MakerFarm 8" i3v Prusa build by Printbus

[printbus]

GARBAGE DATA ON LCD DISPLAY
The LCD screen has frequently been displaying garbled data. Initially this was when I was trying to do something with the rotary encoder. I thought static was perhaps being passed through the metal knob I had on the encoder, but I still saw the display get messed up at random during prints after replacing the knob with a plastic one.



I've written microcontroller software for similar displays before. For those that don't know, with these displays characters can be displayed from an ASCII character set, an alternate character set, or a number of user defined character bitmaps. While the specifics of the alternate character set vary by manufacturer, some of the characters I see on my screen are typically found in the alternate character set. I'm not sure how data from the alternate character set is being written to the LCD, but others with the Marlin-type display have reported the problem often is noise coupling into the LCD ribbon cables. My ribbon cables were touching the X carriage cable harness passing over the top of the printer. I drilled a few holes in the right side of the frame and added a zip tie to pull the ribbon cables away from the X carriage harness. Looking good so far, although I've only ran one two hour print job since the mod. Next time I'm ordering from the likes of Mouser or Digikey, I'll likely order new connectors for the ribbon cables and shorten them up, which others have also reported as an occasional fix.



FOLLOWUP COMMENT #1: Moving the ribbon cables has definitely helped. There still is a sensitivity, however, to fingers reaching over the top of the frame and touching the LCD circuit board when reaching for the knob.

FOLLOWUP COMMENT #2: After a few months, I got around to building new, shorter ribbon cables. I'm not sure that made any difference. An explanation on what is happening that results in the garbled display is discussed in the Garbled LCD Screens thread in the Firmware Enhancements to Marlin area.

FOLLOWUP COMMENT #3: Looking into the firmware associated with the LCD panel, I grew to realize that the existing firmware base has a built-in provision for restoring the display once it gets into this garbled mode. Assuming the printer isn't busy printing from the SD card, insertion or removal of the SD card will restore the display to proper operation.

FOLLOWUP COMMENT #4: Newer versions of Marlin have yet another built-in recovery scheme. When the printer is at the top status screen, pressing in on the panel button will also restore the display.

FOLLOWUP COMMENT #5: I'm still getting the garbled display a lot. While it does usually happen when I touch the display, I have seen the display garbled during a print when I haven't been close to touching the printer.