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Micro doesn't heat

Panasonic inverter NN-ST756W runs but does not heat. It also stops early sometimes. High voltage diodes apear to be open circuit.
Can you buy the diodes or the whole module?
Thanks

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  • kendb Mar 08, 2008

    Thanks Maklean, I've measured the high voltage diodes and they are open circuit so I'll start by replacing them. I was wondering what may have caused them to blow?

  • wantpopcorn Mar 24, 2008

    I have a Whirlpool microwave oven. It runs (makes the noise of running) but is not heating. It has done this before after a power outage and I unplugged it for long enough to reset it and plugged it back in. It worked fine for a while...off and on with the obove issue. Now, can't get it to heat at all. I've taken it down and taken it apart, but don't really know what heats it or what would cause this issue. I located the Tech Sheet, but this hasn't helped me so far.

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When the microwave sounds okay, but there's no heat, one of the internal door switches, the high voltage circuitry, or the circuit board may have a problem. To resolve this problem, you need the assistance of a qualified appliance repair technician.
See PartDetective

Posted on Mar 08, 2008

  • Kleanthis Mavropoulos
    Kleanthis Mavropoulos Mar 08, 2008

    Select brand=panasonic, appliance type=microwave insert item number at the search tab. i.e. 940337 and click "search"

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1 Answer

Panasonic Dimension 4 Microwave- Model NN D801. Whilst microwaving for 2 mins on high - heard a zapping noise. Didnt heat food. Front operating panel works. turntable still works. Any suggestions?


A "zapping noise" usually indicates a problem in the high voltage circuit. If it's an inverter oven, it should have provided you with a fault code. If a non-inverter, the most likely causes are a shorted high voltage rectifier or bad magnetron. But there are many other possible causes.

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1 Answer

Sharp micro doesn't heat


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 02, 2012 | Sharp Microwave Ovens

1 Answer

My microwave Panasonic NN-K544WF is not heating the food otherwise it is working


It sounds like the magnetron may have either failed or is not being supplied with the extremely high voltage required to run it.

Assuming this is not an Invertor type.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 on high resistance range for short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.

Dec 16, 2010 | Panasonic Microwave Ovens

1 Answer

Microwave works but does not heat on any power setting


The magnetron may have either failed or is not being supplied with the extremely high voltage required to run it.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 on high resistance range for short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.

Dec 09, 2010 | Panasonic NN-S753 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).

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1 Answer

Micro wave made a popping noise now does not heat up food as hot


The popping noise was probably the capacitor or high voltage diode blowing.

Test the high voltage capacitor, the rectifier diode.or the magnetron.

The diode and capacitors can br tested. The capacitor must be allowed discharge before testing, or you risk to get electrocuted, even if power is off. Capacitors can get discharged by shorting their two contacts.
Replace the magnetron if the checks and all of the high voltage component tests are good, but the unit still does not heat.

All locations, and description of this parts can be located using the diagram here: Counter top.

Parts must be tested to find out what is wrong.

Remember that microwaves are potentially dangerous devices if not repaired properly, the job must be done by a competent person.
A microwave energy leakage test must always be performed when the oven is serviced for any reason.

Regarding parts, contact the seller here to purchase parts.

Apr 08, 2009 | Panasonic NN-C980 Convection/Microwave...

1 Answer

Panasonic nn-sn667b 1300w dead


You might consider just replacing the inverter assembly itself.

It will cost more than replacing the bad discrete components of course, but you would be avoiding the time and money involved in parts research, trial and error, and possible destruction of any newly installed parts if there remain other undiscovered defective components.

The inverter assembly (part # F606Y8M00AP) can be had for $79.12 here.

Otherwise, you would need to order the service manual, which is not listed by the major Panasonic distributors.

The service manual should be # SM-NNSN667.

The best place to order Sharp parts is Tritronics. Or you can call them toll-free at 866-779-5835.

In this case, call might be more productive to track down the service manual.

Good luck, and be safe.

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

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You may have a shorted High voltage component. Possibly a recttifier,aka, diode. This should only be replaced by an experienced repairman as an extremely high voltage shock potential exists.

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because of high voltage circuit thats happend ,please check highvoltage circuit may be short circuit or any companent burntout. check magnetron and high voltage diodes etc.

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