Printer freaks out suddenly during normal print

Basic Information:

Printer Model: RatRig Vcore Pro
MCU / Printerboard: Bigtreetech SKR Pro V1.2
klippy.log Unfortunately no klippy.log from that print anymore. Instead I’ve got an octoprint.log attached (I made an extract from the failed print) (1.8 KB)

I’ve been printing with my RatRig vcore for 2,5 Years now without any major issue but some weeks ago I observed a very strange behaviour: Out of a normal print it suddenly made wild movements to all directions, back and forth, hitting the frame like crazy. I immideately stopped the print with the reset button of the printer board.
I started a new print and everything went normal as for many other prints the following weeks.
But the problem occurred again - I could not explaint it at all.
Of course I checked wiring of everything but could not find any loose one.
For all the next prints I had the windows game screen recorder running since I wanted to see what’s happening just before the chaos starts again.
After several good running prints - long and short ones - I caught it on video - but that did not help. On the video one see that the printer pauses for a very short moment and than it starts to rund back and forth as described.
I’ve got the impression, that those movements are not just accidentally, but rather a motion based on a much too big feedforward constant.
As I wrote above I don’t have the klippy.log anymore. On the pi there isonly one for the last print and one for the next. Maybe 2,5 years ago the backup for the klippy.log was only for one file? (to be honest, until last monday I did not even know that such files exist. Somebody from gave me hints about those files and also recommended to post my problem here).
One thing I’m really wondering about: in the octoprint.log you see that there are many “lost communicaiton with MCU” - errors, in a very very quick order. I don’t understand, why klipper does not stop the print if something like that happens. Or is it just a matter of a certain parameter I have to set in order to have klipper stop the print the very first time a “lost communication” occurs?
Thanks in advance for your help!!

Hello @Tommy !

How did that happen?

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That is what WinSCP shows me on the /tmp folder.
no other log-files.
I would need a klippy.log.2023-09-23 - but there is no such file.
How this happend I don’t know. Since I don’t know how klipper normally handles those files.

You tried this one?


klippy.log (3.7 MB)
It seems it is from the current print (I have the printer printing for 2h15min now)
I attached it anyway.

The current session is named klippy.log and the backups/older ones have the date in it.

Hello everybody,
just some minutes ago the malfunction happened again, after many hours of well going print jobs today.
And this time, I can attach the klippy.log.
I very much hope, that this thread still finds somebody who can have a look at it and hopefully finds out the reason for the malfunction.
Thank you all very much in advance!!

klippy.log (3.0 MB)

Your error is:

Timeout with MCU 'mcu' (eventtime=6493.810291)
Transition to shutdown state: Lost communication with MCU 'mcu'

See Timeout with MCU / Lost communication with MCU
Since this is an intermittent issue, it is unfortunately difficult to diagnose, but so far it has always been traced back to some sort of hardware instability.

Thank you Sineos,
I have already replace the Pi, the SD-Card, the USB-Cable and the power supply of the Pi.
I checked all the cabeling - no bad one detected so far.
24V under load condition is ok (24.1V).
Heater for bed is externally supplied (230V) as well as the HotEnd Heater (12V-Power supply).

So, in my opinion the left device is the SKR-Board or the 24V power supply which is similar to a laptop power supply but with an output of 24V. It probably does not have buffer capacitors in it, so even short mains flicker would lead to an undervoltage to the board. Hopefully I will be able to monitor the power supply soon with a voltage monitoring system (could record in 1ms cycle).

If it turns out that the power supply is ok, would it also be possible that the board could create such a malfunction (in this sporadic manner)? I mean, it was working flawless for the last 2 1/2 years - I haven’t changed anything on the complete printer setup.

Thanks again!

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