• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

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Samsung Microwave humming sound when first plugged in


Premium Member
Jan 29, 2013
Broomfield, co.
Model Number
1-5 years
I am trying to help my daughter figure out if she is having trouble with her Samsung microwave Model SMH7187STG. I have the unit on my bench right now. When I first plugged it in there was a humming sound coming from the cabinet as if the magnetron was engaged, so I unplugged it and tried again several times. After about the fifth time I left it plugged in and proceeded to program clock, date and so on, after about two minutes there was a small pop or click and the humming stopped. I opened the door and felt the glass dish inside and it was very warm almost hot. Unplugged the unit waited five minutes and plugged it in again, no humming sound, checked the dish once again and it was not warm this time. I programmed the settings again and it seems to be working fine at this time, (controls work, light comes on, turntable turns, and it warms food or liquids). Do you think there was a problem that magically resolved itself? Should I continue testing or see if magic wears off and the problem comes back? ? I should have mentioned in the beginning that she called someone out to check the microwave (was suppose to be free check up) but they charged her $35.00 and told her it was a bad transformer and would cost &200.00 to replace it but they would not guarantee it would work. They did not say which transformer was bad.

Thank you for your help and suggestions.


Appliance Tech - Moderator
Staff member
Jul 11, 2006
Murray, Utah 84107, United States
mfhjr said:
Do you think there was a problem that magically resolved itself?
In thirty years I've yet to see anything fix itself. But with today's technology, who knows. Bad transformer plus no guaranty equals RED FLAG! I doubt the transformer is bad. In fact, it sounds like it's good if the mag tube turned on. What it sounds like to me is a stuck relay on the control board. When you press start the control board supplies the transformer with supply voltage by closing a series of relays. Now that it's working it might be difficult to diagnose until it happens again. Try to reproduce the problem by placing a large micro safe bowl in the oven with just water in it and heat on high for 5 minutes. Next time you hear the noise see if the primary side of the transformer is getting 120 VAC or use an amp probe around one of the mag tube wires. If the transformer is getting 120 VAC without programming or pressing start the control board is most likely the problem.