Printer has been running fine, now I'm getting 'Lost communication with MCU 'mcu' out of nowhere

General Discussion
1

Basic Information:

Printer Model: Ender 3 V2
MCU / Printerboard: Skr Mini e3 v3/Ebb36 v1.2
Host / SBC Btt Pi v1.2
klippy.log

klippy.zip (1.2 MB)

Fill out above information and in all cases attach your klippy.log file (use zip to compress it, if too big). Pasting your printer.cfg is not needed
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Describe your issue

Everything has been working fine up until this morning and out of the blue I started getting these errors.

I started getting two errors this morning, “MCU ‘mcu’ shutdown: Missed scheduling of next digital out event’” AND “MCU 'CB1 configured for 50Mhz but running at 49Mhz!” I could get everything to start up, but as soon as I turned on the bed heater it would throw the first error, then upon restart the error about the CB1 Mhz.

Did some digging and figured maybe my USB cable had gone bad as there was a bit of strain on it at an odd angle.

After replacing the USB cable between the pi and mcu, everything seemed to working fine again at first. Until it eventually crashed mid print with ““Lost communication with MCU ‘mcu”. So now it is throwing this error randomly, sometimes a minute or two after start-up, sometimes mid-print.

I have no idea what is going on. Also of note, there was a ton of updates this morning in mainsail, that I ran after this started happening, figuring something may have changed, and then two more a few hour later. Most, over 200 packages, were for OS, then 3 for klipper screen. I keep everything up to date, so I can’t imagine these were very old.

2

The correlation between the bed heater makes me wonder about your Power supply and high current connections at the mainboard,

Put a voltmeter across your power supply and start heating a cold bed. Does the voltage sag?

Your shutdowns appear to me to be coming FROM the EBB because it can’t reach the main MCU. Low volts to the mainboard could be the problem.

3

I’ll check that for sure, I was already thinking maybe the power supply is overwhelmed since the BTT pi is powered by a 5v rasberri pi plug.

I also wound up finding something in here and changed the scaling governor from ondemand to performance on the pi. MCU behavior is continuing, but changed slightly. Tried a bunch of different usb calbes. Had AI look through my klippy logs after each shutdown, because its all foreign to me, and it seems the error is in the usb communication? Possibly noise from my U2C and it’s power wires?

4

Got it figured out. The power lines were messing with the USB cable from my PI to my mainboard and causing interference, which caused the error. I added a USB isolator to the line and it is working properly now.