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thermistor Issue

Discussion in 'Troubleshooting' started by chn9292, Dec 21, 2020.

  1. chn9292

    chn9292 New Member

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    thermıstor shows 190 C degrees in room tempature. what kind of problem could be in there ? because of this ı can not make PID. Heater warm it always more than normally.
     

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  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Bad thermistor or wiring harness loose/bad.
    Make sure the thermistor wire is landed correctly on the board at the base of the carriage (trace it back up). If it were to get loose or disconnected that might do it. If you need a new thermistor PartsBuilt.com has them,
     
  3. chn9292

    chn9292 New Member

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    I've already replaced it new one. could it be on ribbon from mainboard?
     
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The thermistor does have a ribbon cable from the main board to the uptown board (one at top of extruder carrriage) as well as wiring internal to the carriage that goes down to the downtown board (near extruder).

    You can trace those to make sure they are landed properly. Worst case it is a fault with the control board.
     
  5. Lance Weston

    Lance Weston Active Member

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    After you have done all of the obvious we can go deeper. The resistance of the thermistor goes down as the temperature goes up. At 190C it would appear there is neither a break or a short. I have attached two pictures, one of the e the thermistor input circuit and the other of the 16 pin header. There are a few reasons that the thermistor can read wrong. First get a meter and measure pin 15 to pin 5 on the " To Uptown Adapter" header. The board should be removed from the Robo. The header is numbered 1,3,5,9 etc left to right on the inside edge of the header with pin 1 marked on the left. Measure the resistance of pins 1 to 5, flip the probes and remeasure. The readings should be 4.3K and 4.7K. Now measure from pin 15 to pin 13 and flip the probes and remeasure. You should ge 4.5K and 7.5K.

    We are looking for a shorted/leaky capacitor or a damaged 4.7k pullup resistor. If neither of these is the problem, go to the R2 and and insert fine wires in pins 15 and 13. Now measure the resistance, it should be 80K to 100k. If it is not then the trouble is somewhere between the cable and connector and the thermistor.

    If all measures correctly then the problem is the board and we have one more way of getting you going. I will modify the code to use the other hotend thermistor and you will plug the hotend into the other thermistor connector. Let me know.

    It also occurred to me that your code may have become corrupted. In the attached thermfix.zip I have included the original code and modified code that swapps T0 and T1. First try the original code. Load it onto a USB drive and plug it in. Then from the LCD go to files and load and run the hex file. This will return your code to original. If you have ruled out all else then load my second code with T0 and T1 swapped. Now just plug the hotend thermistor into the other thermistor connector. Of course you have to recalibrate the PID.
     

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    #5 Lance Weston, Dec 21, 2020
    Last edited: Dec 21, 2020
    mark tomlinson likes this.
  6. chn9292

    chn9292 New Member

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    I have measured 1 to 5 and 13 to 15 pins. ı got 3,8k 1 to 5 and when i flip there is no value. 13 to 15 is 4,7k and there is no valuse at flip. Also 1 to 5 and 13 to 15 are not same direction.
     
  7. chn9292

    chn9292 New Member

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    in generally i can not get value when ı flip probes.
     
  8. Lance Weston

    Lance Weston Active Member

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    Your measurements are odd and I do not know what to make of them. The 4.7k suggests that the pullup wiring is correct on the board with no board damage. If the 15 to 13 on the cable is open and you do not measure 80k to 120k then the cable to the hotend is probably bad. The fact that your measure 190c suggests it is not open. The fix is to cut the 16 pin header off the end of the cable with a very sharp scissor. First taking a picture so you that can put it back on correctly. Carefully take the header apart and remove the ribbon cable. Now crimp that header on the remaining ribbon cable. This is a common failure.
     

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