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Microwave oven -- Whirlpool MD365WH

M

Marcus Lindahl

Jan 1, 1970
0
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)
 
1

1PW

Jan 1, 1970
0
Marcus said:
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/>
 
M

Marcus Lindahl

Jan 1, 1970
0
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
 
1

1PW

Jan 1, 1970
0
Marcus said:
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.
 
W

William Sommerwerck

Jan 1, 1970
0
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.
 
M

Marcus Lindahl

Jan 1, 1970
0
hr(bob) [email protected] said:
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
 
M

Marcus Lindahl

Jan 1, 1970
0
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
 
W

William Sommerwerck

Jan 1, 1970
0
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.
 
M

Marcus Lindahl

Jan 1, 1970
0
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
 
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