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Whrlp Master Tech
Whrlp Master Tech, Whirlpool Master Technician
Category: Appliance
Satisfied Customers: 10179
Experience:  30 years Appliance Field 15 yr with Whirlpool Corp. 9 yrs Whirlpool Technical Assistance Line
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Hi I have a KitchenAid KHMS155LSS-4 Stainless Over the range

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Hi I have a KitchenAid KHMS155LSS-4 Stainless Over the range Sensor cook Microwave that I purchased back in 2/15/2007 ..... it was a fairly expensive Unit ( Purchased for $499 on sale marked down from $650.00. Anyway it quit heating about a week ago & makes a loud humming noise when it first starts then that stops & everything goes on as normal ( lights work, Turntable spins, fans work, etc ) except no heating.....I ran the Code test from the key pad and all passed so I am wondering if anyone has any idea of what this is or would cost to fix.
I believe the Magnatron is still covered under KitchenAids warranty but that is probably all that is covered for parts & I have no way of figuring out if that is it or if it is a Capacitor or something else. Any help would be appreciated cause I am trying to way out if worth fixing or having to purchase a newer less expensive model
Thank You in advance

From what you are saying with the loud humming noise .

I would suggest replacing the capasitor and the diode .

the diode .Number(NNN) NNN-NNNN$4.07 capasitor(NNN) NNN-NNNN$38.97


items 19 and 20 ategoryId=0123370&brandId=0593&brandDescription=KITCHENAID&modelName=MICROWAVE-HOOD-COMBO&diagramPageId=00003&componentDescription=INTERIOR%20AND%20VENTILATION%20PARTS&documentId=W0601206&blt=06


Customer: replied 7 years ago.
I see you Quoted me Whirlpool Parts ( Capacitor & Diode ) for my KitchenAid Microwave....... are those parts interchangeable???
Also seeing that this is a over the range microwave are those parts something I can get at without removing the unit from its elevated position over the stove or do I need to take it down to get to those parts to change?? Also could you tell me why either part ( Diode or Capacitor) would cause the machine to make that loud buzz or humming sound on start up? Is there any other part that could cause that? Reason I ask is because it would be worth me fixing this unit then over purchasing a new one even if I had to have a tech come out to discharge the Capacitor and install the parts. Let me know
THank You

Whirlpool makes and owns Kitchen-Aid. the only thing differant about the two is just the name and the price.

The cap or diode being bad makes the tranformer (load up) Strain.

yes the unit has to be taken down and have the outer Wrapper (cover) taken off


Yes would be better to repair then replace.

and no other parts will cause the humm we call it a GROWL.

Customer: replied 7 years ago.
1 last question for you...... How Difficult is it for me to discharge the Capacitor to change out these 2 parts? : ) Is this something I can do myself? I know you don't know my background & I am not a Certified Tech but I do have a good understanding of electricity.....not that that quailifys me but if it is a simple change I know I can handle if not let me know.

Thank You again

yes you can.

Just turn power off and on the terminals of the capasitor ,just go across one of the terminals to the capacitors grounded chassis.graphic

Whrlp Master Tech and 2 other Appliance Specialists are ready to help you
Customer: replied 7 years ago.
Perfect, thank you for all your help & I will accept your answers now so you get paid. : )
no problem ,thank you and have a Happy New Year
Customer: replied 7 years ago.

Hi, Ok as per our convo on 12/29 I ordered the H.V. Capacitor & Diode as you sugested from Repair clinic. Installed both parts and my Microwave does the exact thing it did before........( Makes a Loud humming/vibrating sound when turned on -- see above in original post for make, model & original questions) so my guess would be that it was not either of those parts as the same problem still exists ( no heating & loud humming/Vibrating noise when running) so do you have any other suggestions on this before I send back the H.V. Capacitor for a refund??? If it would help i could upload a YouTube vid so that you can hear this for yourself otherwise I am going to call it a loss and send back the parts & purchase a new model which I was trying to avoid........please let me know what you think as I have the microwave all apart & am trying to decide which way to go on this. Thank You Alan

I my 30 year of service if you have a loud growling/hum it is either the cap or the diode ,

Make sure you installed the diode terminals properly on the cap and the ground screw is tight.

to test the Magtube pull one of the terminals off and run it to see if the hum is still there .

Ive never seen a mag tube make a humming noise ,but you can test it if you want .

If you have a loud noise I can`t see it is a high voltage transformer issue or it would not even make a noise at all.

Customer: replied 7 years ago.

Hi, I took Pictures before I removed anything then installed the Diode & H.V. Capacitor. Both were installed exactly as they were originally. I rechecked the both ( Diode Ground Screw & it was tight as was the strap screw holding the HV Capacitor) Now the only thing I didn't do was re-attach the wrapper/Cover when I tested it because I didn't want to put it all back together & have a Problem ( didn't think that would matter seeing that it was not attached as a direct ground or anything. ) but let me know if for some reason that would be a problem. I will pull a wire off the Magtube as you suggested and see if the humm stops ( doesn't matter if red or white wire right? )

Thank You.

Customer: replied 7 years ago.
Ok, I did as you said ( Unpluged 1 wire from the Magtube ) and it still made the same noise so I uploaded a short clip to YouTube so you can actually see and hear this( ) ( sorry about the lighting but my camera practically needs a pure sunlight to record well but the sound is what we want to hear anyway right? ) Also it took about 2 minutes for the noise to start humming/Vibrating after I first started the unit ( with or without the wire hooked up.....hope this info helps along with the vid on Youtube so maybe we can figure this out....... I really do appreciate all your help on this.
Thank You Alan

Thank you fro the video ,it sounds like the transforner is loading up .

And this is the same noise you have when the wire is on the magtube correct?

Customer: replied 7 years ago.
Yes, it is the same noise when the wire is on the Magtube & when it is unhooked from the Magtube. Does the Transformer then need to be replaced? I didn't see transformers offered on Repair Clinic for my model so not sure of costs or if its worth replacing if that is the problem. So if the Transformer is loading up where do I go from here?

Thank You

here is the link to the transformer


Customer: replied 7 years ago.

Well Thanks for all your help. Without the ability of being able to test the HV Transformer & your original comment of... "If you have a loud noise I can`t see it is a high voltage transformer issue or it would not even make a noise at all" that says to me that it is possibly not the transformer either which could end up costing me more time & another possible return so I am going to cut my losses & send back the original parts & go ahead and purchase a new unit.

Thanks again
ok sorry we could not get it up and running.