• ** 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

    Jake
  • Please note, some of the links on our site are affiliate links (Learn More)

FIXED KHMS147HSS1 KitchenAid Microwave - Exhaust Fan and Hood Light Switches Operate Reversed (Possible Cause?)

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Model Number
KHMS147HSS1
Brand
KitchenAid
Age
More than 10 years
All,

I appreciate the assistance. I have the aforementioned microwave installed in 2000, which worked great and is a smaller profile than most today, especially considering current availability of new.

About a year ago, the exhaust fan switch and the hood light switch started operating in reverse order and not accurately. For instance, you would push the exhaust fan switch and the light functions would appear on the display or vice versa. They also would not completely control the function. You have limited selections on the power level of each item. No service had been performed on the microwave and everything else works fine, including the actual mechanical output of the exhaust fan and hood light.

Now, the magnetron has failed and I am considering replacement. However, I need to know if the above issue is control board related or a simpler fix. I don't want to replace magnetron if the control board is failing since I don't believe it's available.

Has anyone seen this behavior or have any ideas? I couldn't find any instances in web searches or a quick look of the last 15 pages in this forum. I will repair if this item is correctable. Thanks again for the help.

Best,

Mac

Corrected model number
 
Last edited by a moderator:

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
42,585
Location
Murray, Utah 84107, United States

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Thanks so much. I was afraid of this. Twenty years is a pretty long run!

I have seen refurbished boards for sale or you can send in one for inspection. Is this advisable to explore? I've used rebuilt auto electrical parts but have no idea if it's a wise practice with these sort of things.

It looks like it's going to take months to get a new unit of preference. Thus, I've got time, and I really love this unit.

I know...probably best to cut it loose at this point with magnetron, board, and whatever is around the corner.

Best,

Mac
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Thanks. I found a few sources for the control board that appear to be reputable and have the correct item.

I believe I read somewhere that RF leakage from a failing magnetron could reach the control board and cause erratic behavior.

Is this possible and if so could it apply to my case? It seems this would be rare if it does occur.

If I do repair this 20 year old microwave with new magnetron, diode, and refurbished control board, is there anything else that I should replace while I have it off the wall such as the power supply or HV capacitor?

Appreciate the thoughts.

Best,

Mac
 

Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
120,426
Location
McMullen Valley, Arizona
Hi Mac,

Rick had to go out of town, he can finish assisting you when he returns.

Jake
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
42,585
Location
Murray, Utah 84107, United States

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Thanks again. I'll open it up and see what I find now that you guys have given me the info to make a plan.

If I get stumped, I'll reach back out, and I will report the final outcome.

Best,

Mac
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Well, I opened it up and got to testing. The HV power supply and capacitor tested good. I pulled the magnetron. It tested good on the filament, but showed resistance on the casing measurement. I guess this was the problem as expected. I did not go to the trouble to test the diode, but it certainly looked aged. Thus, I will replace it as well. I ordered a control board from a reputable source on ebay. It looks to be the exact item in its FSP original box sold as "OEM Board removed from new cosmetically damaged unit". The prior buyers of item reviewed it as described.

One thing I can say for sure, after trying every version of Torx driver I could find, is that there's only one way to get to the magnetron and one way to get it out. The front air flow duct plastic piece behind the control board has to come out to reach the magnetron screws. Ultimately, I just manhandled the air duct out, and it looks no worse for the wear. There may be a more elegant way, but it would have required more disassembly. At first , it didn't think the magnetron would come out after unscrewing, but at the perfect angle, rotation, and force it pops out. The control board has way more connections than I expected. I'm going to have to be very meticulous in replacing it with lots of pictures and maybe a second set of eyes.

I don't know how you guys remember all these intricacies when working on hundreds of different units. My applause to you!

I'll let you know if I get it going. Right now, I'm rolling the dice and being judged by the head of the household. My only solace is that we probably couldn't get a similar unit until late December or next year.

Best,

Mac
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Good point. I guess I should have said "appears as reputable as you can check for these sources". I'll have to keep my fingers crossed as this board is only available from these types of sources from my searching. They all looked to be about the same level of risk.

I'll inspect closely on arrival and keep the existing board, which does maintain basic functionality. Perhaps, it might have something obvious that could be repaired.

Best,

Mac
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
I did get the oem magnetron, diode, and 2 ignitors for my gas oven from APP. I've purchased a lot of parts from them over the years, even before reading this forum. I've had nothing but positive experiences. I am a regular shopper for ignitors! We use the oven daily.

Best,

Mac
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Got all the HV parts from APP and have tested/installed HV components.

I am working on the salvaged control board, which looks to be the correct model with appropriate markings. It appears to be unused (hopefully not a factory reject) as the break-off pieces of board are still intact. They dummy section runs along one vertical side of the board and contains individual break-offs for display, selector, etc.

I'm assuming since these are very lightly scored on both sides (not grooved) that they can be broken off carefully by hand. Since some pieces are printed, would it be best to carefully score further or go straight to breaking on a straight edge of some sort?

My problem with the original board was overlapping exhaust fan/hood light control. I noticed in the service diagram that these functions are number 1 and 2 on a 12 Pin flex circuit connector. However, the flex connector ribbon is part of the touch membrane assembly and not the control board itself. Could my original problem have be the ribbon itself or a loose/shifted connection? Anything to look for on the ribbon to indicate problem or a process to clean it, etc? Appreciate any insights on this part of the repair and what might have been the original issue.

Lastly, do you align then fully seat the ribbon in the middle of the locking connecter before snapping in the locking bar of the connecter to complete the connection? It looks pretty straightforward, but I thought I would ask.

Thanks so much for your input and assistance. Its really appreciated!

Best,

Mac
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
42,585
Location
Murray, Utah 84107, United States
We don't go past board level and I don't have any information on boards, sorry.
 

Macpage

Premium Member
Joined
Sep 30, 2020
Messages
11
Location
USA
Thanks Rick. You had it right from the beginning. The control issues must have been the board. Once I installed the replacement board and the new HV components the unit powered up fully functional. I was surprised at just how quiet it was with newer parts. We've had a couple of days with no issues and have the unit back on the wall. The new board separated easily with hand pressure, and the 12pin flex connector seated and mounted easily. We just had to label a lot of wires to make sure we got it connected correctly.

Really, the biggest challenge was putting back all the parts with brittle 20 year-old plastic hooks/tabs. At some point in disassembly, I must have broken 2 hooks on the control panel mount. I had to use Hvac tape to tape the edge of the panel to the inner frame of the unit before replacing the exterior cover. It turned out fine, but the control panel will never come off without removing the unit from the wall :).

The upper vent/grille assembly was a real pain. This original design seems to be notorious for plastic mounts and tabs failing. Ours was still original, and it broke in multiple places on removal. Actually, it just fell off in my hand when I went to remove it. It had broken at some point in time and was just sticking to the frame with old cooking residue. I used lots of super glue, some hvac tape, and a toothpick to get it back on and spaced correctly! As it's stainless, we were glad to have been able to salvage it. It's one expensive part if you want to stay with that look.

We are happy. We saved over half of what a new model with this look would have cost, and we didn't have to wait 3 months. We really appreciate your help Rick, the good service from APP, and the fine folks administering the blog. It's nice to have folks willing to help out with these repairs and to be able to keep an appliance in service. Thanks again for everything.

Best,

Mac
 
Top