MK3 was working great, now hot end can't get over about 180 degrees
What led up to this was clearing a filament jam and I accidentally broke one of the wires to the heater cartridge. That one is on me. I ordered a replacement off Amazon that people recommended and said used as a drop in replacement for a Mk3 (24volt, 40amp) and rewired the assembly with the replacement part. Not only did it heat up much slower than previously, it capped out around 183 before the preheat error popped up because it took too long to heat up.
My initial thought, like probably most people reading this, was that the vendor sent me a 12v heater cartridge instead. I verified the packaging, and my order, and both confirmed it was a 24 volt cartridge. I checked the resistance to make sure it was within spec, and it was 15.1 ohms. From what I've read on the Prusa forums, it should be between about 12.3 and 15.1 for a proper 24v cartridge.
At this point, I ordered an official replacement heater cartridge and thermistor from Prusa. This arrived yesterday and once again, I replaced both parts in the assembly. I measured the resistance of the new heater cartridge before I replaced it (14.1 ohms). Same results. Still takes much longer than expected to heat up and only gets to just over 180.
My next step was to verify the power supply. I have the original power supply and also a Mean Well 350watt 24v power supply. Both power supplies are outputting 24 volts as expected, and both power supplies yield the exact same results to the temperature and time it takes to get there.
Some people have suggested re-flashing the firmware. I have done this, re-flashing 3.8.0 (the latest one at the time of this writing) with no change in output. My printer is in an enclosure. I have run this inside and outside the enclosure, with and without fans. There is no difference in the output.
Someone suggested re-running the PID calibration (which I have done), but it can only get to 180 degrees. Nonetheless, I did run through this several times with no change in output.
What am I missing? I have multiple heater cartridges, thermistors, and power supplies that are all checking out as good? Is there something in the board that can cause this that I am missing? I did find another forum post from a year ago on here that seemed like they had the exact same issue, but no resolution was ever posted.
RE: MK3 was working great, now hot end can't get over about 180 degrees
does the thermister read the correct temp at room temp?
RE: MK3 was working great, now hot end can't get over about 180 degrees
@david-a66
Yes, both the original and the new one both read as expected.
RE: MK3 was working great, now hot end can't get over about 180 degrees
12v heater cartridge would have heated up way too fast, not super slow as you report.
I'm with david-a66 in suspecting the thermistor has gone bad. Their wires are fragile and the casings crush with just a little bit too enthusiastic set screw tension. However, you say the room temp reading is OK.
There is a small chance the pluggable screw terminal block that plugs into the EINSY is loose, but that would probably be accompanied with the scent of burning plastic.
Do us a favor and factory reset with erasure of all data. 3.8.0 does not clear the EEPROM properly and we've seen weird behavior of all sorts if users don't clear data.
RE: MK3 was working great, now hot end can't get over about 180 degrees
@guy-k2
OK, I did the full reset and went through that whole process with no change.
I decided to break down the whole extruder assembly and redo it to see if I missed something. As soon as I took it apart where I could see everything, I noticed the heatsink was somehow screwed all the way flush with the heater block. I took all the components apart and rebuilt the extruder following assembly guide.
It's ALIVE!!! I was able to get the temp up to 285 to hot tighten the nozzle without any further issues.
RE: MK3 was working great, now hot end can't get over about 180 degrees
Thermal short-circuited heat break.
Will have to add that to list of suspects.
RE: MK3 was working great, now hot end can't get over about 180 degrees
always something new
RE: MK3 was working great, now hot end can't get over about 180 degrees
@guy-k2
OK, I did the full reset and went through that whole process with no change.
I decided to break down the whole extruder assembly and redo it to see if I missed something. As soon as I took it apart where I could see everything, I noticed the heatsink was somehow screwed all the way flush with the heater block. I took all the components apart and rebuilt the extruder following assembly guide.
It's ALIVE!!! I was able to get the temp up to 285 to hot tighten the nozzle without any further issues.
That was the first thing I thought of when I read your issue (but didn't see it in time to help you, unfortunately). I had the same issue where I incorrectly re-assembled my hotend and the heatsink was in contact with the heater. I couldn't get my hot-end above 150C.