• ** 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

KHMS2050SSS1 - every time I start the microwave, it runs successfully for a few seconds, then immediately stops and quickly resets

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Model Number
KHMS2050SSS1
Brand
KitchenAid
Age
6-10 years
Hello, All:

Well, it seems I've created a new problem with this PITA OTR Kitchenaid microwave. I made some recent comments on this thread:

about replacing the control panel and User Interface Board (UIB), because the microwave control was operating by itself. I thought I'd start a new thread, since I have a new problem.

So, here is where I am now:
  • I had previously installed a new keypad (control panel). However, this didn't resolve the issue, so I then installed a new UIB, which again, didn't resolve the issue.
  • I obtained an "exchange" for the keypad, and installed it yesterday.
  • The good news is that the issue of activating cooking programs by itself seems to be resolved. When powered on, the keypad does NOT do random beeps and program changes.
Now, the bad news-------while the control seems to work perfectly now, every time I start the microwave, it runs successfully for a few seconds, then immediately stops and quickly resets. Sometimes, it continues running for a few seconds again before resetting again. Other times, it just stops and resets to the point that the time and all settings are cleared as if the microwave had been unplugged. When the microwave works, the turntable turns and it heats water, so this still seems to somehow be a problem with the controls. Unfortunately, it shows NO error codes, so I have nothing to point in a direction.

So, I seem to have introduced a new and more complex problem. I've checked and double-checked all of the wiring to make sure I don't have any pinched, disconnected or otherwise obvious defects, to no avail.

Up until now, I've actually been able to remove the door as described in the thread above, and work on the microwave installed over the stove. However, it seems that I may now need to take the microwave down and put it on my bench, where I can pull it apart and do some serious troubleshooting.

I don't think I've ever been so frustrated with a repair. I've thrown several hundred dollars at this, so I'd hate to call it quits, but I'm seriously wondering if it's time to get a new microwave, although because of the unusual size configuration of this unit, that approach will cause me to make some tile and cabinetry changes, so it's not without it's own headache.

Enough of my ranting ----- does anyone have any clues to narrow this down a bit more for me?

Thanks very much in advance!
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
UPDATE-----I was able to remove the microwave today, open it up, and spend some quality diagnostic time with it.

Here's what I've found so far:
  • The control panel seems to be working just fine now. No "ghost" beeps or program changes, and the keypad responds perfectly to the keypad test indicated in the tech sheet, so my recent replacement of the keypad and User Interface Board appears to be a success.
  • The microwave continues to run for a few seconds, abruptly stop, then restart or reset, often as if the unit has been unplugged and then plugged in again. When it works for a few seconds, it's heating water, so the magnetron is clearly working.
  • When I disconnect the inverter and/or magnetron from power, everything else on the microwave works as expected and runs without interruption.
  • Using the tech sheet and an ohmmeter, I've run simple tests on the magnetron and AC line filter with nothing abnormal. I've also inspected the relay control board, the relay board, and the inverter, as indicated in the tech sheet, again with nothing appearing out of the ordinary.
So, I'm thinking that the current problem is not directly related to the control problem that I had previously. My suspicion is the problem is either the inverter or magnetron, since everything else on the microwave works fine when these have been disconnected from power. However, I'm also a bit suspicious of the relay control board, since that failure is listed as one of the common causes for "microwave stops after a few seconds", it has a signal wire loom that is attached to the inverter, and there isn't a way to test this relay control board.

So, which do you think is the more likely failed component? Or have I missed something?

Thanks again!
 

rickgburton

Appliance Tech - Moderator
Staff member
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Messages
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Location
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See if the microwave will operate correctly with the CN702 connector disconnected from the inverter board.
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Rick:

Thanks for the reply --- I've tested it with CN702 disconnected from the inverter, and the microwave runs fine without resetting, however, as you would expect, no heating occurs. This is the same behavior as when I disconnected the power to the magnetron and inverter----all of the controls work, but no heating occurs.

So, does this point to the relay control board (to which the cable from CN702 connects) or the inverter board? I've got both on order, so I hope it's one or the other.

Thanks again for your response!

Rob
 

rickgburton

Appliance Tech - Moderator
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By disconnecting the CN702 connector you've split the system into two parts, the low side and the high side. Since the microwave runs fine with the connector disconnected that eliminates everything on the low side including the relay board. The mag tube usually works or it doesn't. Here's the part you need:
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Thanks, Rick, that inverter board is exactly what I ordered yesterday. I should get it in a few days, and I'll report back once I have it installed.

