Nozzle temperature too high at start time
Hi,
I've been printed happily with my MK3 and then MK3S for five years now. Few weeks ago I started having some print failures due to nozzle temperatures dropping below the expected temperatures. I tweaked some settings and I could print with more successes but still I experienced rare failures.
Moving to the main issue, the printer is now putting itself in "Thermal anomaly" few seconds after boot time as it sees a nozzle temperature ~185°C (readings are not stable). The nozzle is cold as it had no time to heat anyway (and no command was sent to do so). Obviously I cannot launch any prints, the printer is beeping very aggressively non-stop (along with the error message on the LCD screen). I've checked the hotend thermistor with a multimeter, by removing its connector from the board, measurements seems fine:
- in very cold water readings are above 200kΩ (ice cubes added to the water)
- around 125kΩ in ambient air (~21°C in the room)
- below 80kΩ if I press it between my fingers
While taking the measurements I've moved its cable just in case there was some shorts, nothing. I've also upgraded the firmware to its latest version (v3.14.1), no difference.
When it gets interesting is starting the printer without the thermistor connected to the board does not change anything! Readings are still high and the same error / bips happen.
My conclusion is that was the board is somehow "damaged" and should be replaced but I could be missing something. Is there anything else I should check?
Thanks a lot for your help!
Photos of the readings (taken in the garage, ambiant temperature ~12°C)
RE:
Based on https://github.com/ultimachine/Einsy-Rambo/tree/1.1a/board I've measured resistors R6, R32, R31:
- Resistors R6 & R32 give 1,8kΩ instead of 2,37kΩ
- Resistor R31 gives 2,1kΩ instead of 4,7kΩ
I've also measured the resistors for the other thermistor, they give much closer values.
I'm not equipped to replace such small components on the board, I'm ordering a new board and thermistor (doesn't hurt to replace it too).
RE: Nozzle temperature too high at start time
I know that I am late to this.
First, you cannot accurately measure a resistance when it is in a circuit board. The other components will affect any reading. I have seen this mistake over my decades in electronics. Since you say you cannot change them, I am assuming that you tried to measure them while still mounted.
I would replace the thermistor and test. I had my printer thermistor fail and melt my ASA printed head. Watching PETG come out like water is not a great experience. My symptoms were high temperature, even though the reading was normal. Thermal code is designed to help prevent the issue I had. Took out my PINDA as well.
Also check that the thermistor and heating element are mounted properly. I have read that ideally you should have a high temperature heat sink compound in the mount.
RE: Nozzle temperature too high at start time
Hello Robin_13,
Thank you for your tips. I had replaced the main board before seeing your message. You're right I measured very approximatively the components mounted on the board. I also measured the same components for the other thermistors so theoretically those should have been similar to R6, R32, R31. To my surprise they were not, the measurements for the other thermistors were much closer the "official" values.
Anyway the board replacement fixed the issue even with the old thermistor mounted. So for whatever reason the board became faulty 🤔.
RE: Nozzle temperature too high at start time
Interesting to know. Thanks you for the update. Thermistors are pretty stable but when they fail, they fail in a gi