Z-Homing while bed is heating causes lost communication with MCU

Basic Information:

Printer Model: Wanhao Duplicator i3 v2.1
MCU / Printerboard: SKR Mini E3 v2.0 / Raspberry Pi 3B+ (connected via USB)
klippy.log

moonraker.log (7.8 KB)
klippy.log (38.0 KB)

Describe your issue:

This is a strange one. I was originally running Marlin / Octoprint with no issues at all, and I was able to complete all of the config verification for Klipper after flashing it on my SKR. The only issue I’m running into now is that the MCU disconnects from my Pi if I run a homing procedure while the bed is heating - it specifically happens after the X / Y homing has completed and while the Z-homing (via BLTouch) is occurring.

I don’t think it’s a PSU issue as I had no problems with my Marlin install, and I also double checked all board connections. I’ve also tried multiple different power supplies for my Pi and nothing changed.

Any ideas? I’m stumped.

Hello @novaterrus !

Have you tried homing Z before heating?

I have, and it does work as long as the bed is not actively heating.

I recommend homing before doing anything else.

Homing is a precision process and cannot be interrupted by other things like polling the thermistors. That is also the reason why 2 or 3 axes can’t be homed at the same time.

It works as this:

  1. Send a step towards the endstop switch
  2. Is the switch triggered?
  3. No → Goto 1. Yes → exit loop

While I think that’s great advice in general, in particular in regards to homing the X and Y axes, homing the Z-axis while the bed is cold is inaccurate due to thermal expansion. In particular I’m trying to be able to run ABL while the bed is at temp.

It appears, you have your start gcode in the slicer.

Can you share it?

No start gcode involved at this point aside from manually sending SET_HEATER_TEMPERATURE HEATER=heater_bed TARGET=55, M106 S255, and G28. All commands are being triggered via the Mainsail UI.

Ok, I’ve done more testing and it appears that this is an issue with the PSU. As long as I keep heating power for the bed below 15% it will successfully allow a Z-home.

Time to dust off one of my old ATX supplies…

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