I started a 3d print running from Octoprint, as I often do, and after 30 minutes of printing, the printer halted.
Octoprint had tried to send messages a number of times and they went unacknowledged. I didn't have the serial.log enabled, so that was all the information that I got. I enabled the serial.log and tried 3d printing again. Thirty minutes later, the Creality Ender 3 Pro halted and there was a notification on Octoprint of too many communications timeouts.
At least this time I had a log file. I scanned the log file and found six failed attempts to communicate. No other helpful information was in the file. Now what?
I came across an odd recommendation suggesting that it could be the Ender 3 LCD cable position causing communications issues. I moved the cable and tried 3d printing again. A 2 hour print ran successfully! Problem solved! Not quite.
My next 3d print, 3.5 hours long, failed after 2.5 hours. Same issue, too many failed communications attempts.
I tried a new USB cable. I tried using a different microUSB card. I tried using a different USB port on the Raspberry Pi 4 running Octoprint. I tried uninstalling and reinstalling the serial port driver. I tried a whole new install of Octoprint.
It must be the Raspberry Pi 4, it does run a bit warm. Nope, it wasn't the Raspberry Pi 4. That left only the Creality Ender 3 Pro as the culprit.
I checked wire connections and especially ground connections on my Ender 3 Pro. I even considered making my own noise shielding with aluminum foil wrapped around the LCD cable and grounded but fortunately, I tried something on a whim first.
I removed the 3d printed plastic cover for the back of the LCD that I'd 3d printed 2.5 years ago.
As I began to remove the screws that held the cover to the back of the LCD, I noticed that one screw was very loose and the other three srews were not much better. Oh well, cover removed and LCD screws tightened down, I ran a 7 hour 3d print. Because I was tired of wasting filament, I ran the Ender 3 Pro dry. No filament. I used the same settings as always but I wasn't wasting any more plastic.
It worked!
I examined the back of the LCD a little more closely and realized that the LCD ground connection to the frame was dependent on those 4 mounting screws. Loose screws could jiggle and create a ground make/break cycle that could worsen with vibration.
I got rid of that LCD back cover. I may find or make another one that doesn't use the LCD PCB screws for mounting. Then again, maybe not.
If you're having communications trouble with Octoprint to your 3d printer, always check every single ground connection and path. It never occurred to me that grounding to the LCD could affect serial communications, but only because I haven't looked at that area of the printer for over 2 years.
