Klipper "Lost connection to MCU" when starting print

[final eagle]

Hello,

Recently (after adding a surge protector and extension cable to my ender-3) I'm getting a "Lost connection to MCU" error sometimes when I start a print or unpause one. I have 2 boards in my printer: an SKR mini e3 v3.0 and the default Creality Melzi board, both hooked up independently directly to the PSU and connected via USB cable to the pi, which is in a custom case under the LCD screen.

The Melzi board is the one that keeps disconnecting.

Usually all I have to do to fix this is to unplug and replug the USB cable to the raspberry pi, and restart the pi and printer. However, recently the pi has been disconnecting from the wifi as well as disconnecting from the MCU so I'm having a hard time accessing it from the web interface.

I'd really appreciate some help on this, since it is ruining some of my prints where I need to pause and unpause in the middle!

[calm adder]

AI Help

It sounds like you may be experiencing some connectivity issues between the Raspberry Pi, the boards, and the network. Here are a few troubleshooting steps you can try:

1. Ensure that all connections are secure and there are no loose wires or connections on both the Melzi board and the Raspberry Pi.
2. Check the power supply to the Pi and boards to ensure they are getting a stable power supply.
3. Try using a different USB cable to connect the Raspberry Pi to the Melzi board to rule out any issues with the cable itself.
4. Make sure the firmware on both boards is up to date to avoid any potential software conflicts.
5. If possible, try testing the setup with just one board connected at a time to see if the issue persists with either board individually.
6. Consider checking the network settings on the Raspberry Pi to ensure it is properly connected to the WiFi network.

If the issue continues, you may want to reach out to the manufacturer of the boards or seek further assistance fro...

WARNING: This response is AI generated and may contain errors.

[final eagle]

It seems to be happening mainly when I print with PETG (240 hotend and 70 bed), although I cant confirm this completely since I havent done a lot of PLA printing recently.

The next thing I'm going to try is swapping out the USB cable and see if that solved the issue.

[devout sphinx]

Try the FIRMWARE_RESTART command in the terminal, I have to hit it every time after booting

[wraith pelican]

It also can be due to bad usb cables

[final eagle]

After it loses connection I do that and it fixes it, but then sometimes on even the next print starting it disconnects again.

However, I swapped the USB cable and it seems like the print that I'm running might be working (I probably should have done that before posting here, but oh well) so I'm going to probably let this post close and if I keep having the issue I'll reopen it

the old USB cable was working fine for a long time before this started happening though, so is it possible the printer setup was slowly ruining it? That doesnt seem right to me but wanted to ask and see if anybody had input

[wraith pelican]

I've read that some cables causes issues, specially at startup

sadly, not all cables are compilant (in fact, the vast majority ain't)

[final eagle]

Well, it just happened again (this time at 91% in the print), even with the new USB cable. I really have no idea what is happening now

One thing I thing I'm going to try is putting a piece of electrical tape on the power pin of the USB cable and see if that fixes the issue (so that it runs data only).

Taping the 5v pin didn't help

[final eagle]

So I disconnected the second Melzi mainboard and removed it from the printer.cfg and I got a successful print out, so I'm thinking so far its a problem with the board itself or the USB port on it. Its fine if that is the problem since its the secondary board though