughtful rating of our answer.

Jul 17, 2008 | LG LRM1250 Microwave Oven

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