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Thermistor for Heated Bed Incorrect reading

Posted by jtreg 
Thermistor for Heated Bed Incorrect reading
August 26, 2014 08:38AM
Hi all,

I connected up a new RepRapDIscount Full Graphics controller up to my Ramps 1.4 (I have a Prusa i3). All was hunky dory (for the last year, actually) - I noticed the conroller showed up the bed reading temp at 73-74 degrees C at room temperature. No heat until I raided the threshold above 74... I did uncomment the necessary 2 lines in Marlin to get Graphics controller working, that was all. I removed the graphics controller and returned to my trusty Ubuntu/Repetier setup. Same result, thermistor reads 73. OK off with heater test thermistor - it reads 116 on 200K ohm scale - 116K ohms, right? Its a EPCOS NTC 100k thermistor. I presume its faulty? In which case, I will replace it. If not... what could be wrong? I dont think I changed anything in Marlin (by accident)....

Anyway, any advice would be most appreciated.

Thanks
Re: Thermistor for Heated Bed Incorrect reading
August 26, 2014 06:07PM
116k seems reasonable for a cold bed. You may have a faulty channel on the Arduino - you could try using T2 for the bed (re-map the pins) or swap with T0 just to test. Other than that, maybe the graphics controller has an issue - guess you could take it out of circuit and just use your laptop to see if the problem disappears.


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Waitaki 3D Printer
Re: Thermistor for Heated Bed Incorrect reading
August 27, 2014 12:49PM
Hi Waitaki
I swapped t1to t0 still shows incorrect temp. I have abandoned the graphics board for now still no joy... Even replaced the thermistor.
Re: Thermistor for Heated Bed Incorrect reading
September 01, 2014 08:20AM
So, are you saying that when the hot-end thermo is plugged in to T0, it shows the correct room temp reading?


_______________________________________
Waitaki 3D Printer
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