Kitchenaid KBMS1454RSS0 microwave cuts off and on when heating

[ChristopherW]

Model Number

KBMS1454RSS0

Brand

KitchenAid

Age

More than 10 years

This microwave is about 15 years old. It mounts in the wall and matches the rest of our Kitchenaid appliances. When in use, it will start and then stop, light goes off, fan stops, timer freezes, then it will start again. Usually worse when hot. Occasionally it will stop every 2 seconds and then run fine the last 30. Several years ago it was doing something similar. I opened up the cabinet and found 2 connectors that were burned. One was the blue wire at the HV transformer, coming from the relay and the other was the white wire from the magnetron thermostat to the cabinet thermostat connector. I replaced both connectors, cleaned up the terminals and it's been fine until a few weeks ago.

Recently, I replaced all the door switches, the HV capacitor and diode. I tested the thermostat on the magnetron which was fine. I'm starting to suspect the cabinet thermostat. I checked it and it was showing 2-3 ohms. I think it is supposed to be 0. The line filter capacitor is one other possibility, but I have not tested it yet. Parts are hard to find. The cabinet thermostat, Whirlpool part #8205652 is NLA. If I had the tech sheet or service instructions, maybe I could find a suitable replacement? I've checked the power coming in, which is fine. I would hate to scrap it over a $10 part. A replacement is about $1700.

Appreciate any insights or advice

 

[Jake]

Rick has been out sick since Jan.12th with a serious illness, we are hoping and praying for a speedy recovery!

Rick is our Microwave expert, so unfortunately you'll have to wait for him to return or hopefully another tech. like @jeff1 or @Dan O. or another member that's run across this problem, can help you here.

Jake

 

[Dan O.]

timer freezes, then it will start again.

The countdown freezes??

I do not know of any external factors that would pause a timer's countdown. Any thermostats or safeties would usually stop all functioning, either just heating or the whole unit (display and all) either permanently or until a thermostat reset. They wouldn't usually affect just the countdown.

My guess is there is a problem in the electronic control unless there is a setting that has a pause built into it. Check the owner's manual.

I did find a service manual. You can look at it and see if it mentions such a symptom. (BTW. There should be a tech sheet inside the appliance.)

JMO

Dan O.

 

[ChristopherW]

The countdown freezes??

I did find a service manual. You can look at it and see if it mentions such a symptom. (BTW. There should be a tech sheet inside the appliance.)

Thanks much for your help. I'll post what I figure out.

 

[ChristopherW]

Dan O., you had asked about the pause. It's like a momentary stop - light, fan and turntable all stop, timer stops at whatever the countdown is and then everything resumes until the next momentary stop or it finishes the cycle. Cavity thermostat could cause that? Or possible the line filter? Or could it be the control board is failing?

With the Service Manual I've been able to identify there are 2 cavity thermostats. One on top, which appears to test OK, O ohms and one on the bottom, that appears impossible to reach. Since it is in a series with the others, it could be the problem. Service manual identifies it as No load cavity thermostat assembly – opens at 257°F (125°C), closes at 185°F (85°C). If I can test it and it's bad, the Whirlpool part #W10852735 is available at least. Is there a reference somewhere to all these thermostats that shows their specs. Is suspect there could be suitable alternative that don't cost $100?

 

[ChristopherW]

OK, so the cavity thermostats both check out good, 0 Ohms cold. The lower one was a pain to access. The turntable motor plate is riveted to the bottom plate, so I had to grind off the rivets and remove the plate to access. The line filter shows 120V in and out in standby, but when running a cycle it drops to 114V or even 113V. Is that normal? I'll run a few cycles until is acts up and monitor the line filter voltage out to the system.

 

[Dan O.]

timer stops at whatever the countdown is and then everything resumes until the next momentary stop or it finishes the cycle. Cavity thermostat could cause that?

I do not know of any external factors that would pause a timer's countdown.

A power interruption would usually blank the display.


Dan O.

 

[ChristopherW]

A power interruption would usually blank the display.

After considerable test runs, I'm pretty sure the line filter is OK. I think its the power relay on the control board which shuts down everything except the timer. Of course the control board is NLA. I've seen at least one supplier that has availability

 

[ChristopherW]

So it turns out the control board 8206314 is NLA. None on Ebay. The new version of this same oven KMBS104ESS, looks nearly identical to mine. The same control board for that model, W10591452, looks identical to my board. Does Whirlpool have a cross reference for these control boards?
Also, I located a circuit board repair place, The Repair Shack. They said they can usually repair these boards, $119 + shipping.

 

[Dan O.]

Does Whirlpool have a cross reference for these control boards?

If a part could be substituted to an alternate the manufacturer would substitute the number before discontinuing it. If the original number doesn't substitute it most likely can't be but you could check with Whirlpool directly.

I have no knowledge of that repair service. That is about the going rate for other circuit board repair services.

Dan O.

 

[ChristopherW]

Thanks. I appreciate the advice. I mailed the board off today to The Repair Shack. While I'm waiting I'll ask Whirlpool about the two boards

 

[ChristopherW]

I received the control board back and installed it. The tech who repaired it stated the following: Main issue was failing power capacitors as well as engagement relays beginning to buildup resistance on contacts. Replaced bad relays as well as all lifespan-based components to help with longevity of unit. Power tested control board with no power fluctuations during extended testing, however function testing requires entire appliance.

Microwave is still not working right. I don't believe they replaced the microwave power relay on the board. I enclosed a short video on what happening

 

[Dan O.]

From the video, the display malfunction looks to coincide with the reversing direction of the turntable motor.

LINK > KBMS1454RSS0 Turntable Motor

As near as I can tell, that motor is powered directly from the electronic control. I don't know if a malfunctioning motor could be responsible for it. If it isn't the motor that is responsible I can only see the problem being in the electronic control which may be less likely since it was repaired. But I couldn't say either way with any certainty as I've never seen such a malfunction ever occur before.


Dan O.

 

[ChristopherW]

The one sensor I had not tested was the humidity sensor. The manual says 2800 ohms at 77 degrees. I get readings more like 3200 ohms. So it appears to be out of spec. Could that cause the system to start and stop? I tried running a cycle with no power to the HV transformer. Still did the same thing. I ran several cycles with the humidity sensor disconnected. Each ran perfectly, so I'm thinking it must be that sensor?

 

[Dan O.]

Could that cause the system to start and stop?

The sensor should have nothing to do with the motor's movements. I also wouldn't expect it to even be involved in just a regular timed setting. (I assume that's what you're testing it on?) I don't see how the sensor could be responsible. It's kind of expensive too:

LINK > KBMS1454RSS0 Sensor # W10871220


I might try it with the motor disconnected from the circuit for a short period to see if the control acted the same.

Dan O.

 

[alastair1008]

I've got the same problem as the OP, with the same model and the humidity sensor also reading about 3.1k, did replacing the sensor fix the issue?

for me it still cuts off with the sensor disconnected so I'm concerned it might be an issue with some of the components on the board that deal with the sensor. When probing the pin on the microcontroller that seems to be associated with the humidity sensor i get some strange behavior.