RE: Samsung microwave SMH7187STG mfg'd 5/08. I heated cup of tea 2 min.Then I closed micro's door & micro emitted a continuous electrical buzzing sound.I opened door & buzzing stopped.

the main component..the magnatron..has flown south...you can research the part number by taking the back off and physically taking the number off the part..or research it by make and model..parts.com

First, check to make sure that the door is closing and latching fully and that there is nothing jamming any of those mechanisms. There are safety devices that keep microwaves from turning on if they think the door is open/ajar.

If the door is fine and the rest of the functions (timer, etc.) are behaving, it's probably a busted magnetron. That's the part that actually emits the waves that do the heating. It's a part that can be replaced, but probably cheaper to get a new microwave.

Here is a simple power test.
Place a measured cup of water into the microwave. Run the micro for 2 minutes. A 1000 watt micro will boil a cup of water in 2 min. Check the power output of your machine. It will be found on the model number tag. A 700 watt micro will take about 3 minutes. If this occurs, the machine is working properly.
Otherwise, check the outlet voltage, should be 110 or higher.
Outside of this, you could need a high voltage capacitor or magnetron.

check the door safety interlock switches. if failed, they cannot tell the oven that the door is closed and if the door is open, the magnetron will not come on. remove the cover and find the small micro switches neat the door latch system. check them with a ohm meter with the door open ... then closed. of course, you are checking for continuity ...not voltage ... so unplug the oven before you start.

Hi,
Place you cup of water in the microwave with the tea bag in the cup....The run the microwave for 30 - 1 min. just like you were heating the water...

heatman101

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

Basic Microwave Oven TroubleshootingTips

heatman101

it sounds like it one of your micro-switches inside that control the power to the doors, if one of the switches is bad, it would cut the power , the panenl will light, the turn table will work, the fan will turn on , but you will not get any heat at all, micro-switches run depending onthe unit from 5-10 bucks, when you open the unit you will see the one that is bad, is usually bent or the connector might be burn or melt, good luck..!

Do you have the new handle already? I need a whole new door due to a scratch and will have a new handle from the scratched door that I wont need........

You can check the relay and related driving circuit. If there is a short in the relay driving circuit there is chance for this type of problem. or the micro processor may be defective.

There are three solutions (source) =>

http://www.partselect.com/repair.aspx?appliance=microwave&part=no-heat

Power Diode

A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.

High Voltage Capacitor

A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating but you are hearing a buzzing or humming noise. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.

Magnetron




A defective magnetron is the third possible cause of why your microwave is not heating, but you can hear a buzzing noise. Test your microwave's magnetron. Replace it if it is defective.