Thermal issue - Over temperature but display is normal.
MK3s+ kit purchased in March of this year.
In the last 24 hours I have had a strange issue. I was printing sample tags for my different PETG filament I had recently purchased. Things were going good until the last three tags. I thought the filament was damp and started drying the last three rolls and working on tying to get my Satin Sheet clean since the last print was not coming off.
I tried to do a different print with material that I had printed with yesterday to see if that would help clean the sheet when I came across the issue. I put in the Prusament filament and when it was loading, the filament was coming out in blobs and not a string as normal. It wasn't bubbling as I believe wet filament should but as a liquid and dripping. Which is what I saw just before I quit yesterday.
I thought about it and thought that it was strange to see this and the smell and filament smoking, I decided to look at the temperature. I have a type K thermal couple and stuck it on the side of the print head. You can see that even with a slight bit of contact, the temperature is quite high in comparison to what the display says. 195 vs. 243. This is just a test temperature I selected for testing purposes
Below is a picture of the hot end and nozzle. In the circle, you can see thermal couple touching the head. I also checked the temperature at the nozzle to aluminium block which is about the same temperature. You can see where the green arrow is pointing that the print head housing has been damaged from heat. The aluminium block is also dark in colour.
For reference, below is the temperature and RH% in the filament storage box. All the filament I was printing with when the problems started are in this box.
I have not upgraded the firmware on the printer due to all the thermal issues that have been reported, so I am still using what was on the printer in March when it arrived. As expected, Ponterface shows the same temperature data as the printer.
I have rebooted the system. I have checked for loose connections. I have had two intermittent thermal issues and two print fan issues in the past couple of weeks. I have installed the modified cooling fan housing as I am printing in an enclosure due to dusty environment and I find that it has helped with bridging. After the previous printer temperature warnings, I pulled the Einsy board out and double checked all the connections. Set screw on the thermistor is snug. Today's tests were with the enclosure open and the printer just turned on to load the filament.
My theory is that the thermistor is failing and I will check the resistance later. Or there is a problem with the Einsy board since I have had both thermal and print fan intermittent issues.
Where do I start on troubleshooting this or just get in touch with Prusa since the printer is under warranty.
RE: Thermal issue - Over temperature but display is normal.
get in touch with prusa probbaly a faulty thermistor
Please help me out by downloading a model it's free and easy but really helps me out https://www.printables.com/@Hello_474427/models
RE: Thermal issue - Over temperature but display is normal.
That is my plan, after I do a couple of tests today. I have a couple of thermistors, without the brass sleeve, that are from an older design hot end and will test one of them today. It is a quick test.
The other intermittent issues are still a concern. Going to look at the Einsy schematic to see how the circuit is built and if there is something common between the items that are reported for the intermittent issues. I have spent time checking the cables and they shouldn't be broken in the few hours of printing that has happened since Prusa runs theirs 24/7
RE: Thermal issue - Over temperature but display is normal.
After some quick tests, I confirm that the thermistor is damaged and isn't linear. A bead resistor in a quick setup is about 12 degrees different but consistent across a few different settings. I am now wondering if this has been an issue for awhile since I had to lower my print temperatures to get decent prints with PETG.
On disassembly I found that my heater block is damaged from the excessive heat. Having looked that the Einsy Rambo board, there is another connection point for the thermistor, which I think would be a good idea as a safety backup. Both thermistors could be testing to be in a close range. If one is out of range in comparison, then the printer would alarm.
In my case, if I hadn't seen it and this happened during an overnight print job, it could have been a fire.
RE: Thermal issue - Over temperature but display is normal.
FWIW, I have submitted an enhancement request on github to use the third thermistor connector on the Einsy/Rambo board for a safety thermistor. I know that there are other tools available for adding safety features but it would be a selling feature to have this as part of the printer. Now I have a reason to get my OctoPrint working.
RE: Thermal issue - Over temperature but display is normal.
For those interested. Prusa was quick to send me a new, complete hotend due to the damage. Prusa also sent me a new satin sheet since they said I will never get the overheated PEGT off of the sheet. I already had all the 3D printed parts as spares so I didn't get the printed parts.
I cannot get the printer to calibrate since putting the new head on. Even pulled the printer to pieces and reassembled, still cannot get XYZ calibration to work. Dealing with Prusa now.