Hotend temperature issues
Hi,
The problem:
Our i3 MK3S is constantly reporting MINTEMP and does not allow printing. The temperature of the hotend is shown to be 14 °C, while the heatbed is showing 24 °C. When we manually heat the hot-end by hand so that it shows 16 °C, MINTEMP disappears and the printer prints, but with significantly worse quality than before.
What we tried:
We tried everything in this guide https://help.prusa3d.com/article/am4dykf2rw-mintemp to no avail.
We also measured the thermistor with a multimeter and measured 400 kOhm (instead of 100 kOhm mentioned in the article), but we don't know if this is a problem, since the value is not infinity like it probably would be if the thermistor is shot (after all, it shows the 14 °C, not 0 °C).
We also tried to update the firmware from 3.7.1 to 3.7.2, but the temperature did not change, but it was no longer possible to enter the main menu (single click on the main button did not do anything). So we downgraded back to 3.7.1 and the situation is still the same.
I would be grateful for any ideas. Thanks!
(I'm also not sure if this is the correct place to post this, so I'm sorry if this is in an incorrect place.)
RE: Hotend temperature issues
I wouldn't be so quick to discount the problem is not with the thermistor. The 400K Ohm vs expected 100K could well be the problem. Since you are not seeing 0 degrees there is continuity. For fun, did you run a PID calibration?
If you manually run the hot end up to temp and it prints, but as you say with poor print quality, the thermistor may be sending an erroneous value. For grins, did you try to print something like a calibration tower? That might provide some insights as to the thermal stability, and a rough indication as to the actual hot end temperature.
RE: Hotend temperature issues
I second the thermistor -- if it shows 400k at room temp of 25c it has failed. Period, end of discussion. The value should be within a couple percent of these (allowing for common el-cheapo meter inaccuracies, even 5% is okay). But >5% off is a fail.
ps: thermistors fail by going high resistance sue to decomposition of the resistive material.
RE: Hotend temperature issues
RE: Hotend temperature issues
Alright, thank you both @tim-m30 and @joseph-r12, I have ordered a replacement thermistor from E3D (together with a few other parts of the hot-end which are now dirty to an embarrassing degree) and I will report back once we try to replace it.
@joseph-r12 We ran PID calibration and it did not help. We didn't print a calibration tower specifically, but we re-printed some quick prints which we had from the same printer and the same plastic from before the issues to compare. There was significantly more stringing with PLA and the extrusion seemed inconsistent, even during the first layer, there was sometimes too much material and sometimes tiny gaps. However, since we also made the upgrade from MK3 -> MK3S, we are not sure if this could be the reason, at least more so than the temperature issues.
RE: Hotend temperature issues
I just finished my MK3 to MK3S upgrade. After the upgrade the hot end fan faulted and I had to do a factory reset. Long story short, I ended up replacing my hot end with a new one from Prusa. And now I need to complete dialing it in. The upgrade was more expensive than advertised 🙂 Good luck on replacing the thermistor.
Tim-m30, thanks for the resistance/temp table. Nice to meet another electronics guy. Cases and nonsuch for electronics/radio is why I got into 3D printing.