Question about Kenmore 62702 Microwave Oven

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Hv transformer how do I test the HV transformer in microwave oven .Need i take it out or just remove connections?.I have discharged cap.Oven runs normall but know heat.This oven seems brand new and never has worked.From a dumpster.

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Check this site under troubleshooting to find more info on how to test those parts.

Posted on Apr 23, 2008


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Microwave HT fuse was replaced and working for a few days then blows again!

Forget the control board as that has nothing to do with the hv fuse and if that is blowing then the board is turning the magnetron on. The only things that will cause that to go are the hv cap, HGV transformer, hv diode or magnetron. Usually I would look at the cap and diode first as likely culprits but when they go they normally just go open circuit on the side and short on the cap all the time although could be breaking down under load. The most likely things that break under load intermittently in my opinion would be the magnetron which is just like an old fashioned valve in a magnetic field or the insulation layers in the transformer.

Please be extremely careful as the parts you are playing with are high voltage and the cap can kill you even when unplugged as if the discharge resistor had gone will remind charged and ready to discharge through you at high current like an electronic ignition system does on a car so always discharge the cap but touching an insulated handled screwdriver or pliers across its terminals before touching them. It will make a loud pop sound when it discharges. Only do so when unplugged.

Aug 02, 2017 | Microwave Ovens

1 Answer

I have a panasonic microwave with convection oven, grill and steamer. When I switch on the microwave, the house fuse (16 amp) cuts out. With the other functions of the oven, it works fine. Do I need a new...

you have a short circuit.
test the a) HV rectifier b) Capacitor HV c) HV transformer d) Magnetron e) test the swich for door for short.f) circuit board main is short.
see the diagrams and proceed.


Oct 01, 2012 | Panasonic NN-C994S Convection/Microwave...

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My microwave will not heat model #mw8119sb

Hello there and welcome to fixya
Testing the magnetron WARNING: First, with power disconnected, discharge the high voltage capacitor. See the section Safe discharging of the high voltage capacitor.
  • A magnetron with an open filament will result in no heat but no other symptoms. The bad connection may be internal (in which case the magnetron will need to be replaced) or external at the filament terminals (which may be repairable).
  • A magnetron with with a short between the filament/cathode and anode will likely result in a loud hum from the HV transformer and/or magnetron when the cook cycle is initiated but the main fuse will probably not blow. However, note that the actual wattage drawn from the power line will probably be much lower than under normal conditions. Although there will be a high current flowing in the HV transformer secondary through the HV capacitor (likely causing a loud hum or buzz), the real power consumed will be reduced since the current and voltage will be out of phase (due to the series capacitor) and the power factor will be low. A reading on an AC line wattmeter of 300 W compared to the normal 1,200 to 1,500 W would be reasonable.
  • A magnetron with other faults may result in a variety of symptoms including erratic or low output power or intermittent operation. See the section: Comprehensive list of magnetron failure modes.
There is no totally definitive way to determine if a magnetron is good without actually powering it under operating conditions but the following tests will catch most problems:

  • Magnetron filament. The resistance should be infinite from the filament connections to the case and a fraction of an ohm between the filament terminals with the wiring disconnected from the magnetron. While measuring resistance from filament chassis, gently tap the magnetron to determine if there is an intermittent short. However, such problems may only show up once the filament heats up and parts expand.
    It may be possible to determine if the magnetron filament is actually working by connecting just the filament connections to a low voltage high current supply on a Variac (e.g., a microwave oven transformer but just the filament connections). Most ceramic insulators are translucent and should show a glow with a working filament. The one at the antenna may be visible if the magnetron is removed from the oven or with a dental mirror looking into the waveguide. WARNING: Make sure you ONLY have the filament connected!
    I tried powering the filaments of a few magnetrons. On those that had white or pink ceramic insulators between the antenna cap and body of the magnetron, the glow was very bright. Even on one with a dark red insulator, the glow could be seen with the lights out.

  • Evidence of arcing (visible blackening around ventilation holes in base or burnt odor) usually indicates a bad magnetron.
  • Melting or other damage to the antenna cover ('bull-nose' or 'bullet') may be the result of arcing due to problems in the oven cavity or waveguide (perhaps operating with nothing in the oven) or a defective magnetron. (This part is only visible with the magnetron removed from the oven). If a problem elsewhere has been corrected, the damaged antenna cover can be pulled off and replaced from a magnetron that died of other causes - try your local appliance repair shop. (The shape doesn't matter as long as it fits tightly - there are several diameters, however.) Your magnetron may still be good.
    Note: Since the antenna is attached directly to one of the vanes which is part of the anode assembly, it will test as a dead short to the case on your multimeter using DC and is normal. At 2.45 GHz, this won't be the case! :)

