PID autotune fail on Marlin?

I’m running Marlin on an SKR mini e3 v1.2, at 24V, with a hexagon-style hotend. I was printing with it yesterday and this morning, but after a spaghetti mess this morning, I’m getting overshoot and oscillation on extruder temperatures.

Despite multiple PID autotuning cycles, the hotend is not stabilizing enough to start a print. I’m not sure what changed. For a setpoint at 205⁰, I’m watching it bounce between 199⁰ and 216⁰. This makes me think that the PID autotuning cycle isn’t finding the right values — but also I watched the temperatures during the auto-tuning cycle and they stabilized. I’ve never had this problem before.

I’ve tried changing the PID values manually following suggestions at for this problem, but I’m not seeing any change in thermal cycling behavior.

Any ideas what I could check?

As so often happens when investigating something unusual, the question turns from “why doesn’t this work?” to “how did this ever work?”

I had, it turned out, changed PID_FUNCTIONAL_RANGE from 10 to 2 which naturally made it inclined to overshoot the range. I did that when experimenting with settings while worrying about cycling the SSR too much, and lost track of the fact that I had changed it. Setting that back to 10 resolved the issue. I might increase it a little further, in fact, because it heats so quickly.


Been there. This is usually when I restore default settings (or similar), or start taking a real close look at a diff. It is usually followed by me slapping my forehead. :man_facepalming:

1 Like

I usually comment out the original setting and write the new setting directly below it. Can see at a glance what the default was previously that way.

1 Like

I’m used to just using git diff.

I was starting from the stock e3 mini configuration, which conflated board-specific changes with specific settings for the ender 3. Because I wanted to keep those specifics out of history, I didn’t check in that version; my first mistake. That made my changes buried in the diff. Silly mistake and I know better.