USB flash drive format and skipped print lines
Just a few observations of mine for those who experience either USB flash drive not being recognized by Prusa XL or skipped print lines (non replicable, random occurrence of skipped lines).
Right on day one, I swapped my original Prusa USB stick for a much smaller one by Samsung which is way shorter (to mitigate the danger of accidentally ripping out the USB drive and damaging the control interface). Somehow I managed to format it as exFat instead of officially supported FAT32, drive is 64GB so the system probably deemed exFat is better for me than FAT32 (???). Until the recent firmware upgrade to XL_firmware_6.2.5.bbf I had absolutely no trouble and everything worked fine. It was only after the said firmware upgrade to XL_firmware_6.2.5.bbf when problems started to occur.
My prints randomly started to suffer from skipped lines. Typically well into the print progress (say 75% progress and more). At first, it mislead me to think my nozzle was clogged but even after a few thorough cleaning and cold pulls the problem persisted. Then I found on this forum similar print problems related to wrong USB format and also to possibility of problematic bgcode transfer to USB stick via Connect, esp. for very large bgcode file sizes and also reported issues with memory management related to large gcode files.
In my case, I found out my prints always came out ok up to gcode file size of about 20MB. Anything bigger started to randomly demonstrate skipped lines.
Specifically, when I printed just 1 instance of my model, the bgcode was 3.9MB big and print finished always absolutely ok. The same applies for prints with 2 instances (8MB), 3 instances (12MB) up to 5 instances with a file size around 20MB - this is a breaking point. Skipped lines appeared always with 9 instances (34MB) up to 15 instances (60MB). I repeat, this skipped line problem popped out only after the firmware upgrade to currently latest version 6.2.5, until then I printed without any problems. The memory management problem in combination with my wrong USB stick format triggered the issue on my machine.
In a nutshell, my solution was:
1 - format USB drive properly as (and only as!!!) FAT32, Primary partition and set to Active - this condition is often not mentioned! If not set to Primary and Active, you won't see the USB in XL printer (same applies to other Prusa models too). I used MiniTool Partition Free for formatting the USB stick.
2 - bypass large bgcode uploads to USB stick via Connect and transfer the files locally from your computer via USB port. Nuisance, I know, but for good measure I am going to stick to this habit for a while.
3 - please be aware the skipped line problem may show up depending on your current firmware version and other related circumstances, in some combination of events can stay dormant but it is still there waiting for it's chance.
Please follow carefully the USB flash drive specs and follow them to the smallest detail - may save you some head scratching and ruined prints 🙂
Suggestion to Prusa: please consider building in USB FORMAT function into the printer firmware/menu. This would help users 100% properly format USBs.