[Solved] Stuck inside the Filament Sensor - or how I learned to bin my old filament  

Stuck inside the Filament Sensor - or how I learned to bin my old filament

TLDR Don't use really old filament!!

How to disassemble the filament sensor and side to clear broken filament.

Hit my first problem with the Core One yesterday, an old PLA filament I'd been using got stuck and wouldn't unload, I couldn't push it through from the sensor side, nor could I push it back from the detached hotend side. Something was definitely borked.

I'd resigned myself to having to disassemble the side and sensor to get to the bottom of what had gone wrong, thankfully the Core One Kit Assembly Instructions (link) are online so that helped massively with reducing the fear of taking the side apart.

After removing the PFTE tube from the hotend by wiggling the cover at the end of the tube up and pushing down on the bowden coupler to release the tube (taking care to support the hotend as I did so) I moved to the side panel. This was straight forward popping out the plastic connectors from inside the unit, this can be made easier on your fingertips if you have a small hard surface to push with, a metal thimble worked great for this. I removed the metal side and the plastic window, and all but the bottom three connectors were accessible from the inside, for the bottom ones I was able to work them out with my fingernails.

With the top window put to one side I switched to removing the metal side panel, this is screwed through the frame and into the filament sensor itself so you'll have to unscrew it, I used my iFixit driver with a Torx T8H bit to unscrew both screws in the orange handle from the outside, you should be careful not to strip the screws so use constant and careful force. The handle can now be removed and the side panel can be carefully removed, taking care not to pull the filament sensor unit from the inside with it.

With the Filament sensor exposed my first thought was to remove the PFTE tube but I couldn't figure out how to remove it from the collet, so instead disassembled it in place, this turned out to be absolutely fine and I'd do it this way again in future.

When removing the cover of the filament sensor be very careful to make sure the small ball bearing inside doesn't pop out and get lost, when I took the cover off the magnet on the arm popped off taking it with it, but I was able to keep a hold of it easily.

With the top off I could now see the problem, the filament had broken inside the sensor just before the point it exits to the outside via the small PFTE tube, it had kinked up and was wedged against the inside of the sensor.

I was able to extract it using a pin to dislodge it and then the pliers that came with the Core One to pull it out.
With that now cleared, I pushed a length of good filament through the system starting from the disconnected hot end side, clearing the other broken bits from the tube.

Reassembling the sensor unit as described in the assembley guide was then also straight forward.

Adding the side back and attaching the sensor was a bit more complicated, I'd left the short bit of PFTE tube from the handle attached (as I couldn't remove it, more on that in a bit) and had been trying to slide the sensor back into place over that tube with no success. I then realised that the collets are one way so rather than pull from the handle side out I was able to easily pull the short PFTE tube out from the internal side of the handle.

With that done fitting the handle and sensor was easy again following the assembly instructions. Finally re-inserting the short PFTE tube, adding the plastic connectors to the side panel and window, and I was done.

To be cautious, I ran a calibration again, no issues, before printing a test benchy and the printer was back in action... panic averted !!!

All in all, a pretty straight forward process, much easier than I'd been worried it might, the kit assembly instructions being the life saver though I'd not have felt comfortable attempting it without them.

So if you ever hit a similar problem, I hope this helps, you'll be able to service the filament sensor/PFTE tube very easily should you need to.

The one suggestion I would make would be with the use of the collets, they do seem to be impossible to remove, so should you ever have to replace the PFTE tube internally you might be in trouble, it would be much better if an actual connector was used that could make removing the tube the same as the hotend side.