Hi,

I have a Whirlpool MD365WH microwave oven. The problem is that the
automatic cooking functions is working erratically.

If I want to auto-defrost something the display reads out "Sense" and
after about one minute, when the program ends, the food is still frozen.
But sometimes it work perfectly, and sometimes as described above.

The hot air function is sometimes also working in mysterious ways. If I
open the door during cooking, the oven keeps running, but not always. I
guess the correct behavior should be to immidiately shut off when the
door is opened.

Sometimes the controlpanel does not respond when I press the buttons.

As I belive the problem stems from a faulty control panel, and I have
checked and done some resoldering at the controlpanel circuit board, but
unfortunately it had no effect.

Does someone here have any experience troubleshooting the electronics
(or perhapts schematics) in said microwave oven?

Kind regards, Marcus Lindahl (Sweden)

Marcus Lindahl wrote:
Hi,

I have a Whirlpool MD365WH microwave oven. The problem is that the
automatic cooking functions are working erratically.

If I want to auto-defrost something, the display reads out "Sense" and
after about one minute, when the program ends, the food is still frozen.
But sometimes it works perfectly, and sometimes as described above.

The hot air function is sometimes also works in mysterious ways. If I
open the door during cooking, the oven keeps running, but not always. I
guess the correct behavior should be to immediately shut off when the
door is opened.

This means the door interlock switches are failing.

Sometimes the control panel does not respond when I press the buttons.

As I believe the problem stems from a faulty control panel, and I have
checked and done some resoldering at the control panel circuit board, but
unfortunately it had no effect.

Does someone here have any experience troubleshooting the electronics
(or perhaps schematics) in said microwave oven?

Kind regards, Marcus Lindahl (Sweden)

http://www.repairfaq.org/REPAIR/

--
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:
Marcus Lindahl wrote:
Hi,

I have a Whirlpool MD365WH microwave oven. The problem is that the
automatic cooking functions are working erratically.

If I want to auto-defrost something, the display reads out "Sense" and
after about one minute, when the program ends, the food is still frozen.
But sometimes it works perfectly, and sometimes as described above.

The hot air function is sometimes also works in mysterious ways. If I
open the door during cooking, the oven keeps running, but not always. I
guess the correct behavior should be to immediately shut off when the
door is opened.

This means the door interlock switches are failing.

Sometimes the control panel does not respond when I press the buttons.

As I believe the problem stems from a faulty control panel, and I have
checked and done some resoldering at the control panel circuit board, but
unfortunately it had no effect.

Does someone here have any experience troubleshooting the electronics
(or perhaps schematics) in said microwave oven?

Kind regards, Marcus Lindahl (Sweden)

http://www.repairfaq.org/REPAIR/

Marcus Lindahl wrote:
Hi 1PW 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 believe 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).

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.

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

Kind regards, Marcus Lindahl

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.

--
1PW

Erratic behavior may sometimes be traced to intermittent
grounds or power supplies going bad.

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!

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).

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.

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

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

On Oct 8, 8:41*am, "William R. Walsh" wrote:
Hi!

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).

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.

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

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?

hr(bob) wrote:
On Oct 8, 8:41 am, "William R. Walsh" wrote:
Hi!

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).
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.

Or is it possible that glitching interlocks can cause all these
kind of erratic behavior, possibly confusing the microprocessor?
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 tested with cooling spray and found that when I cool down the
microprocessor the oven starts to behave erratically.

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:
I have tested with cooling spray and found that when I cool down the
microprocessor the oven starts to behave erratically.

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.

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 cord in the wall outlet.

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

Hi!

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

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

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.

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:
Hi!

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

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

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.

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