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Repair and disassembly guides for Kenmore Microwaves.

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Microwave (Kenmore 66568682891) dead - fuse is OK and power @ plug

I've got the above Kenmoe microwave. Had it for years. Been running perfectly. Today after heating for about 15 minutes on an automatic setting, but magnetron was on pretty consistently for 15 minutes, it got to the end of the cylcle and just quit. No lights nothing. Breaker was not tripped, it has power at the wall receptacle. I opened it up enough to get at the fuse on the front behind the control panel and the fuse tested 0 ohms so it isn't the fuse. Control panel is totally dark. It's like it isn't even plugged in.

One more factoid. This morning I used it to warm up a roll (30 seconds at 30% power. When I hit start. It started up as usual, but at first I heard a slight clicking sound,,,,about 4 clicks and then the clicking stopped and it completed the task as directed. Never heard that sound before . It didn't make that clicking sound when the heavier task above was being done pretty consistently for 15 minuest or so probably on 80% power.

Other than being unplugged or having no power at the AC wall plug in, or the fuse being shot (open) what would cause a microwave to be stone cold dead

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Hi @jellynell

I can't find a wiring diagram or a service manual for your model but here's some general information that may help.

A lot of microwave ovens have a Low Voltage (LV) transformer on the control board (this IS the board for your model, click on the 3rd mini image to the left to see the LV transformer and the relays etc) (see part #6 Control parts diagram for location.

Here's an image of a typical wiring diagram that shows how the oven may be wired. This is NOT for your model but it is to show how if the power doesn't get to the LV transformer or if there's a problem on the control board then there's no power for the board to function i.e. dead

Update (04/10/23)

@jellynell

That switch you pointed to is not the problem unless there's a loose wire on it

Looking at the schematic you provided, (see image below) there is always power on pin 9 (live) and pin 12 (neutral) of the control board unless the cavity thermostat is operated or faulty, there's a wiring problem or a problem on the control board.

If you follow each of the wires on the diagram, back from the two pins you will see that they get to L1 and N without having to pass through a closed switch, "except" the cavity thermostat which is normally closed. The power is connected to other switches but only gets through when they're operated either by the door being closed (interlocks) or the temp thermostat operating

Block Image

(click on image)

Update (04/10/23)

@jellynell

If there's power on pin 9 but no Neutral on pin 12 no current will flow through the LV transformer. This is the power that is used to supply the control board.

The control board switches 120V AC power but the relays etc don't operate at that voltage. They all use a lower voltage that is supplied by the LV transformer on the board, as long as it has power being supplied to it that is ;-)

You may have to do point to point continuity testing along the Neutral path.

Did you test the power cord from the plug's Neutral prong to where the Neutral wire is terminated in the oven, you didn't say? If not try that first, if may be a faulty power cord. Try flexing the cable, especially near the plug and check if there's continuity on the Neutral wire or if it "comes and goes" as you flex. It may be fractured

With the power disconnected, (also see safety advice below) place one Ohmmeter probe on the Neutral prong of the power cord plug, and then use the other Ohmmeter probe to check for continuity on the path i.e. start at pin 12 on the control board - if no good, then on the white wire of the primary interlock switch, if no good then on one side of the cavity thermostat. If still no good try the other side (they're both white wires so there's one each side and you don't know where it comes from - switch or prong). If you get continuity on one side of the thermostat, but not the other it is faulty.

See link above for replacement part.

Be safety aware - discharge the HV capacitor before testing. It can store >5000V DC for months even if the power has been disconnected for this length of time. This amount of voltage can seriously injure you.

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I'm wondering if it's the "cavity thermostat" on the neutral wire, because I have continuity from the hot prong of the plug to pin 9 but there is no continuity between the neutral prong of the plug to pin 12. As I read the schematic (which I do NOT do well, I admit) the only place it could break continuity other than a broken wire, which I doubt, is at the cavity thermostat. And if the neutral is disconnected, everything is going to be dead, lights, display, everything. What are the chances?

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@jellynell

Which fan runs on high, the fan in the hood or the oven fan?

