Oven displaying wrong temp...

[lj_robins]

Hi,

I have a Maytag Gemini stove model # MER6872BAW, about two weeks ago
everyone started noticing that nothing was getting fully cooked in the
upper oven. We use the upper oven a lot so I figured it was either the
sensor or the element.

I stuck a fireplace thermometer in the upper oven just to make sure
everyone wasn't going crazy, the temp on the oven's digital display said
400 degrees, the fireplace thermometer said 310. I stuck the thermometer
in the lower oven, the display and the thermometer both said 400 degrees.

Figuring that it was the sensor I replaced it, the upper oven still
acted the same. I was able to find a schematic for the oven on
Sears.com, the sensor goes straight back to a connector on the circuit
board inside the control panel.

The new and old sensors both read a little over 1000 ohms, the sensor
connectors for both lower and upper ovens are both reading 5.15 volts
DC. My only guess on this is that there is something wrong with the
circuit board. I looked it over all the parts look fine, no burnt
resistors, none of the capacitors are bulged at the top, no popped
transistors.

The oven did give me a code F9-3 while I was working on it which decodes
to: "Check for obstruction in door lock mechanism" (there is nothing in
the mechanism). Oddly enough six months after we had this stove it gave
that code with no warning at all, it gave another code too but I do not
remember that is was. A month later it did it again, then no problems
with it at all for three years until too weeks ago.

Anyone have any suggestions on what might be wrong?

 

[[email protected]]

Well I don't know much about that stove, but I do have some experience
with transducers (sensors). There's probably nothing wrong with the
transducer itself. The transducer would have to run onto the stoves
circuit board and into an a/d (analog-to-digital) converter and the
resulting hex value would have to be read by a microprocessor. The hex
value is meaningless to the processor by itself so it needs something
to reference it to to give you the resulting temperature (this is all
assuming the stove displays the temperature on a digital display). What
I'm getting at is ........bad calibration/incorrect programming on the
part of the manufacturer. Now don't take my word as gold but you might
want to look into that possibility.

 

[Bill Jeffrey]

Can you exchange the sensors, or exchange the connections, to localize
the fasult to sensor or not-sensor?

Bill

 

[T Shadow]

Hi,

I have a Maytag Gemini stove model # MER6872BAW, about two weeks ago
everyone started noticing that nothing was getting fully cooked in the
upper oven. We use the upper oven a lot so I figured it was either the
sensor or the element.

I stuck a fireplace thermometer in the upper oven just to make sure
everyone wasn't going crazy, the temp on the oven's digital display said
400 degrees, the fireplace thermometer said 310. I stuck the thermometer
in the lower oven, the display and the thermometer both said 400 degrees.

Figuring that it was the sensor I replaced it, the upper oven still
acted the same. I was able to find a schematic for the oven on
Sears.com, the sensor goes straight back to a connector on the circuit
board inside the control panel.

The new and old sensors both read a little over 1000 ohms, the sensor
connectors for both lower and upper ovens are both reading 5.15 volts
DC. My only guess on this is that there is something wrong with the
circuit board. I looked it over all the parts look fine, no burnt
resistors, none of the capacitors are bulged at the top, no popped
transistors.

The oven did give me a code F9-3 while I was working on it which decodes
to: "Check for obstruction in door lock mechanism" (there is nothing in
the mechanism). Oddly enough six months after we had this stove it gave
that code with no warning at all, it gave another code too but I do not
remember that is was. A month later it did it again, then no problems
with it at all for three years until too weeks ago.

Anyone have any suggestions on what might be wrong?

Control on our oven can be calibrated/offset. Could it have been changed?
Just brining it up because you don't mention it.

 

[James Sweet]

Hi,

I have a Maytag Gemini stove model # MER6872BAW, about two weeks ago
everyone started noticing that nothing was getting fully cooked in the
upper oven. We use the upper oven a lot so I figured it was either the
sensor or the element.

I stuck a fireplace thermometer in the upper oven just to make sure
everyone wasn't going crazy, the temp on the oven's digital display said
400 degrees, the fireplace thermometer said 310. I stuck the thermometer
in the lower oven, the display and the thermometer both said 400 degrees.

Figuring that it was the sensor I replaced it, the upper oven still
acted the same. I was able to find a schematic for the oven on
Sears.com, the sensor goes straight back to a connector on the circuit
board inside the control panel.

The new and old sensors both read a little over 1000 ohms, the sensor
connectors for both lower and upper ovens are both reading 5.15 volts
DC. My only guess on this is that there is something wrong with the
circuit board. I looked it over all the parts look fine, no burnt
resistors, none of the capacitors are bulged at the top, no popped
transistors.

The oven did give me a code F9-3 while I was working on it which decodes
to: "Check for obstruction in door lock mechanism" (there is nothing in
the mechanism). Oddly enough six months after we had this stove it gave
that code with no warning at all, it gave another code too but I do not
remember that is was. A month later it did it again, then no problems
with it at all for three years until too weeks ago.

Anyone have any suggestions on what might be wrong?

I doubt that code has anything to do with the problem.

Does the control board have any analog conditioning after the
temperature probe? If so are there two identical circuits? If you can
compare readings right at the pin into the microcontroller you'd know if
the problem was before that or within it. You might simply have a bad
ADC in the microcontroller in which case you're pretty much SOL unless
you feel like writing your own code from scratch to program a replacement.

 

[lj_robins]

Hi,

I have a Maytag Gemini stove model # MER6872BAW, about two weeks ago
everyone started noticing that nothing was getting fully cooked in the
upper oven. We use the upper oven a lot so I figured it was either the
sensor or the element.

I stuck a fireplace thermometer in the upper oven just to make sure
everyone wasn't going crazy, the temp on the oven's digital display said
400 degrees, the fireplace thermometer said 310. I stuck the thermometer
in the lower oven, the display and the thermometer both said 400 degrees.

Figuring that it was the sensor I replaced it, the upper oven still
acted the same. I was able to find a schematic for the oven on
Sears.com, the sensor goes straight back to a connector on the circuit
board inside the control panel.

The new and old sensors both read a little over 1000 ohms, the sensor
connectors for both lower and upper ovens are both reading 5.15 volts
DC. My only guess on this is that there is something wrong with the
circuit board. I looked it over all the parts look fine, no burnt
resistors, none of the capacitors are bulged at the top, no popped
transistors.

The oven did give me a code F9-3 while I was working on it which decodes
to: "Check for obstruction in door lock mechanism" (there is nothing in
the mechanism). Oddly enough six months after we had this stove it gave
that code with no warning at all, it gave another code too but I do not
remember that is was. A month later it did it again, then no problems
with it at all for three years until too weeks ago.

Anyone have any suggestions on what might be wrong?

Thank you for all the replies, it turned out to be a bad solder joint on
the controller board, oven works fine now.


-Landon

 

[t- 4 technician]

Damn! the old bad solder joints, they'll get you every time!