Tip & How-To about Microwave Ovens

How to replace a microwave oven's diode:

Replacing a high voltage diode

The first thing you must do to replace your microwave's diode is unplug the unit from the wall outlet.

Next you will have to discharge the high voltage capacitor. A capacitor stores large amounts of electricity even when the unit is unplugged. It is necessary to discharge the high voltage capacitor in order to avoid receiving an electrical shock.

Diode replacement is relatively straightforward because most high voltage diodes have a press fit, also known as Fast-On, or they have ring lugs. If your replacement diode can be installed either way, make sure you get the right polarity. Remember that a diode will conduct an electrical current when a forward voltage is applied, but when a reverse voltage is applied, there is no conduction.

Remove the diode from your microwave and replace it with the new one. You may be able to crimp the new diode onto the wire leads, without welding or soldering them together. If you do crimp the diode onto the leads, be sure not to apply too much pressure, as this may cause connection problems either now or in the future.

I hope this is helpful.

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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

unit completely dead. no lights no fan no keypad wall outlet tests OK


The microwave oven internal fuse has blown, unplug unit, remove top case 2 to 6 screws, on right side look for a long rectangular silver capacitor, "carefull high voltage" the ceramic fuse should be next to it, "white body with silver ends" remove and replace with same rating. If the fuse blows again chances are the door switch is defective and must be replaced.

Jun 18, 2011 | Microwave Ovens

1 Answer

first the microwave clock etc worked but the fan and table and microwave didn't work now nothing works anymore i checked the fuses they are ok the doorswitches work also ok. what is the next step to do


Probably the failure of a high-amperage fuse inside the unit. The electronics are generally separately fused so one section can fail leaving the other functioning.
If there is no external fuseholder on the back panel, it will be necessary to remove the housing to access the innards.
The fuse that has blown may have blown because of metal fatigue but the cause could also be more serious, namely the high voltage diode (or diode bridge) that converts high voltage AC into the DC required for the magnetron or even the magnetron itself may have developed an internal short.
If you locate the fuse, buy two of them and if the first replacement fails again, then the diode(s) or magnetron has failed and with the cost of service plus parts markup, you will be better off replacing the whole unit.

Apr 30, 2010 | Sharp R530E 1200 Watts Microwave Oven

1 Answer

My MH1150XMS-4 just stopped working suddenly.


The main fuse or the thermal cutout is probably blown. If the main fuse is blown, most likely the high voltage capacitor is shorted and must be replaced. If this is the case, it's a good idea to also replace the high voltage diode because it took a large over-current hit before the fuse blew. Be sure the oven is unplugged before measuring the resistance of the fuse or capacitor (the diode should read open in both directions because the forward voltage is more than a typical ohmmeter can put out). (Note: replacing the fuse without identifying and fixing the short or overload will simply waste the new fuse. It's not like the old farmhouse with one fuse for a dozen outlets going out because one item too many was plugged in.) The capacitor is available on Amazon for less than $17 (be sure the voltage and uF values match the one in your oven), the diode is about half of that, and the fuse should be under $3.

If the thermal cutout is blown, check the magnetron cooling provisions - make sure the fan turns freely, the blades are clean, and all vents are clean. After replacing the thermal cutout, verify that magnetron cooling fan runs at speed when the oven is running. Keep your hands and tools out of the oven if you are testing it with the cover off. The high voltage side can be energized by as much as 1800 Volts. An arc from this can cause serious damage or personal injury.
Amazon com 0CZZW1H004S Kenmore Microwave Capacitor Drawing Hi Home...

Oct 18, 2017 | Whirlpool MH1150XM Convection/Microwave...

2 Answers

Microwave


Magnatron is suspect. Need to put a voltmeter on the input (primary) side to the high-voltage transformer (big heavy iron thing in there) Should be getting 120Vac when it goes to cook cycle. Don't touch the other (high voltage) side of this transformer. If the power is there, you are looking at replacing the magnatron. Its affordable if you do it yourself - buy the part on EBAY - lookup "universal magnatron"

Jan 02, 2008 | Microwave Ovens

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