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MINTEMP/Thermistor Issue  

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pcklbgr
(@pcklbgr)
Active Member
MINTEMP/Thermistor Issue

My MK3S started showing the MINTEMP error this morning (the thing was still printing fine yesterday evening).

I ended up measuring resistance of both hotend & bed thermistors.
Hotend thermistor measures ~170kΩ while bed thermistor - ~105kΩ. Which means one of those is clearly out of whack.
Per MINTEMP error and MINTEMP BED KB it ought to be about 80 kΩ - 125 kΩ.

I also tried wiggling the hotend thermistor cable while everything was still plugged in - it showed normal temperature for a bit, printer even claimed that MINTEMP error was fixed and asked for a restart. I was unable to replicate that with multimeter hooked up, wiggling might have borked the cable more.

Does this mean I should replace my thermistor?

Posted : 03/03/2021 11:10 am
JoanTabb
(@joantabb)
Moderator
RE: MINTEMP/Thermistor Issue

If the ambient temperature is above 15C, Mintemp is normally caused by a loose connector or a breaking wire. 
repeated flexing of any wire, will eventually lead to a failure. 

however  the failure normally starts off as an intermittent problem. which can be difficult to prove. 

I would consider replacing the wires with flexible silicone insulated  wire, and that fix, will usually last for AGES, as the flexible silicone insulated wire is less susceptible to work hardening and fatigue in a flexing situation. 

below is a diagram for a fix I do to Pinda cables... but the idea is the same,  simply replace the section of cables that flexes and make sure the joints are in areas that don't flex. 

If you have the capability to crimp new connectors on the ends of the wires  that is a better option

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 03/03/2021 12:48 pm
JohnnyGreens
(@johnnygreens)
New Member
RE: MINTEMP/Thermistor Issue

I also have a thermostor issue with my MK3S +. I damaged a wire changing a nozzle. I picked up another thermistor from Voxel Factory here in Vancouver and installed it which was simple. I powered up the printer and started preheating to load PLA. I watched until it hit 125C then start cleaning up my tools. Soon after I could smell burning and looked at the extruder to see smoke was pouring out the nozzle. The mini temp error message was displayed And the temperature read 180C.I loosened  the grub screw and repositioned the sensor then plugged the cable back in to the board and tried again. This time the temperatures rose fairly quickly to about 160 then crept slowly Up to 180 when the mini temp error message appeared again.Thinking I more than likely screwed something up I picked up another thermistor and installed it but the temperatures started creeping up slowly from 160 and I’m getting the error message again at 180c.

 

thoughts?

Posted : 03/03/2021 5:17 pm
JohnnyGreens
(@johnnygreens)
New Member
RE: MINTEMP/Thermistor Issue

Support ticket started.I will post the results 

Posted : 04/03/2021 4:38 pm
pcklbgr
(@pcklbgr)
Active Member
Topic starter answered:
RE: MINTEMP/Thermistor Issue
Posted by: @joantabb

If the ambient temperature is above 15C, Mintemp is normally caused by a loose connector or a breaking wire. 
repeated flexing of any wire, will eventually lead to a failure. 

however  the failure normally starts off as an intermittent problem. which can be difficult to prove. 

I would consider replacing the wires with flexible silicone insulated  wire, and that fix, will usually last for AGES, as the flexible silicone insulated wire is less susceptible to work hardening and fatigue in a flexing situation. 

below is a diagram for a fix I do to Pinda cables... but the idea is the same,  simply replace the section of cables that flexes and make sure the joints are in areas that don't flex. 

If you have the capability to crimp new connectors on the ends of the wires  that is a better option

regards Joan

I suspect that wire for my thermistor broke at the point where it exits the thermistor "cartridge".
Hindsight being 20/20 - I assembled it sort of wrong, there was no slack left, considering how much loose wire I got at the electronics box end.

I ordered a new one from Prusa store, hopefully I'll manage to install it properly.

Posted : 05/03/2021 10:13 am
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