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Hot end heating problem

Posted: Tue Sep 03, 2013 11:05 am
by QuantumVenom
I am having a problem with the hot end. I turned the printer on this morning, loaded my file, then set the nozzle and bed temp then hit set. The nozzle reached about 175 (my target was 185), then all of a sudden it just shut off and the temperature started to decrease. I haven't been able to get it to start heating again. Did something short circuit or do I need to replace the thermistor (I hope not). I've checked all the connections I can without removing the hot end setup.

Any ideas?

Thanks

Re: Hot end heating problem

Posted: Tue Sep 03, 2013 2:33 pm
by gannon
Do you get any errors reported? Can you move any of the axes?
I can only think of 3 main parts that could cause this issue. Wiring being the most common I have dealt with.
1) Thermistor issue (Wiring issue, damaged thermistor)
2) Heater issue (Wiring issue, damaged resistor / heater cartridge)
3) Power issue (PSU failure, blown FET)

Re: Hot end heating problem

Posted: Tue Sep 03, 2013 2:42 pm
by Orias
I would recommend powering down the printer, then disconnect the hot end from the wiring harness. Test the hot end for the proper resistance- the smaller orange wires are for the thermistor and should read ~100k at room temperature. The larger red wires are connected to the heater resistor and should read between ~4-7 Ohm. Reconnect the hot end wiring to the wiring harness. Make sure that the pins are fully seated within the connector housing and if everything tests out bring the printer back up to extrusion temperature. You can test the hot end heater resistor when it's attempting to heat, by checking the two contact points on the red wiring through the connector. Make sure you do not short anything to to orange connectors/wiring.

Re: Hot end heating problem

Posted: Tue Sep 03, 2013 2:54 pm
by QuantumVenom
Thanks for the replies. I don't get any errors and I can still move all three axes. PrintRun is still reading the temperature correctly so I think it is something with the resistor, but I'll be checking both the thermisor and resistor tomorrow when I have a chance.

Thanks again.

Re: Hot end heating problem

Posted: Wed Sep 04, 2013 10:22 am
by QuantumVenom
I've tested the thermistor and resistor both while turned off and while trying to heat. Nothing seems to be wrong, the correct resistance is there. I'm not sure what to do...

Re: Hot end heating problem

Posted: Wed Sep 04, 2013 10:38 am
by QuantumVenom
What is the voltage across the heater terminals on the board supposed to be. I'm only getting about 4.5 mV and I'm not reading any current. Something seems a little off there.

Re: Hot end heating problem

Posted: Wed Sep 04, 2013 10:45 am
by jebba
Should be 12V coming from the electronics.

Re: Hot end heating problem

Posted: Wed Sep 04, 2013 10:49 am
by QuantumVenom
Does that mean the power supply is messed up? I just checked the back of the board and it doesn't look like anything is fried.

Re: Hot end heating problem

Posted: Wed Sep 04, 2013 1:55 pm
by Orias
There are two fuses you can check, on the right hand side of the board in this image: http://reprap.org/mediawiki/images/5/5c ... nn-all.jpg Is the hot end thermistor connected to T0 when you are testing? It should be able to read the ambient temperature. If it's reading correctly, is it still reading the same when you rest the voltage at Extruder 0 Heat? If so, please email us at support@lulzbot.com and we can figure out what needs to happen.

Re: Hot end heating problem

Posted: Thu Sep 05, 2013 8:53 am
by QuantumVenom
I've determined it's a problem with the main connection between the board and the nozzle. I was playing with that connection while it was trying to heat and I noticed a few things. 1, the connection itself became somewhat hot and 2, depending on how the connection was moved, it would either be heating or it wouldn't be. I disconnected it and noticed there was some heat damage on the board side of the connection. I attached a picture showing the damage. What would cause this?

Thanks,
Chris