TheFixitGuy
Premium Member
- Model Number
- PT7550
- Brand
- GE
- Age
- 6-10 years
About 3 months ago, my GE Double Oven (PT7550 model) started displaying F34 error codes which would occur intermittently and without warning. These were initially a nuisance as I was able to cancel the error and the oven would continue to operate normally for a time, but as they increased in frequency it became a real problem as they would shut down the oven completely even while cooking. In researching the issue, the first problem I ran into is that no one seemed to have a clear idea of what the code actually meant. Answers from Internet "experts" were "shorted circuit upper sensor probe", "open circuit upper sensor probe", "meat probe problem", etc. with no real consistency. The result was that others having the issue would replace probes, boards, etc., often without a resolution. So I then decided to track down the GE service guide for the oven and was fortunate enough to find one online. I scanned through the code descriptions in the guide and discovered that - according to GE - for this oven, codes starting with F3 indicated an open oven sensor. I figured, "Great. I'll check the sensor see if it reads open." So I pulled the sensor out and measured it with my multimeter. The reading was 1080 Ohms - exactly what it should be, and the resistance increased with temperature just as it should. So then I checked the connections and the harness between the sensor probe and the control board for the upper oven. No issues. No open connection. No short. In a case like this, the GE service guide says a control board replacement is in order. Expensive!
At this point, before purchasing another board, I figure I better find out exactly what the error code means. So now I am thinking back to when appliances were easy to service, where manufacturers would stick a schematic on the back of the cabinet; is some useful information inside my oven? Lo-and-behold, I find two folded sheets taped to the wall inside near the control boards. It isn't a full-blown schematic, but it does provide some useful information. First, it tells me that F34 is "Upper difference between RTD temperature and Fine tune temperature is greater than 50F"; in other words, not a short. Second, it tells me that if I press the 1 and 5 buttons simultaneously within 5 minutes of booting up the oven, it will show me the probe temperatures. I do this while the oven is sitting at room temperature and the display shows me 74F for the lower and 11F for the upper oven. 11 degrees Fahrenheit??? For some reason the upper control board THINKS that the probe is at 11F not 74F. That explains it!
Now the temperature probes in these ovens are simple thermistors that increase resistance with temperature. At room temperature the reading is around 1080 Ohms, with the value increasing approximately by 2 Ohms with each 1 degree increase. Knowing this, I do a simple test where I add a 100 Ohm resistor in series to the probe input to the control board to see if this clears the error. On booting the oven with the resistor in place, I check the temperature reading from the oven by pressing the 1 and 5 buttons together and, sure enough, the reading is now 71F proving that the control board was not reading the probe resistance correctly. I test the oven with the resistor in place and it is working fine. The upper oven heats properly (I check with my own thermal probe) and there are no more F34 errors.
Ok. So what does this all mean? In my analysis, I discovered that the probe was working correctly and that the connections are all solid. I also know that the control board is communicating the temperature digitally to the LCD panel, and so the issue must be somewhere in the control board A/D conversion. I also know that I and others see these F34 errors occasionally at first until the oven stops working altogether. So what's really going on?
Here are my thoughts: According to the documents inside my oven, GE uses a 5 volt supply to the sensor probe to evalute the temperature by reading its resistance. My hunch is that the 5V regulator on these control boards - like most regulators - fluctuates a bit over time and may be adversely affected by heat within the oven cavities. Even slight changes in the voltage sent to the probe can have a fairly dramatic impact on the resistance read by the control board. In addition, using the oven's self-cleaning feature may accelerate changes to the voltage regulator, increasing the likelihood of this and related issues after a self-cleaning operation. In other words, heat and time are causing the board to go out of spec. And without the ability to recalibrate the control board, we are at the mercy of the board to maintain a near-perfect constant voltage throughout the oven's lifetime.
My guess is that, over time, ALL GE wall oven control boards drift to some degree with many of them ending up being replaced due to this issue. Depending on the nature of the drift - lower or higher voltages - you may see any one of the F3x codes displayed on your wall oven.
So here is what's baffling to me about this:
1. Why does GE not provide even their own service techs with proper error code descriptions?
2. Knowing that control boards may go out of calibration over time, why doesn't GE provide a simple mechanism to recalibrate the boards in the field? (NOTE: This is NOT the same as user temperature fine tuning as that simply masks the real problem).
