Question about Whirlpool MH1150XMQ Microwave Oven

2 Answers

Poor heating performance

We noticed that the oven wasn't heating things very fast. I checked the AC voltage at the outlet the oven gets its power, and I see the line voltage drop from 117 VAC to 106 VAC when the magnetron is on. I don't seem to hear any fan noise when the magnetron is on, and I recall that a fan used to be on when the magnetron was operating. If I run the oven on 20% power, the magnetron cycles on and off, and when the magnetron is off, the line voltage returns to 117 VAC.

I ran the heating test described in the repair manual hidden in the top of the oven, and for the reduced AC voltage case the oven heated 32 oz of water by more than 19 deg F in 60 sec at full power.

So, why is the oven drawing down the line voltage so much & seemingly heating food poorer than before?



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  • treborg55 Jan 24, 2008

    I didn't mention that the water heating test result means that the magnetron output is normal for the reduced AC voltage according to the repair manual, so I'm doubtful that the magnetron is bad. After some thought, I now suspect that the cooling fan motor has shorted out, causing the excessive voltage drop. It doesn't look like I can get to the fan motor without dropping the microwave off the wall. Is that correct?

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2 Answers

LINE VOLTAGE WILL DROP IF THERE IS TOO LONG A RUN OF ELECTRICAL WIRE FROM THE SOURCE TO THE OUTLET
OR IF THE WIRING IS UNDERSIZED. THE 13 AMPS A NORMAL MICROWAVE DRAWS SHOULD NOT DROP THE VOLTAGE THAT MUCH. IF YOU HAVE A CLAMP AMP PROBE
PUT IN AROUND THE MAIN BLACK LEAD OFF THE PRIMARY
FUSE AND SEE HOW MUCH CURRENT IS BEING DRAWN WHEN THE MAG TUBE IS ENERGIZED. SHOULD NOT BE OVER 13 AMPS. IF AMS ARE O.K. SUSPECT HOUSEHOLD CIRCUIT.

Posted on Mar 28, 2008

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  • Master
  • 579 Answers

I complement you on an exemplary report!
The drooping line voltage seems a little more than desired and you might want to try it on a different outlet, but doubtful the real problem. Microwave ovens are about the heavyist load that standard house wiring sees.
More likely the magnatron is just going bad especially if the fan hasn't been working and it has been running hot.
By the way, how old is it?
They are not too hard to replace yourself. Look on EBAY for "universal magnatron"
Hope Ya Fix it!

Posted on Jan 24, 2008

  • Greg Collins Jan 24, 2008

    The fan hardly draws any power, even if it fails.

    But yes, take it off the wall and try it on a different wall circuit.

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1 Answer

Code f-33


Step 1:

Symptom: Intermittent or continuous error code F33 on the display. Cause: Insufficient (poor) grounding of the controller (DP) board.Remedy: clean the groundHowever if Not Heating proceed with the next steps.

1)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. A regular meter with a diode checker will not work to check these diodes. You have to use a meter with a 9 volt battery or put a 9 volt battery in series with the diode to check it.
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 testin
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. When a high voltage transformer fails it will usually arch and have a burning smell
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.

Step 2:

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Step 3:

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1 Answer

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1 Answer

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If it is resetting, there is a chance that the problem is not with the microwave but the AC supply. These units draw a bunch of current and if there are any sloppy connections or a bad outlet (if plugged in), the connection can fail long enough to drop the AC input far enough to turn the unit off.
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9 times out of 10 this is usually this is a bad magnetron, the other time is sometimes a bad high voltage diode. See components section. Q - My microwave is running and sounds like it is working but will not heat up anything.
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Q - My microwave is running and sounds like it is working but will not heat up anything.
A - Many thing can do this but, common things are....loose high voltage wire.....poor solder joint on board.....magnetron.....power relay.....
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If it is working but not heating, then test the high voltage capacitor,the rectifier diode.or the magnetron. If all this are fine, test the control board.

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



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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.

You can also order from MicrowaveSvc , they also provide parts.

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