temperature reading problem

Hi there, I'm new to this site and also new to 3D printing. I recently ordered all the parts to build a prusa I3. I have everything assembled and started hooking up the electronics. I currently have the lcd hooked up and working along with the x, y, z, and extruder motors. I also have my heated bed thermistor and my hot end thermistor hooked up. That's when I noticed a problem. My heated bed thermistor is working and reading the right temperature but my hot end thermistor must not be working because I'm getting a max temp error. I have it hooked up to the T0 slot. But it's not the thermistor itself because when I plug it into the T1 slot for the heated bed it works fine. It's almost add if the T0 slot on my ramps board is fried or not working. Or do I need all other electronics hooked up for everything to function properly? Any help would be greatly appreciated since I'm completely new to this hobby.

Did you adjust your config file for the appropriate thermistor type? Every thermistor has different temperature resistance curves for the temps it's to measure.

They are both the same thermistor. Just one plugged into the T0 port and one plugged into T1. T1 which is for heated bed reads 26 degrees Celsius according to the lcd. The lcd also reads the hot end as 500 degrees Celsius which must trigger the max temp error. It's acting as if there's no thermistor plugged in for the hot end.

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cdru
Did you adjust your config file for the appropriate thermistor type? Every thermistor has different temperature resistance curves for the temps it's to measure.

using marlin how do I check/fix this?

Did you load Marlin onto your board yourself? If you did, check Configuration.h for the TEMP_SENSOR_0 and TEMP_SENSOR_BED lines. If your thermistors are the same they should each have the same value.

If you didn't load Marlin, you'll need to download the Arduino IDE and the Marlin firmware. Google for Prusa i3 Marlin configuration for a tutorial, like this one.

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Yes I did load it on myself. Thanks I'll check that out.

Hey thanks for the help. I fixed it, it was in the code. Somehow I had a negative value in the temp sensor line of code. That's what screwed it up

I ran into another problem. After messing around with the marlin firmware and loading it into the arduino board I noticed my extruder motor is not working. It's not the wiring because when I hooked it up to the x axis slot it works fine. I'm guessing I screwed up something in the marlin firmware again. Any idea as to where to start looking in marlin. Like which line of code would deal with the extruder motor or something that would cause this issue.

Do you have the hot end heated up? Marlin has a feature to prevent cold extrusion.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

Thermistors are easy to damage.
Try hooking your bed thermistor into the hot end spot and see if you get a reading and if your extruder will then move (I disable the cold extrusion lock on mine).

How do you disable cold extrusion lock?

It's been a while, but it's something like "disable unsafe extrusion" in configuration.h.

Edited 1 time(s). Last edit at 08/10/2014 07:39PM by sheepdog43.

M302 allows cold extrusion.

[reprap.org]

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Thanks, that was it. Once I allowed the hot end to heat up everything worked fine. Anyone using a j-head hot end who can give me any temperature suggestions? I'm using 1.75mm PLA.