Intermittant EOF / MCU timeout failure with Kingroon KP5L

I’m at my wits end with these intermittent print failures on the kingroon KP5L. Here’s the relevant section of log: Stats 1854.7: gcodein=0 mcu: mcu_awake=0.007 mcu_task_avg=0.000023 mcu_task_stdd -

It can happen at any point, but usually early in the print. With the same gcode, I’ve had it happen at various points in the first 5 layers, but occasionally it gets into the 20s. Once it printed about a hundred layers before crapping out.

The failure always starts in the log with a “Got EOF when reading from device”. The printer will freeze, and klipper will display “lost communication with MCU” or something to that effect. Hitting firmware restart twice re-establishes communication with the printer. Once never does it, twice always does.

At this point I have swapped out the power supply, USB cable, microSD card, and RPi. Is the printer board itself causing the issue? I only had the printer for a couple weeks before converting it to klipper, but it seemed fine in that time. I completed a couple 10hr+ prints with the stock FW, so I don’t think the board is physically faulty. Conversely, I have occasionally had prints complete since converting to klipper. Not often, but it has happened.

Is there anything else I can try?

Please just attach your full and unmodified klippy.log showing the issue. (520.6 KB)

Full log attached.

Here’s the load graph and some info generated by

klippy.log.config0001.cfg (3.9 KB)
klippy.log.shutdown28572.log (5.8 KB)

Nothing really telling that I could see. Sorry, no further advice. If you had not changed already, my suspect would have been a flaky SD card

Yeah, I tried a new SD card. I also swapped in the known-good RPi, USB cable, and power supply from my other printer. The only thing that I haven’t changed out is the control board. There’s no way the manufacturer would warranty the board based on a problem that only manifests itself when using a non-approved FW, so either I hopefully track down a software issue, or I have to flash it back to stock.

I may have solved the problem. After trying several suggestions from other forums, it seems reducing the serial port speed from 250kbps down to 115.2kbps did the trick. I just completed a 7hr print, so fingers crossed everything stays working.

How do you change that serial speed?

Do you desloder the jumper on your main board printer to change UART mode?