Hotend having a fluctuating temp?

From Octoprint:

I’ve been printing with MakerGeek PETG for a little over a year at 230 (the attached shows 240, one of the experiments). The Mini just turned 2 years old…it’s been a solid workhorse.

Lately, it’s been temperamental. Filament wouldn’t extrude properly, suddenly went from no stringing to stringing often. The print jobs that have been succeeding, had a straight line for the “Actual temperature” in Octoprint. The failing ones have had the jagged lines that you see in the image. (Failed jobs will either stop extruding part way through the first layer, or even at a future layer in mid air.)

The wires don’t appear to be loose. Is the variation a sign of a failing part?

Thanks for any suggestions!

That’s often a failing thermistor or heater cartridge. They are around $2.00 to replace. I’d try swapping those out first. if its not that, it could also be wire short or a connector issue of some sort, but its usually the thermistor.

Thanks for the feedback, I’ll look at learning the replacement process for a thermistor.

(And for some reason my image link wasn’t working.

Relaying information, in case it’s useful for others.

I installed a new heater cartridge. (I was going to do thermistor as well, but I think the store sent me the wrong part - a huge barrel-like thing with a couple of wires.) Didn’t know how the original thermistor wire was supposed to look, running behind the plate on the hot end…is its sleeve supposed to go trapped there? Maybe…

The first run, I smelled some burning plastic - obviously not filament. I moved around the thermistor wire’s heat shrink and broke the thin strand of thermistor wire. It looked soldered in the first place, so I resoldered it, put new heat shrink on it…put it back together.

Second run, the head crashes into the PEI sheet, drags off the back (smacking into the washers on the way out), and starts spitting out filament. I abort, z-home…and now it doesn’t move off of the z-axis. I learned about sending printer commands at this point…m119 was returning “Recv: z_min: TRIGGERED” and “Recv: z_max: TRIGGERED”. (Should return as “open”.)

At this point, I thought I needed to check the z-axis motors to see if they worked. (If you disconnect the printer head, none of the axis motors will run.) Turns out…the screws holding the NEMAs are probably loctite’d in. There are some fuses on the RAMBO board, but they didn’t appear to be tripped.

I ended up ordering a whole replacement for the hotend, to avoid the guesswork if it was still the hotend. (It turned out to be a short in the original hotend. Keeping it around, and will attempt a better repair of it if I need it again.) Nothing else needed to be fixed. I changed the nozzle size to .35mm in Cura and Octoprint. Cura did insist that it was a new printer head, and I needed to install new firmware. The developer version I was using never actually gave me feedback when I did install it correctly.

I hope this is useful to folks…highlights of what I learned:

  • Take pictures of wiring, before unscrewing the next part
  • A short doesn’t mean you’ve blown the RAMBO board or motors (whew)
  • Do not attempt to brute force the NEMA motor hex screws. (1.5mm, I think I almost broke the tool.) Maybe heat them up with a soldering iron to loosen loctite?
  • Breathe.
  • And maybe remove the nozzle from the old hotend before disassembly. Oops.

Here’s the mini extruder build instructions with pictures if you need it to fix the origional one you have