I’d guess that this error is related to a thermistor or thermistor wiring issue. I believe at room temperature, the thermistor should have a resistance of approximately 100 ohms and, of course, the wiring between the tool head and the controller board needs to be intact.
A little troubleshooting with a multimeter should confirm my suspicions.
Thanks again. I’ll do some more probing and inspection this afternoon. There is a thermistor on both the tool head and the print plate, correct? Even if the printer never works, I have some students working with me as we troubleshoot various parts of the system and we are learning a lot in the process!
Yes, there is a thermistor on both the tool head and the print plate. You would have to check the OHAI documentation to determine if they are the same type.
However, the probability of a thermistor failure is much lower than the probability of a broken wire between the thermistor and the controller board.
BTW, the OHAI documentation for your Mini 1 (use the serial number to determine which model) should also contain pinouts for the tool head connector. You should also be able to find controller board diagrams as well.
OK, I did a continuity check on the wires going from both the bed thermistor and the tool head thermistor to the board and everything checked out. I checked the resistance on the bed thermistor and it was 118. When I checked the tool head thermistor, I just got an OL reading on my Fluke Multimeter. It appears that I have a bad thermistor on the tool head. If someone agrees with this assessment, I will start looking for a replacement hotend.
I agree with your assessment but you shouldn’t need a replacement hotend, the thermistor can be replaced.
If you feel like that is a task you don’t want to take on, I’d guess that you could send the tool head to LulzBot or IT-Works 3D and get it repaired for less than the cost of a new tool head (which is what I assume you meant when you said replacement hotend).
As I was researching a possible repair, I came across this (OHAI: Open Hardware Assembly Instructions) which seems to indicate that I can replace the hot end without replacing the entire tool head. Are you saying that there is a possibility of just buying the thermistor by itself without even having to buy a new hot end? If that is a possibility, I feel fairly confident that I could take on that repair myself. Let me know if you happen to have a link to the specific part that I would need. Thanks.
You should be able to replace the thermistor. I believe it is an EPCOS 100K.
Here is a decent set of instructions.
You can also contact the support folks at the links in my previous post and ask them if they sell the thermistor or can verify that the part I posted is the correct one.