Jenn-Air Broiler Fan Runs Constantly

[kc8adu]

Re: Jenn-Air Broiler Fan Runs Constantly

u2 eeprom corrupt?
anyone dump a working board and make a new eeprom for a sick one?

[Longbow]

Re: Jenn-Air Broiler Fan Runs Constantly

I hope someone out there can dump a working EEPROM to file. That way we can see if that part is the culprit. The appliance sheet in the photo is correct. But, it is a wiring diagram, not a schematic. There is no schematic on the board except in the bowels of the RobertShaw corporation. Appliance manufacturers don't expect component-level troubleshooting. Couple of other comments: I did study the detailed tech sheet on the microprocessor. It is an early micro that is definitely not a hot item on things like controller boards these days.. One thing I noticed was that there is a special programming language for chips of this series. I've never heard of that chip-level language, but that's not my line of work.

Someone mentioned further back in the thread that the micro is mask programmed and thus could never lose its memory. Well, maybe he works for the manufacturer of the chip, but the tech sheet is full of instructions on how to program the IC, what commands do what, i/o pin definitions, etc. And, the serial interface is definitely not one I have seen. Its not a memory chip, but it does have a large chunk of memory for storing the program. So it now looks like they selected that chip for the on-board memory capacity too.

I've recently become aware that some board materials in older equipment can indeed absorb moisture, or undergo some kind of chemical reaction which turns the board into a chunk of conductive plastic. I came across one board like that. I could measure resistance in the megohm region between any 2 places on the board just by jabbing my probes into it. Cool. However the new oven controller board is made of the same yellow junk that old one is.

One final thing. Some people are insisting that we are dealing with a faulty thermocouple or temp sensitive resistor. This is not correct. The problem is definately fixed by replacing the controller board, which is on the back of the oven. The purpose of the broiler fan (misleading) is to cool the space directly above the broiler element. That space contains the timer pcb. Yes, the fan cools the timer board when the broiler element is ON, runs for a minute or two after broil is OFF, then stops. There is no temperature sensor in the timer pcb area. The control board is nowhere near the broiler area, so the whole thermocouple thing is on the wrong track. But, a new controller board fixes the problem. That's the way it is.

[gozzard36]

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.

Just a point of clarification: The RTD does indeed act as a variable resistor. A thermocouple is a device of two differing metals which creates small voltage differences as temperatures change. These thermocouples also require a reference junction whose temperature is known to be able to extrapolate the voltages with reference to the junction.

[HmeOwnr]

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

Hi Longbow,
Can you tell me what supplier has the controller board available at $200? Thanks

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

[HmeOwnr]

Re: Jenn-Air Broiler Fan Runs Constantly

I have a Jenn-Air single oven MODEL SVE47500 and the problem is that when the oven temp goes on then the exhaust fan runs thus cooling the box so no cooking takes place... look like it needs a new Electronic Clock Control Board. Where can the best price be found for the Oven Control Board p/n WP71001799?