Aug 17, 2011 | Emerson Microwave Ovens

2 Answers

Mirowave hums and does not make things hot....Convection oven seems to be fine

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

Microwave Oven Basic Troubleshooting Tips


Apr 20, 2011 | Microwave Ovens

1 Answer

Model 721.64282 microwave/convection oven - microwave not heating and making a loud noise. convection oven works

No heat but otherwise normal operationA shorted HV diode, magnetron, or certain parts of the HV wiring would probably result in a loud hum from the HV transformer but will likely not blow the main fuse. (However, the HV fuse - not present on most domestic ovens - might blow.)
If the main power fuse is located in the primary of the high voltage transformer rather then at the line input, the clock and touchpad will work but the fuse will blow upon initiating a cook cycle. Or, if the fuse has already blown there will simply be no heating action once the cook cycle is started. There are other variations depending on whether the cooling fan, oven light, and so forth are located down stream of the fuse.

Some models may have a separate high voltage fuse. If this is blown, there will be no heating but no other symptoms. However, high voltage fuses are somewhat rare on domestic ovens.

A number of failures can result in the fuse NOT blowing but still no heat:

  • Bad connections - these may be almost anywhere in the microwave generator or the primary circuit of the HV transformer. A common location is at the crimp connections to the magnetron filament as they are high current and can overheat and result in no or intermittent contact. See the section: See the section: Testing the magnetron.
  • Open thermal protector - usually located on magnetron case. Test for continuity. It should read as a dead short - near zero ohms. See the section: Testing thermal protectors and thermal fuses.
  • Open thermal fuse - some ovens have one of these in the primary circuit. It may be in either connection to the HV transformer or elsewhere. Test for continuity. It should read as a dead short - near zero ohms.
  • Open HV capacitor - see the section: Testing the high voltage capacitor. A shorted HV capacitor would likely immediately blow the fuse.
  • Open HV diode - see the section: Testing the high voltage diode.
  • Open magnetron filament - This failure may also be due to loose, burnt, or deteriorated press (Fast-on) lugs for the filament connections and not an actual magnetron problem. See the section: Testing the magnetron.
  • Open winding in HV transformer. See the section: Testing the high voltage transformer.
  • Defective HV relay. A few models use a relay in the actual high voltage circuitry (rather than the primary) to regulate cooking power. This may have dirty or burnt contacts, a defective coil, or bad connections
  • Shorted HV diode - see the section: Testing the high voltage diode.
  • Short or other fault in the magnetron - see the section: Testing the magnetron.
  • Short in certain portions of the HV wiring. See the section: Testing and repairing the wiring and connections.

Depending on design, a number of other component failures could result in no heat as well including a defective relay or triac, interlock switch(s), and controller.

If you are interested in doing it yourself the following link will help : Microwave Repair Manual

(**All the above references to tests are found here)

Oct 21, 2010 | Kenmore 63663 Microwave Oven

1 Answer

Just replaced the magnetron in my Panasonic NN-S543BFR. I still don't get any heat from my oven. Everything works as set but still no heat in oven. Need suggestions on repairs.

When you say "Everything works as set" do you mean the microwave appears to function properly, but then doesn't heat?

If the magnetron is new, then the magnetron must not be receiving the required high voltage (2000V or more) from the HV circuit. Make sure you've got 120V to the PRIMARY (don't attempt to measure secondary voltage of the HV transformer without special equipment) of the HV transformer. After that check the HV capacitor and diodes. If these components test OK, then either your HV transformer is bad or your new magnetron is faulty. My experience is that the problem is usually in control circuitry, preventing 120V to the HV transformer, or opens/shorts in the HV components (diodes and capacitors).

Mar 15, 2010 | Panasonic NN-S543BFW Microwave Oven

1 Answer

Ge Spacemaker microwave jvm240 wv Micro hood combo.

sounds to me like the magnatron has shorted out. i don't know of a way to test them unless you have some high dollar equipment. a continuity test prob wont tell you anything. what reading did you get on the cap when you tested it?

Jan 05, 2008 | GE Spacemaker JVM1640SJ Microwave Oven

1 Answer

Repairing Sansung Microwave version CM 1029

first check voltage to hv transformer if volts probably loose contacts on magnetron ,cap ,diode if still change magnetron

Mar 18, 2007 | Bosch HMT9626GB Microwave Oven

4 Answers

GE Microwave problems after HV capacitor replacement???

The rectifier diode could indeed be bad. But first I would want to know what value (in uF) the old one was and what is the value of the new one? If they're too far off, the difference in the capacitive reactance could throw off the "tuning" of the circuit. The uF value of the capacitor is optimized in relation to the other components used in the system. Of course, you'd also want to be sure your new cap is at or slightly above the working voltage rating of the old one, too.

Jan 04, 2007 | GE JVM2050 Microwave Oven

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