3. Why is GE's response to any error where the sensor is known good to be, "Replace the (expensive) control board."
4. Given the prevalance of this problem, why hasn't GE issued a bulletin or recall?
Anyway, if you are seeing an F30-F35 error with your GE wall oven that becomes worse over time or occurs after a self-clean operation - and the probe tests OK - it is likely a problem with the control board where it is no longer reading the sensor properly due to the inability to recalibrate. In my case, I temporarily added a resistor in series with the probe to "recalibrate", and this modification appears to be working fine until I receive my replacement board.
Hopefully his information is useful.
At this point, before purchasing another board, I figure I better find out exactly what the error code means. So now I am thinking back to when appliances were easy to service, where manufacturers would stick a schematic on the back of the cabinet; is some useful information inside my oven? Lo-and-behold, I find two folded sheets taped to the wall inside near the control boards. It isn't a full-blown schematic, but it does provide some useful information. First, it tells me that F34 is "Upper difference between RTD temperature and Fine tune temperature is greater than 50F"; in other words, not a short. Second, it tells me that if I press the 1 and 5 buttons simultaneously within 5 minutes of booting up the oven, it will show me the probe temperatures. I do this while the oven is sitting at room temperature and the display shows me 74F for the lower and 11F for the upper oven. 11 degrees Fahrenheit??? For some reason the upper control board THINKS that the probe is at 11F not 74F. That explains it!
Now the temperature probes in these ovens are simple thermistors that increase resistance with temperature. At room temperature the reading is around 1080 Ohms, with the value increasing approximately by 2 Ohms with each 1 degree increase. Knowing this, I do a simple test where I add a 100 Ohm resistor in series to the probe input to the control board to see if this clears the error. On booting the oven with the resistor in place, I check the temperature reading from the oven by pressing the 1 and 5 buttons together and, sure enough, the reading is now 71F proving that the control board was not reading the probe resistance correctly. I test the oven with the resistor in place and it is working fine. The upper oven heats properly (I check with my own thermal probe) and there are no more F34 errors.
Ok. So what does this all mean? In my analysis, I discovered that the probe was working correctly and that the connections are all solid. I also know that the control board is communicating the temperature digitally to the LCD panel, and so the issue must be somewhere in the control board A/D conversion. I also know that I and others see these F34 errors occasionally at first until the oven stops working altogether. So what's really going on?
Here are my thoughts: According to the documents inside my oven, GE uses a 5 volt supply to the sensor probe to evalute the temperature by reading its resistance. My hunch is that the 5V regulator on these control boards - like most regulators - fluctuates a bit over time and may be adversely affected by heat within the oven cavities. Even slight changes in the voltage sent to the probe can have a fairly dramatic impact on the resistance read by the control board. In addition, using the oven's self-cleaning feature may accelerate changes to the voltage regulator, increasing the likelihood of this and related issues after a self-cleaning operation. In other words, heat and time are causing the board to go out of spec. And without the ability to recalibrate the control board, we are at the mercy of the board to maintain a near-perfect constant voltage throughout the oven's lifetime.
My guess is that, over time, ALL GE wall oven control boards drift to some degree with many of them ending up being replaced due to this issue. Depending on the nature of the drift - lower or higher voltages - you may see any one of the F3x codes displayed on your wall oven.
So here is what's baffling to me about this:
1. Why does GE not provide even their own service techs with proper error code descriptions?
2. Knowing that control boards may go out of calibration over time, why doesn't GE provide a simple mechanism to recalibrate the boards in the field? (NOTE: This is NOT the same as user temperature fine tuning as that simply masks the real problem).
3. Why is GE's response to any error where the sensor is known good to be, "Replace the (expensive) control board."
4. Given the prevalance of this problem, why hasn't GE issued a bulletin or recall?
Anyway, if you are seeing an F30-F35 error with your GE wall oven that becomes worse over time or occurs after a self-clean operation - and the probe tests OK - it is likely a problem with the control board where it is no longer reading the sensor properly due to the inability to recalibrate. In my case, I temporarily added a resistor in series with the probe to "recalibrate", and this modification appears to be working fine until I receive my replacement board.
Hopefully his information is useful.
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