Thanks again for the help and the benefit of your experience!
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Okay, big disappointment ----- first, I installed the new inverter, but it made no difference-----the microwave will start, then a couple of seconds after the magnetron kicks in, it will lose power and reset. No error codes, and the issue is fully repeatable. Sometimes, it will run up to 10 seconds or so before resetting, and other times, it will only run a few seconds, but when it resets, it's always after the magnetron kicks in. I then installed the new relay control board, again with no improvement. The only significant parts I have NOT replaced are the magnetron (seems to work and heat when it works), the electronic control board (WP8206493) and the noise filter board (WPW10286198).

So, at this point, I've replaced the keypad, the User Interface Board, the inverter, and the relay control board. The original problem with "ghost" keypad presses is resolved. This current problem started after I had to replace the keypad a second time because the first replacement was defective. I'm also wondering if the UIB I received may be defective or if I now have a problem with either the remaining electronic control board or noise filter board. Ideally, I'd like to isolate the inverter/magnetron and see if it works with everything else disconnected, but disconnecting CN702 from the inverter lets all of the controls work, but kills the inverter circuit. Also, if I remove power from the inverter and/or magnetron, the controls work fine without resetting. The schematic is not detailed enough to show how to jumper anything to totally isolate the controls from the inverter/magnetron so that I can test only the inverter/magnetron circuit.

I'm very frustrated with this, since I feel like I'm throwing parts at it, but not really making progress. However, I refuse to let it get the best of me. I have uploaded a video of what is happening, so I hope that is better than my description.

Any additional suggestions?

Thanks very much for any clues you can give me.
 

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rickgburton

Appliance Tech - Moderator
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I'm going to look at the schematic and see if I can figure out any test points. Stand by.
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Thanks for the response, Rick! Any ideas are much appreciated. In the meantime, I'm probably going to order a replacement UIB board. I'm still trying to figure out how to isolate the mag/inverter from the controls, so that I can just run the mag by itself to see if it still kills the machine.

In a couple of posts up, what did you mean by disconnect the "tube"?

Thanks again for all of your help and suggestions!
 

robhouston

Premium Member
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Messages
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Location
Chester, NJ
Rick, I think I figured out that by "tube", you mean the magnetron. Yes, I've disconnected the magnetron, and the microwave runs fine (all of the controls, timer, etc work) without constantly resetting. Of course, with the magnetron disconnected, there is no heating. Once I reconnect the magnetron, it goes back to resetting every few seconds, and in the few seconds the machine runs, it heats water.

This has made me think that something in the magnetron circuit is causing the machine to reset, and I hoped that was the inverter. The only other significant components in the magnetron circuit are the filter board and magnetron itself. Is it possible that the magnetron could do something like this? I would have thought that the fuse would blow if it's pulling too much current, but something is causing the machine to reset.

I'm still scratching my head........
 

rickgburton

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The mag tube is the problem. Remember I said you split the system into two sides and we determined the issue was on the high side. The high side on your machine consists of an inverter and mag tube. Usually the tube either works or it doesn't so when you said yours was heating I assumed it was good. I guess I was wrong...lol Measure the resistance of the tube. It should be less than 1Ω. Then check from each terminal to the tube body.
If you got the inverter from the link I gave you, you can return it for a full refund less shipping. Replace the tube and you should be back in business.
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
Thanks, Rick!

Just to clarify, when I split the system by disconnecting CN702 from the inverter, that removed power from the inverter/magnetron side. When running the machine with the system split, the controls, fan, lights, etc all worked normally with no resetting. Since power was removed from the inverter/magnetron, there was no heating of water in the oven, as expected.

So, are you saying that it means that the problem is somewhere in the inverter/magnetron side? Since those are the only two significant compenents on that side, it has to be one or the other?

I'm still not clear why the whole oven resets when the inverter/magnetron is powered up.

Anyway, I'll order a magnetron. I'm going to hang onto the inverter until this is resolved or I give up, just in case it needs replacing after all.

Thanks again, and I'll report back in a few days.
 

robhouston

Premium Member
Joined
Feb 24, 2008
Messages
18
Location
Chester, NJ
The magnetron tests fine with an ohmmeter. I've got a new one and a replacement User Interface Board on the way, so I'll report back after I get the parts installed.

Wish me luck........
 
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