Extruder Board Temperature Troubles

For a few weeks already, my boards have been working fine. This afternoon, though, I started having issues with my extruder board. It seems that it keeps reporting 143c when the heater is off. I unplugged the thermistor, and it still shows 143c. When I have the thermistor plugged in, and start heating my extruder, the temperature does go up. However, it never drops below 143c.

I have absolutely no idea what's wrong. I tested the thermistor with my multimeter and got 90 kohms (which seems normal to me). I reuploaded the firmware and double checked my beta and nothing seems out of the ordinary there.

I'm using the MakerBot extruder controller with 5D firmware. I'm using a 100k thermistor, also from MakerBot.

Here is my beta
#define NUMTEMPS 20
short temptable[NUMTEMPS][2] = {
{1, 864},
{54, 258},
{107, 211},
{160, 185},
{213, 168},
{266, 154},
{319, 143},
{372, 133},
{425, 125},
{478, 116},
{531, 109},
{584, 101},
{637, 94},
{690, 87},
{743, 79},
{796, 70},
{849, 61},
{902, 50},
{955, 34},
{1008, 2}
};


If you have any ideas, please let me know.

Most likely you had a short to the heater which damaged input of the micro. A leaky filter capacitor could also have the same effect.

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[www.hydraraptor.blogspot.com]

So I guess the nichrome cross wires with the thermistor somewhere. Any suggestions on how to get around this?

If you have damaged the input then you either have to find a spare analogue pin and modify the firmware, or replace the micro.

---

[www.hydraraptor.blogspot.com]

I had a similar problem before and found that I did have a short between my nichrome and my thermistor. Then another one when the bulb on the thermistor would get twisted, creating a short with the thermistor leads leading to the bulb. My solution was to take the thermistor off, lay it out flat in a v shape and put some tape on both sides then reattach it to the barrel. But only attach it with a few pieces of tape at the end of the barrel, around the bulb. Leaving the rest of the 'body' to kinda hang off so it will not contact the heater barrel or the heater leads, and if it does, the tape might save it for a few seconds longer.

Since the extruder sits in a box on my laser cut mendel there isn't a worry that it will snag on something, or get pushed into hot stuff.