Heatbed MINTEMP / Thermistor
I have a MK3S with MMU2 and problems with the Heatbed MINTEMP.
In the last weeks I often had the error with the garbled screen (with all those funny characters on screen) in the middle printing. Octoprint shows: "Temperature heated bed switched off. MINTEMP triggered ! - // action:cancel"
This sometimes happens 5 times in a row and then suddenly it works 10 times in a row… Very strange.
What I did:
- Reset Printer and MMU
- Flashed new Firmware on Printer and MMU
- Checked heatbed cables
- Read a LOT in the forums
With the newest Firmware 3.9.0 the garbled screen does not show anymore. But still stopps the Print with "M112 called. Emergency Stop." on the LCD. Octoprint still shows the same message as before.
Very strange is, that it always happens at the same point in printing. For example with one particular g-code it often happens when printing the skirt about a third of the way (see picture).
I attempted to print the included g-code-file 7 times now:
- 1.Time: all goes well
- 2.Time: stopps when printing skirt
- 3.+4.Time: all goes well
- 5.+6.Time: stopps when printing skirt
- 7.Time: all goes well
This happens with all kind of g-codes. I have them sliced with the most recent version of PrusaSlicer.
I can’t find out why it sometimes works and sometimes not…
When I wiggle the heatbed cable nothing happens. It is also plugged firmly in to the board. So I am not sure it really is the thermistor cable as mentioned all over the forums.
I even tested the cable with my multimeter. And I could produce an error but only with a LOT of abuse. See here:
Thank you very much for your help… I have no more ideas…
Greetings from Switzerland
Best Answer by WorstCase:
SOLVED!
I got a new thermistor from Prusa and replaced it according to the Knowledge Base:
Now everything works fine again! Was probably the thermistors cable that was broken just a little bit.
RE: Heatbed MINTEMP / Thermistor
Example G-Code (only first 5000 lines): https://pastebin.com/VBvrsXVa
(Somehow I can not upload g-code files)
RE: Heatbed MINTEMP / Thermistor
I just got an answer from Prusa Support:
[...] We will have to replace the heatbed cables. I will initiate a replacement - we will send you a new one. [...]
If you are having the same problem: There also is an article in the Knowledge Base about the replacement:
I will post an update after I have replaced the thermistor.
RE: Heatbed MINTEMP / Thermistor
SOLVED!
I got a new thermistor from Prusa and replaced it according to the Knowledge Base:
Now everything works fine again! Was probably the thermistors cable that was broken just a little bit.
RE: Heatbed MINTEMP / Thermistor
I had the same issue - Error M112 and MINTEMP.
It turned out to be a faulty head bed thermistor cable. The cable is in constant motion, and over time, the strands are going to gradually fracture anywhere they are bent by more than a certain amount.
It turns out that where it is clamped at the heat bed end, the cable is bending a lot, because it's constrained at one end. Eventually the copper strands had all broken internally (while looking perfectly fine outside - the cable insulation is pinched, but essentially intact) and when flexing it with a multimeter attached, I was seeing intermittent losses of connectivity.
Prusa really need to put some kind of flexible strain relief where it enters that clamp to prevent this kind of bending. I can see this being a common failure mode. There's nothing to prevent you from buying or printing your own however.
So what you really need to do is just replace the wire running between the connector and the thermistor, not the whole assembly. Assuming you have some dual core cable which is heat resistant (probably 150 degC rated) and some shrink fit tubing. However, you need to solder the joins somewhere that doesn't flex, (inside the housings at each end) or the replacement cable will fail even sooner.
RE: Heatbed MINTEMP / Thermistor
A great tip for you all, my thermistor cable for the heatbed also failed. I found one of those old fashioned computer mouse with a fairly thick cable and replaced my the thermistor cable with this. The mouse cables are designed to deal with significant constant movement and rarely fail and will out perform any thermistor cable.