Jenn-Air Broiler Fan Runs Constantly

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

After thinking about the cooling fan symptom for some time, I think it is worth noting that a likely explanation may have to do with the EEPROM. It is up to the designers, but many generic uPC store the program and user settings in EEPROM. Many articles report how easily EEPROM data is corrupted by timing errors, incorrect power-up and power-down circuit design and so on. Not all of the data is instantly trashed, which would explain how only a few functions might be affected. Each time the stove goes down in a power outage (as an example) the integrity of the data may be compromised.

Anyway, this explanation seems the most likely to me. Since many JenAire owners deal with the fan runs all the time (along with erratic error codes and other mystery behavior), there it is - my guess. The only way to test this theory would be to have a known faulty board and replace the EEPROM with one from a known good board. Since the IC is an 8 pin generic part, good data can easily be read out and stored in a file...and used to re-write a new part.

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

Thanks for your experiences on this dr. hook. The flex-cable on the timer board isn't all that great and it is easy to push it in off center. I've heard a number of reports of the same symptom happening after the clock display has been fixed. Assuming the connector at the timer board is ok, the "cooling fan runs all the time" symptom is unrelated and so far all the details are still a mystery. The only thing that is known is that the main controller board fixes that problem. Some people just disconnect the cooling fan and leave it like that. But the fan does keep the timer board from roasting. I still don't like the idea of combining microprocessors and ovens, but that's progress for you.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

Thanks for the note.
I'm sure it will help someone with one of those ovens in the future.
.

[drhook]

Re: Jenn-Air Broiler Fan Runs Constantly

Hey everybody,
First I'd like to give thanks for the other post on the control board (clock) fix.

After fixing the control board for 23 cents plus shipping everything worked fine. Then a day later the cooling fan and light came on and stayed on. I found the problem to be a short caused by the factory fold in the ribbon cable connected to the same board.

Quick test to verify:
turn off the power at the breaker
drop the front panel
remove screws that hold board and retainer in place
turn on the power
tilt the board upward and back
at some point the fan should go off (you may need to bend the cable straight a little)

Quick fix:
cut a strip of packing tape about 4" long and slide it behind the ribbon and around the front so that the ribbon curls into the connector on the board like it should.

I don't know how long the fix works for but I'll be keeping my eye on it.

[b700029]

Re: Jenn-Air Broiler Fan Runs Constantly

If you really want to figure it out, trace the PCB and make a schematic.

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

Did you check the components between the microcontroller and the temperature sensor?

Remember, the oven temperature is controlled normally by the oven temp sensor. That eliminates the temp sensor and the circuit that controls the oven temp. On the other hand, the circuit that decides when to turn the fan on and off also uses the same sensor, but different logic, presumably located on the daughter board, a double sided board with SMD components. Checking components? Of course. It would be an easy problem if there were a simple smoked part. It could very well be a board leakage problem. Too bad that daughter board isn't available separately.

As above, one side of the fan relay coil is controlled directly by one uPC output pin acting through a relay driver. The other end of the coil is controlled by a massive amount of on-board logic elements, transistors, ic's, etc. I can't do much more without a schematic.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

Don't know if I believe that part. Why there would be moisture on the back of the oven?

Condensation as it cools down after use.
Would only be a problem in high humidity.
.
Generators of any significant size actually have heaters that come on when they are shut down for that exact reason.
.

[lti]

Re: Jenn-Air Broiler Fan Runs Constantly

Did you check the components between the microcontroller and the temperature sensor?

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

I've done a lot of troubleshooting on this problem, which has been reported almost as often as the JennAir dim clock symptom. Although I have not discovered exactly what the problem is, I'd like to summarize the information that is known, so that others might be able to take it farther than I could.

Photos show the original (faulty) board that came with the range (1995). Here is what is known:
1) Correct fan operation is to come on when the oven is set to broil or shortly after initial warmup. The fan will then run until the oven temp again reaches about 200 degrees, then shut off. Faulty operation is for the fan to keep running for hours after the oven is cool, or forever.

2) The problem (as yet unknown) is on the main controller board and is fixed by replacing the board (confirmed) - costs over $200.00.

3) The controller board is absolutely not sensitive to freezing or heating - the only outside sensor used is the oven temp sensor inside the oven. Freezing the temp sensor with freeze spray will stop the fan. Those results suggest that one or more parts have changed value or failed permanently.

4) DC operating voltages are produced on the controller board (13 volts and 6 volts) by linear means and crude zener diode regulation. There are only 2 electrolytic filters on the board (both replaced).

5) The fan is turned on by the uPC which sends a high signal to a relay drive IC (shown) that produces and active low on one side of the fan relay coil. The other side of the coil is controlled by a switched +12 volts, glue logic and other unfathomable logic processes which ultimately are controlled by the uPC.

6) The main uPC "fan on" output (pin 26) and relay drive work normally. The mystery lies in the logic (and lots of it) connected to the other end of the relay coil. Personally, I can't understand why the uPC can't do all the work and just issue one output, but I really have no experience in heat control designs.

7) All indications are that the problem is on the daughter board shown in the photos. Lines to the daughter board go back and forth to the oven thermostat plug (J10) and to the uPC, then back and forth to a calibrating resistor (J9) on the main board. The calibration resistor at J9 is not used on the new controller board and that is the only discernible difference between the two boards as far as I can tell.