If it is the hood fan then there may be a problem with the thermostat in the oven as it has to be operated to provide the circuit for the hood fan to function. Did you wire the replacement back in correctly? Blue and white wires should be terminated together on one side if the thermostat and the two red wires on the other side.

Given that nothing else works have you inspected the control board for any damage? You said that there's AC to the oven (presumably on the control board), but have you checked if there LV power on the board?

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Well, you've already covered the basics so that's good. Most of the at fixable problems I've run into with microwave ovens have been tied directly to the door switches. There are usually three microswitches on the door that control whether power can be applied to the magnetron, etc. When those switches go out you can get all kinds of weird behavior with things turning on when they shouldn't or not turning on when they should.

So I'd suggest your next step should be to use an ohmmeter or continuity tester to check the operation of the switches as you open and close the door (with power disconnected, of course). The switches themselves are very common and easy to get; just make sure the voltage and current ratings of the replacements are equal to or higher than the ones you take out. They come in two flavors, normally open or NO, and normally closed or NC, so you'll need to get the right one for the particular switch you're replacing. You can always buy a combination switch that has both NO and NC connections; that one can be used to replace either type just by plugging the wires into the appropriate terminals.

Check out those switches and let us know what you find.

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I have checked out the switches and from what I can tell. They are OK.

Question is the "Temperature switch" (arrow points to it) just after the fuse supposed to be open? Mine is.

Block Image

Update (04/15/23)

Ok. Replaced the cavity thermostat and the thermostat just behind the control board, so now I have power to everything. They were both blown. I think the cavity thermostat on top of the cooking compartment blew (and it did blow) because there was a loose connector and it begain arching and heated up. Why the one behind the control board blew too, I don't know.

So now I have AC to the microwave, but when I plug it in the fan runs on high and other than that it's pretty unresponsive.

Control board itself blown? Probably time for a new microwave.

Comments welcome.

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That's hard to tell just from the schematics. Does the part itself have any markings on it so maybe we could look it up and figure out how it's supposed to work?

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Yes, there are four markings:

36Tx12

560186

F60-15C

S9846

I'll try looking them up too.

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@jellynell It may be testable; from what I can tell so far that 15C number indicates the switching temperature, which converts to about 59 degrees Fahrenheit here in the US. I'd imagine if you pop it in the fridge you should be able to see it switch when you take it out and let it warm up.

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@jellynell and @dadibrokeit isn't that switch for the fan cooling motor? those are normally open switches. Whirlpool uses a model F60-15C which is a resettable switch

okay, found one. This is a F60-15C model https://www.certified-parts.com/browse-p...

@jellynell just checked your MW number and the 665 is actually made by Whirlpool

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@oldturkey03 Makes sense; a lot of Kenmore appliances are made by Whirlpool.

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Final Update: SUCCESS! The item noted as the "Temperature Switch" (see the schematic posted above) is supposed to be OPEN! If I read the schematic more carefully, I'd have noticed that (and I warned you that I was a novice and not good at reading schematics). So I'd replaced it with an incorrect component that was closed in its normal state. When the microwave malfunctions and overheats that CLOSES that component, signalling an overheated state. Thus, that shuts down the whole microwave except for the fan which runs on high, presumacy to cool down the overheated microwave. When I put the original "thermostat" (the one behind the control panel) which I'd assumed was faulty because it was open, the microwave sprang back to life.

So, the final verdict: The only component which had truly failed was the "cavity thermostat" which is meant to be closed in its normal state and had blown not because the cavity (the cooking compartment) had become too hot but because the spade connectors were not really tight on it, and it began arching and overheated. It truly blew. See the photo.

So for now I'm back to running fine. Thanks for all the gret comments, and thanks too for dadibrokeit's knowledge which helped me immensely to figure this out, ("isn't that switch for the fan cooling motor? those are normally open switches....."). That comment made the lights go on for me and to the successful fix. Thanks

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Hi @jellynell,

I edited your answer earlier from dadibrokeit to oldturkey03 because if you read the comments in your answer from 6 days ago it was actually oldturkey03's comment where he suggested that "isn't that switch for the fan cooling motor? those are normally open switches....." and not dadibrokeit.

Credit where credit is due.

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jellynell wird auf ewig dankbar sein.
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