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Question about temperature 'def'

Posted: Thu Jul 19, 2018 10:18 pm
by baba
I read a lot of the great background here on the 'def' problem with the temperature reading. I checked some things out per the past experience, but so far I do not think I have the same problem. Here is what happens.

I have been printing an object that has 9 parts. I have printed 3 of the parts with no problems. They ranged from 1-4 hours. I get to the first of 3 big parts, and it will take abut 7 hours. It failed on me about 4% in with the 'def' being displayed for both temps, and the printer moving but not extruding. I tried again, failed again same way at about the same point. I re-sliced it (using cura in mattercontrol both times) and watched it a third time. It failed again in about the same place. The bed temperature started dropping from its set point of 75, just going down slowly from 75 to about 50C and then the whole thing just went 'def'. The bed heating light was on the whole time, and it felt hot. I tried to use a kitchen thermometer to see how hot, but I couldn't get a good reading.

I wiggled the wires and what not trying to get it to go 'def' again, but no luck. I don't think it is a short because the other 3 objects I printed with the same settings covered about the same bed area and went taller than the failed part. I printed them all in PETG at 255C, bed 75, and cooling fans enabled. I thought perhaps the layer fans were doing too much and the part of the print where it was failing is right over the thermister. So I am trying again right now with the layer fans disabled. It has made it to 75% complete, bed still at temp, no 'def' obviously.

Thoughts on what could be gong on here?

Brian

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 7:32 am
by baba
Well the print completed with no 'def', but it looks like garbage without the layer fan on. trying again with the layer fan on, but I can already see the temp dropping. I went in and turned the fan off on the little LCD, and the bed temp instantly started to come back. What gives here? I've got tons of print time on this thing, mostly with PLA but also with some ABS and this has not been a problem before. PLA also uses the layer fan but my last several prints with that have not been an issue. How could the layer fans be affecting bed temperature reading, besides the obvious blowing of cold air?

Brian

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 7:48 am
by joe
Hi baba, > the 'def' signal means that the thermistor is not returning a valid signal to the control board. It's either an open circuit or a dead short. Since it falls outside of the acceptable range, the board shuts down the heater circuit to prevent runaway thermal damage.

Note that if either the hot end thermistor OR the heated bed thermistor have a problem, both heaters will be shut down. This can cause you to believe that you have two bad thermistors, when in fact only one is troublesome.

One common problem occurs at the hot end thermistor, particularly on e3dv6 heads. The thermistor is inserted into a hole in the aluminum hot end, the legs bent at 90 degrees, and a screw tightened down to hold the thermistor in place. The leads are typically insulated with a thermal protection sleeve. If this sleeve has slid out of place or become damaged, the thermistor lead can ground through the aluminum hot end, thus providing a bad reading. Alternately, enthusiastic overtightening of the screw can break a lead.

To troubleshoot the problem, check the resistance on the two thermistors with an ohm meter. If either one is reading infinite or near zero, you've found the troublesome thermistor. Check it for signs of visible damage, and repair or replace according to what you find. - from another post.
No amount of reslicing or calibrating will fix a "def".

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 7:57 am
by baba
THanks, let me ask another question or two to follow up

1. since the hot end temp reading seems steady, and it is the bed temp that drops with the fans on, do I assume it is the bed thermister that is bad? I can test both still, but it seems to me the issue is the bed temp dropping and then causing the 'def'
2. My hotend is the HE280 which came with my Rostoc Max V3. Does that change your advice? I can't believe I forgot to include that in the original post.

Brian

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 8:33 am
by baba
Perhaps I'm still barking up the wrong tree, but 25% fan speed seems to be the magic number where the bed temp remains relatively constant. Higher than this and it drops pretty fast.

-Brian

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 10:59 am
by geneb
Just for grins, check your power supply output when the hotend and bed are both heating up. That's going to be where the max draw is happening. If it's less than 11.8-12v, you may have a power supply issue. If you've got one of the non-ATX supplies, there's an adjustment pot on it (where the terminal block is) that will allow you to turn up the voltage. If you've got an ATX supply, you may need to replace it. Also check the heated bed wiring at the RAMBo - the terminals can come loose and cause all kinds of grief.

g.

Re: Question about temperature 'def'

Posted: Fri Jul 20, 2018 3:35 pm
by Xenocrates
Def can also mean that it believes the temperature is decoupled, meaning that it's pumping in more heater power, and not seeing a temperature response. So if you have the center of the bed uncovered (where the thermistor is), and fans blowing, the thermistor can lose heat rapidly, and cause a decoupling error. You get the same problem if the fans gradually overwhelm the bed heater and push the temperature downwards. They can be cured to some extent by either reducing the fan, or increasing heater power. A heat spreader will also help, partially due to thermal mass, and partially due to evenly distributing the heating power to prevent local hot and cold spots.

Re: Question about temperature 'def'

Posted: Sat Jul 21, 2018 8:05 am
by joe
Xenocrates wrote:Def can also mean that it believes the temperature is decoupled, meaning that it's pumping in more heater power, and not seeing a temperature response. So if you have the center of the bed uncovered (where the thermistor is), and fans blowing, the thermistor can lose heat rapidly, and cause a decoupling error. You get the same problem if the fans gradually overwhelm the bed heater and push the temperature downwards. They can be cured to some extent by either reducing the fan, or increasing heater power. A heat spreader will also help, partially due to thermal mass, and partially due to evenly distributing the heating power to prevent local hot and cold spots.



A decoupled error shows as DEC. def is a thermistor fault, open circuit or dead short.