8) The daughter board contains 2 ic's and a handful of transistors - one LM339 quad comparator and one LM224 quad op amp (both ic's were replaced). No obviously faulty transistors or resistors. There are 2 SMD caps on the rear (.15 ufd). Found one leaky and replaced with no difference.

Why there needs to be 4 comparators and 4 op amps I have no idea, especially with a uPC and an EEprom. I imagine that at least one function is a precision reference voltage. Another may be a current sensing circuit. I think the decision to run the fan takes place on this board, then is sent to the uPC, but this is not a certainty. There are a handful of transistors on the main board as well. None of them show any signs of being faulty on either board.

The new board comes with a metal shield that fits between the controller and the back of the oven. The sheet that comes with the new controller says that the shield "is to block the path of any potential moisture from contacting the back of the relay (controller) board." Don't know if I believe that part. Why there would be moisture on the back of the oven? It makes a lot more sense that the shield would deflect or disperse some of the oven heat.

That's all I know. The new controller fixes the problem. I hope someone can take this information and find something I missed; at least its a start. There's probably a 10 cent part that has changed value. I don't think that the uPC just forgot a few lines of code; all other functions on the old board, including keeping the oven at the proper temperature, work normally.

Longbow

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

I saw some complaints of a conductor in a ribbon cable breaking due to being pinched when installed.
.
Not sure what to make of that [if it applies] because I haven't seen the whole thing together.
- Might check continuity on any ribbon cables involved..
.

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

That's the one! Appliance repair forums are full of references to the problem and to the solution (new board). The new board comes with a metal heat shield that fits between the board and the oven. All that information leads to 2 places. 1) there is a temp. sensing part on the board that is faulty. I don't go for this explanation because the board is on the back of the oven and without an external sensor (like the oven temp sensor), it can't know what the oven temp really is. 2) A part on the board has changed value or become leaky, or a trace opens up when the board is warm. I go for this one big time. The actual oven temp sensor works fine keeping the oven at the correct temp, BTW. As I said. Since I am thinking about the problem I'm getting out my hair dryer and freeze mist to see if I can force something to happen.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

This it?
http://www.repairclinic.com/PartDeta...200&locID=3124

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

Yes but at most appliance parts places if you don't have a model number you can't look ANYTHING up.
Just looking for a pic of the controller at this point.

You said the relay works so if cold spray does nothing that suggests the thermostat contacts have failed open or shut, or perhaps an open conductor.
.

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

The actual Jenn-Air model I have is the SVE-47500. But, the controller board along with all its quirks is used in a number of Jenn-Air oven models, and many more of the generic Jenn-Air ovens as well - (different manufacturer names). symptoms are the same in all of them. The controller boards are made by RobertShaw and schematics are proprietary.

So all the foregoing troubleshooting theory is sound enough. One might think that since the trouble is related to the temperature of the oven, and furthermore that the problem happens reliably each and every time, that some freeze spray would instantly bring us to the culprit. No luck with that method. But we do know that replacing the main controller board fixes the problem. I've never heard of a relay that turns itself on an off. A leaky relay driver transistor is certainly a possibility, but again, a blast of freeze spray would instantly show that problem. I'm leaning towards a pc trace that opens up when the board gets warm. Think I'll have another close look at this aspect. Will post some photos when I remove the board.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

Trolling aimlessly [BECAUSE I DON'T KNOW THE MODEL NUMBER] though a Jenn-air oven parts catalog suggests a mechanical thermostat is typical.
.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

i know (other than my terminology snafu), but i'd imagine there is more than just a transistor involved. maybe not though...

Well, yeah. The transistor has to be biased somehow.

Might not even be a transistor though.
A mechanical thermostat with a thermocouple could be switching the coil.
[That's what my fridge has. A mechanical thermostat sends [or removes] voltage from a pin on an IC. - I REALLY wish I didn't know because that would mean I never had to fix it..]

HEY OP!
A model number might help...
.

[ratdude747]

Re: Jenn-Air Broiler Fan Runs Constantly

i know (other than my terminology snafu), but i'd imagine there is more than just a transistor involved. maybe not though...

some ovens have real time temp feedback... to the OP, if your oven supports it, are the temp feedback values accurate? if you had some way to test the temp inside, then assuming both systems (fan control and temp feedback) are using the same thermocouple, then you could rule out a bad thermocouple based on your readings.

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

A Thermo Sensor is a Thermocouple. Also called an RTD.
It's a variable resistor.
Unless a cap is shorted it's not going to change much.
A relay would be used because it's old tech and switching AC to the fan.
The Thermocouple would switch a transistor that powers/de-energizes the coil in the relay which sends power to the fan.
.
Most likely suspects are the thermocouple and the relay (reported working) but it could be the transistor.

[ratdude747]

Re: Jenn-Air Broiler Fan Runs Constantly

since it sounds highly electronic (not just basic thermocouple to relay), i would would look at the themo sensor (blue or green sensor-small) and any capacitor on the circuit. replace the electrolytic caps for sure.

something in the sensor circuit is funky... sounds like its acting like a capacitor (once it starts it takes forever to stop).

one other possibility is something nearby is heating up and taking a while to cool down and at the same time the thermo sensor is out of calibration (bad sensor or other component in circuit.

a schematic would help a lot. somebody know of one?

[PCBONEZ]

Re: Jenn-Air Broiler Fan Runs Constantly

There is probably a thermocouple somewhere that trips the relay.
It or a related component has shifted value due to age.