I got a Lost communication with MCU error twice in a row, using the same gcode file, at around 20-40% of the print.
Longer print times have worked out fine for the last couple of days.
The printer is sitting in an Ikea Lack enclosure, with duct tape sealing and with a hotend temp of 260C and bed temp of 110C, while ambient temp is 35C.
I have several ender 3’s with SKR E3 V3 boards and I’ve had quite a few issues with the lost communication errors. For me it’s always turned out to be either the USB cable or connection of the micro USB end to the board. There was never anything indicated in the logs that gave any hints, it was just unreliable cables or a loose connection to the micro USB socket on the SKR.
It happened again about two weeks ago with a brand new cable during several longer prints, which was suggestive that cable had worked loose from the socket. So I let it sit without trying to print anything and after a few hours it happened again. So it hadn’t worked loose, it was just an unreliable cable.
I’m not really impressed with the micro USB socket on the E3 V3 it’s the only thing that’s really lacking in the design. They should revise the board and put a USB C socket on it.
Admittedly I’m using a several years old 2m cable; I’ll try with the one that looks and feels more reliable.
Would it be possible to avoid using the micro usb port entirely? Looking at the pinout[1] I see two pins labeled SW_USB but I think they might be for a jumper to enable powering the board via usb, and not the D+ and D- of the usb port itself.
You are correct the “SW_USB” pins are for placing a jumper on the VUSB line so that the USB host can power the board (when the board is running with the regular power supply these pins are left floating).
If you’re unsure about the cable, just replace it. You should be able to find a new USB-A to USB micro cable for five bucks or less.