Anycubic Kobra S1.... Error 11512

A few days ago, one of my Anycubic Kobra S1s started displaying intermittent errors, most notably error 11512, but not all of them. After several disassemblies—Ace Pro, extruder, etc.—I was always able to get it to restart, but I wasn't sure I'd actually identified the cause. The printer had accumulated approximately 690 hours of use .

Over the next few days, during a print run with numerous color changes, the problem recurred at almost every change. I disassembled everything again, but found nothing abnormal.
At that point I decided to carefully observe the movement of each component involved, comparing what happened with another Kobra S1 that instead worked perfectly.

After about ten minutes of comparison, I narrowed down my suspicions: the 4-in-1 conveyor on the back of the printer.

I unplugged it and analyzed it with the oscilloscope: both sensors (filament presence and movement — two optical forks) showed highly unstable signals that were not related to the filament sliding.

At that point I open it.

...and surprise!

The knurled wheel that is driven by the filament rubbed internally against the brass tube .

Over time, this friction had produced a very fine conductive filing , which had coated the optical sensors, throwing them into total confusion.

I cleaned everything thoroughly, slightly widened the gear seat and, just to be safe, applied an insulating coating to the electronic components.

Once reassembled, the printer completed more than 500 filament changes in two days without a single error (except for one actual case of filament breakage).

I then opened the second Kobra S1, which had many fewer hours of use, and found traces of the same brass filings: I also carried out the preventive modification on that one.

Happy printing!