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Repetier 0.92 and 100K thermistor for bed temps
#1
I've been fighting my printer to get accurate temps on the heated bed after breaking the stock thermistor.

I understand that the stock thermistor is 500k, and that I should be able to add custom thermistor tables to the configuration.h to get more accurate temps, but I bought the generic reprap 100k thermistor (EPCOS 100K Thermistor [B57560G1104F], specifically from Mouser [871-B57560G1104F000]) and the thermistor technically works, but reads really high temps at room temperature (~80C). When I hold the thermistor between my fingers, the temps rise, but no matter how I try, I can't get the thermistor tables anywhere near accurate.

Using the thermistor table available at ( http://reprap.org/wiki/Thermistor#EPCOS_...104F000.29 ) in USER_THERMISTORTABLE2 and defining HEATED_BED_SENSOR_TYPE as 7 to reference the proper table sets the thermistor at 0C and doesn't change when heat is applied. Changing the sensor type to 1 gives me the ~80C temps, but obviously that isn't accurate.

So where do I go from here? Is there some kind of damage to the motherboard? Something I'm missing in the config file?
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#2
Davinci is not a RAMPS, resistor on RAMPS is 4.7K, and if I am not wrong on DAVINCI it is 47K for bed - different than for extruder unlike RAMPS

You are using generic tables for RAMPS (which are not working for DAVINCI) not custom tables. Custom table is done using a thermometer and mesuring tenmperatures according sensor values to build a custom table like we did here : https://github.com/luc-github/Repetier-F.../issues/83

so 2 solutions :
1- you change the resistor on DAVINCI board
2 - you build your custom table as so far no one shared any until now for your sensor for the bed
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#3
I'm confident enough with a soldering iron to do a resistor replacement on the motherboard, is that what you're suggesting? If so, I'd need to replace a 47K resistor with a 4.7k? Do you happen to know which one, or do I need to do some tracing?

I'm also not opposed to helping build a proper table for other people to use to replace the bed thermistor, I'd just need to know what process to follow to measure the resistance and where to do so (as well as any suggestions for how to accurately apply and measure the temperature).
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#4
all answers are in thread I have copied - bed resistor is R28 for old and new generation - position is also mentioned in thread
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#5
Gotcha. I'll check it out then, thanks for the help!
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#6
I just finished replacing the resistor on that circuit, and the thermistor appears to work flawlessly. I still have another 1.0 to modify, but if you want I can measure resistance at some temperatures to build a table for a 100k thermistor ont he bed still. Otherwise I'll end up doing the same replacement on the other board.
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#7
Happy for you it works
Well it would be great for people who cannot rework the board like you did - it is up to you thanks
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