Has anyone ever heard of a microwave oven turning ON when opening the door?

Thread Starter

rkkeely

Joined Jul 29, 2017
8
I have a Samsung model SMH9207ST OTR microwave oven that is about 4 years old. Everything works fine except the mw oven now turns ON by itself when you open the door?? (Inside light and fan come on - not sure if it is microwaving). Weird! Any suggestions on what is most likely wrong would be appreciated.
 

Dodgydave

Joined Jun 22, 2012
9,322
The microwave has three interlock microswitches on the door lock, and one of them shorts out the hv supply to the magnetron for safety, sounds like something has gone duff around the door lock.
 

GopherT

Joined Nov 23, 2012
8,012
I have a Samsung model SMH9207ST OTR microwave oven that is about 4 years old. Everything works fine except the mw oven now turns ON by itself when you open the door?? (Inside light and fan come on - not sure if it is microwaving). Weird! Any suggestions on what is most likely wrong would be appreciated.
Some commercial microwave ovens (like for DIY hotdogs at the gas station) turn on the fan when you open the door so you don't smell the rotting spatter from the previous 20,000 meals made in there.

I have not seen a home microwave do that. Check the current draw when you open the door if you happen to have any tools. Over 75 watts will be a concern.
 

Alec_t

Joined Sep 17, 2013
11,552
Welcome to AAC!
It is usual for the light, but not the fan, to come on when the door opens (light on but not fan with my Sharp oven).
The magnetron should be off with the door open. You could check with a microwave leakage detector or a jar of water; but stand well clear to avoid being cooked :eek:.
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
Thanks DodgyDave and Dennis for the quick replies. I'm just thinking that even IF it seems there is a problem with the microswitches/door switches, it seems the control board must be bad also (else why would it be telling the mw to turn on?)

Thanks,
Randy
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
Some commercial microwave ovens (like for DIY hotdogs at the gas station) turn on the fan when you open the door so you don't smell the rotting spatter from the previous 20,000 meals made in there.

I have not seen a home microwave do that. Check the current draw when you open the door if you happen to have any tools. Over 75 watts will be a concern.
Thanks GopherT - will do.
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
Welcome to AAC!
It is usual for the light, but not the fan, to come on when the door opens (light on but not fan with my Sharp oven).
The magnetron should be off with the door open. You could check with a microwave leakage detector or a jar of water; but stand well clear to avoid being cooked :eek:.
Great idea since I don't have a leakage detector! Thanks!
 

Tonyr1084

Joined Sep 24, 2015
4,933
One of the quickest ways to determine if your microwave is waving when the door is open is to put a CFL light bulb inside the oven. Don't turn the oven on, just open the door. If the light bulb glows then quickly close the door and unplug the unit. It's time for a new oven. If the light bulb does NOT light then there are no microwave emissions.

The light and fan should operate independently of each other. It's possible you're getting the light and fan because some grease may have bridged a circuit or two on the board, causing the oven to think the fan needs to be on. Do you know there are TWO fans in a microwave oven? One for exhausting the oven from smoke and fumes and the other fan is to keep the magnetron cool. They are independent of each other. You might be hearing the exhaust fan but you don't usually hear the cooling fan.
 

Tonyr1084

Joined Sep 24, 2015
4,933
You could check with a microwave leakage detector or a jar of water; but stand well clear to avoid being cooked
Standing clear is GOOD advice. If you double the distance from the oven you expose yourself to four times less microwave energy. There are three ways to reduce exposure to radiative energy; 1) Shielding; 2) Distance; 3) Time of exposure. If your oven is one of those plug in units that sit on the counter then unplug it before you open the door. Put the light bulb in there, plug the unit in then briefly open the door. The door will act as a shield and limiting your time will further reduce the risk. KEEP THIS IN MIND - ANY EXPOSURE IS TOO MUCH. So don't assume you're safe if you operate a defective oven. Who knows what else may go wrong with it. The jar of water may take time to boil for you to know the oven is radiating. The light bulb will give you an instantaneous indication. Water is good advice, but I think the light bulb is a brighter idea.

˚J˚
˘
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
Great advice AlecT and Tonyr - Thanks! The water did not heat after several minutes and the cfl light bulb did not light. Good news - not waving, but I still must have a control board problem. Thanks everyone for the help. Now I just need to order cb and figure out how to replace it. :)
 

ian field

Joined Oct 27, 2012
6,539
The microwave has three interlock microswitches on the door lock, and one of them shorts out the hv supply to the magnetron for safety, sounds like something has gone duff around the door lock.
The TS would probably have gone blind by now - but don't take anything for granted, microwaves are too dangerous to take chances with.

The whole point of the interlock switches is they should be fail-safe - if both break switches weld; the 3rd switch should short it out and blow the fuse. Blowing the shorting contacts isn't completely impossible.

A lot of microwaves power the light and fan when you open the door - mine does.

Mine has an iron cored transformer and the stray field makes the steel case buzz - modern SMPSU types probably don't.
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
Yep, thanks again TonyR and Ian. At least I know it's safe now to use until I can replace/clean the main cb. It's just weird bc the light always came on when you open door as it should, but now the fan turns on also - weird!
 

ian field

Joined Oct 27, 2012
6,539
Yep, thanks again TonyR and Ian. At least I know it's safe now to use until I can replace/clean the main cb. It's just weird bc the light always came on when you open door as it should, but now the fan turns on also - weird!
Doing something different for no apparent reason should be investigated.

Pretty sure you'd know about it if the thing fired up with the door open - but be vigilant!
 

GopherT

Joined Nov 23, 2012
8,012
Yep, thanks again TonyR and Ian. At least I know it's safe now to use until I can replace/clean the main cb. It's just weird bc the light always came on when you open door as it should, but now the fan turns on also - weird!
Also check your manual. There are hidden setup menus on some brands. I had an Amana in my old house, I could hold "1" button down for 5 seconds and a menu would be available where I could adjust features like, "reset clock on door open", beep volume, duration of "soup", "popcorn", "hotdog", etc

Maybe someone accidentally activated one about your fan.
 
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My over-the-range GE unit developed this same problem--open the door and the fan turns on. Apparently this is a known problem with this particular oven. I checked with a spectrum analyzer and there's no microwave emission; it's a real thing--fan comes on, no microwaves. It's old enough that buying a new one rather than fixing was the better choice.
 

Thread Starter

rkkeely

Joined Jul 29, 2017
8
My over-the-range GE unit developed this same problem--open the door and the fan turns on. Apparently this is a known problem with this particular oven. I checked with a spectrum analyzer and there's no microwave emission; it's a real thing--fan comes on, no microwaves. It's old enough that buying a new one rather than fixing was the better choice.
Thanks!
 
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