1 Topic by jgilldev (edited by jgilldev 2014-02-07 06:48:31)

  • jgilldev
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Topic: Thermistors on extruder keep blowing out. PLEASE HELP!

Hi All,

I will try to keep this as brief as I can without leaving out too much detail.
Previously after my SD2 extruder assembly falling to pieces I ordered a new one, after waiting for months it finally arrived and I installed it as per the instructions I found on these forums and also referencing the instructions on the SD wiki. One point to note here is that the "fully assembled and tested" extruder assembly did not have a thermistor attached when it was delivered, I ended up having to use the thermistor from the old assembly.
After it was installed I turned on the printer and started up the software, as per the usual procedure. As soon as I turned on the extruder heater I noticed smoke coming from the new assembly. Upon investigation I found that the thermistor had died. I have since had both of the replacement thermistors burn out in the same manner only a minute after turning on the heating to the extruder.

I have done a full test of everything I can think of, I have gone over almost every component with the multimeter testing resistance and voltage and everything has come up fine. I have also updated the firmware to the current version on the SD website. I have uninstalled and reinstalled the repetier host software and drivers from the SD website.

One peculiar thing is that when the first thermistor blew, the temp was sitting at 119.40 degrees, every time that I have tried a different thermistor the temp reading in the software is always showing the same number of 119.4 degrees.
the extruder still heats up fine but I am not able to get any temperature reading from it, it just constantly shows the same temp all the time now.
This leads me to suspect that there may be an issue with the 644P chip or perhaps part of the circuit between the thermistor and the 644P chip, which is giving the software a constantly false reading.

Any help as to why the thermistors are getting fried and what can be done to fix the issue would be a tremendous help. So far I have not been able to print anything for at least 6 months, it is very discouraging.

Thanks. smile

2 Reply by ronsii

  • ronsii
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Re: Thermistors on extruder keep blowing out. PLEASE HELP!

Have you metered the two wires going to the thermistor?

1. across the two wires for voltage
2. from one wire to GND for voltage
3. from other wire to GND for voltage

Measure these three things with the hotend OFF and also with it ON

Do these measurements with both hotend and thermistor disconnected at printhead

3 Reply by jgilldev

  • jgilldev
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Re: Thermistors on extruder keep blowing out. PLEASE HELP!

ronsii wrote:

Have you metered the two wires going to the thermistor?

1. across the two wires for voltage
2. from one wire to GND for voltage
3. from other wire to GND for voltage

Measure these three things with the hotend OFF and also with it ON

Do these measurements with both hotend and thermistor disconnected at printhead

Thanks Ronsii, I will give that a go this evening and let you know how it goes.

4 Reply by pastprimitive

  • pastprimitive
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Re: Thermistors on extruder keep blowing out. PLEASE HELP!

If it is your 644 a 1244p is $10-$15 with the bootloader pre loaded.  Great excuse for upgrading your chip to allow for many more upgrades like a LCD+encoder, and other stuffs:)

5 Reply by jgilldev (edited by jgilldev 2014-02-07 06:47:24)

  • jgilldev
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Re: Thermistors on extruder keep blowing out. PLEASE HELP!

Well in good news I found that it was a faulty connection on one of the wires, which I have now fixed. Bad news is that I am still waiting for my new replacement thermistor to arrive, but I ordered some extra ones to keep as spares as well. However this has been a great learning experience for me.

pastprimitive wrote:

If it is your 644 a 1244p is $10-$15 with the bootloader pre loaded.  Great excuse for upgrading your chip to allow for many more upgrades like a LCD+encoder, and other stuffs:)

I think I am going to upgrade the chip as per your suggestion Pastprimitive. After all the tinkering I have done with it lately I am much more confident in performing some more upgrades. Do you have a website for the upgraded chip by any chance?

Thanks again for your help guys! It is extremely appreciated.  smile