Wrong Temp from Hotend

Hi,
Since this day I'm not able to print because my Printer sends a temp of 223°C but the hotend is cold.
So it will not heat up.
What can I do it worked fine on last week.
Checked cables seems good reattached the plug no change.

Any Help on this what can I do?

Thanks
Lars

It sounds like something partially shorting the thermistor. Can you measure the thermistor resistance at room temperature?

I have no Multimeter at the moment.
I have reattached all cables now, and no one was in my flat since last week Friday and it worked well there...
What a shame, want to start Printing Halloween stuff today..

Made a different check,
I have now wired the two green transistor cables directly to the ETEMP GND/SIGNAL on the Melzi and I get the same confusing results.
What now can I fix this by my own or do I have to order a new preassabled Extruder?

Lars

Is there any contamination on the thermistor cement? The only time I have known a fault like this is when molten plastic soaks into the cement and then carbonises.

Another possibility is the heatshrink on the thermistor leads has got too hot and burnt. You would need to cut away the outer heatshrink to check those joints.

Does it give a MINTEMP error when you disconnect the thermistor wires. I.e. is the Melzi working?

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[www.hydraraptor.blogspot.com]

I get no error I only get 0°C
I have now detached the entire extruder stuff, the heat shrink (large Red one) is looking got no burning or darker parts from outside.
Not sure how to check the Cement without cut the Heat shrink...

The Golden Extruder-end looks brown/black partly.

All other functions are working good can it be a part of the Melzi and how I can check this.
Tomorrow at work i will check with a multimeter my Extruder but if you say you had never something like this.

BR
Lars

Thans for your Help Nop

Looks like that there is a litte bit water inside in one of the plastik tubes...there are some small drops.
Can this cause this error?

Was able to lift up the heatshrink an made a picture of the hotend!

Edited 2 time(s). Last edit at 10/22/2013 02:16PM by Psike2k12.

0C is the correct reading for an open circuit input, so the Melzi is working. Not sure why you don't get a MINTEMP error, but that is not important.

The red stuff isn't heat shrink. It is self fusing silicone. It looks like there is burnt plastic under it, so it looks like the hot end has been leaking. That has probably contaminated the cement and shorted the thermistor.

I don't think it will be water. I think it is some other volatile compound that boils off burnt plastic and then condenses.

It can be repaired, but it is a big job. It will need stripping down and re-assembling to cure the leak and the thermistor will have to be drilled out and a new one cemented in. I think the hot end must have been faulty so I will send a replacement.

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[www.hydraraptor.blogspot.com]

I have no measured the values,

I get from the thermistor instad of 100kΩ ---> 271,5Ω .... that is why I get this large temp Values.

BR
Lars