Microwave oven -- Whirlpool MD365WH

This means the door interlock switches are failing.

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1PW

Hi IPW and thank you for your reply.

Please let me elaborate a bit on the behavior during the hot air function.

If I open the door during the hot air function the oven runs for about

3-5 sec before it stops, therefore I belive that heating, fans and the rotating plate is relay controlled by the microprocessor and that the interlocks only shuts down the magnetron (I´m not sure though).

Or is it possible that glitching interlocks can cause all these kind of erratic behavior, possibly confusing the microprocessor?

Kind regards, Marcus Lindahl

1PW wrote:

One would believe that the door interlocks function for all modes. However your observation & theory may be quite accurate. Truthfully though I don't know what normal operation is for your particular model.

The URL I sent you, in the previous post, might be helpful. Erratic behavior may sometimes be traced to intermittent grounds or power supplies going bad.

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1PW

I've seen this in other electronics (not microwave ovens).

You said the problems were intermittent. Is the oven more likely to work correctly when it's cold (that is, it hasn't been used for several hours), or do the problems occur at any time, whether or not the oven has been used?

If the oven usually works correctly when "cold", I would start looking at the power supply, especially the capacitors.

Hi!

I've never seen a properly functioning microwave oven where *any* part of the oven continued to operate if the door was open. It seems to me like letting any part of the oven continue to operate might alarm the end user at the very least.

However, I have seen a Sharp oven with a bad door switch that would start its fan (and maybe the turntable as well) whenever the door was opened and the oven was off. Replacing the one bad switch cured the problem entirely, and the oven works fine to this day.

This is something that you should examine. However, please do consider the fact that a microwave oven is easily the most dangerous appliance you have in your house due to the high voltage. With its power cord unplugged and the capacitor discharged, the oven will be inert...unless of course, you drop it on your foot.

If that fails, I'd make sure that the sensors used in the cooking process are clean, and I'd also consider cleaning the control board. Many ovens don't protect it from food vapors and grease. If that stuff got on the board, it could be shorting out and messing up all kinds of signals going to the controller.

I don't think it would harm anything to simply wash the control board in warm soapy water as long as you let it have a day or two in a sunny window to dry out. Rotate it periodically so that a different side faces the window.

William

I don't know that particular model, but sometimes the flexible ribbon cable that connects the keypad to the main controller printed circuit board has intermittent contacts. Have you checked this by reseating the cable?

Hi,

Thank you for your answer.

On this model the cable that connects the powersupply control circuit board is directly soldered on each board, there are no connectors.

I have tested with cooling spray and found that when I cool down the microprocessor the oven starts to behave erratically. So probably there is a problem with that one. The microprocessor is mounted directly under the VFD, probably the heat generated by the display have killed the proecssor after its 10 years in operation.

Kind regards, Marcus Lindahl

I have found that when you cool down microprocessors like that, they do tend to fail, sometimes permanently.. I don't think I would put too much stock in that observation. Has anyone experienced this??

Gus.

Hi Gus,

I have actually never killed any component using cooling spray. However, I do think that I can put this particular microprocessor on the killing list. The microwave oven now automatically starts up as soon as a put the coord in the wall outlet.

My theory is that the microprocessor was failing, and that my cooling adventures made it fail completely.

I seams possible to buy a whole new control board as a spare part, but it costs ~200 dollar, which is more than I am willing to spend on a microwave almost 10 years.

Kind regards, Marcus Lindahl

Gus wrote:

You're probably correct about the uP, but I wouldn't rule out the possibility of a power supply problem.

Hi!

I've got my doubts. Thermal shock is a real possibility and could have happened here.

I'm sure it is. However, for that same $200, you could buy a very nice microwave oven. And that's the unfortunate thing.

You might consider saving some of the parts from your current oven, as some of them are useful, could make good spares or are suitably dangerous (!!!) depending upon how you look at things.

William

I would like to thank everybody for hints and ideas about what´s wrong with my microwave oven, but as the microprocessor now has died on me I will not put any more efforts in repairing it.

Thanks again for your support!

Kind regards, Marcus Lindahl

William R. Walsh wrote: