Troubleshooting filament sensor Mk3S  

RE: Troubleshooting filament sensor Mk3S

Check

1. the cable near the IR filament sensor.
2. that the filament path is clear of obstructions or filament debris.
3. follow the "Printer maintenance and print issues " section 13.3 Filament sensor in the 3D printing Manual for the MK3S. The latest version is here: https://www.prusa3d.com/downloads/manual/prusa3d_manual_mk3s_en.pdf

The IR sensor should report 0 instead of 1 when there is no filament detected by the FS-Lever, steel ball, and IR sensor assembly. If the sensor is stuck at 1 then you may have something stuck.

To diagnose where the issue lies:

1. power the printer off
2. take the FS-cover off the top of the extruder
3. undo the screw holding the IR sensor down
4. carefully lift the IR sensor up while it is still connected to its cable.
5. carefully put the sensor into an empty matchbox so it is in the dark.  
6. power the printer on and check the IR sensor status again 
   If the IR sensor is still 1 then the IR sensor is faulty. Try cleaning the IR sensor as per section 13.3 Filament sensor in the 3D printing Manual for a MK3S.
   Otherwise there is an issue affecting the FS-lever and Steel ball assembly for the filament sensor. Check that the FS lever is free to move and the inserted magnets repel each other. Check that the Steel ball assembly is also free to move.

RE: Troubleshooting filament sensor Mk3S

@jonathan-lin

So I removed the cover that is over the sensor, and then as I loosened the screw that holds down the sensor pcb, the sensor changed from always being high to actually being low like it's supposed to.  Also change back to high when the filament was inserted.  So right now I am leaving that screw slightly loosened, and put the cover back on.  Is there a more permanent fix?  Is this a issue with sensor or do I need to replace one of the 3d printed parts of the extruder assembly?

RE: Troubleshooting filament sensor Mk3S

Looks like your IR sensor is working but is being false triggered by the FS lever when it is being secured with its screw.

 Also read the following webpage  for troubleshooting Mk3S filament sensor issues:  https://help.prusa3d.com/en/article/ir-filament-sensor-troubleshooting-mk2-5s-mk3s_112226

We need to check that the mechanical portion of the filament sensor assembly is still clean.

Check that:

1. the Extruder assembly for warping and assembly screws that are loose or too tight. 
   Warping can affect the filament sensor mechanical alignments.
   
   Warping can be  caused by the PETG in the parts getting too hot, cables being incorrectly caught between parts of the extruder, or using the wrong mix of revision parts in the Extruder.

   Screws that are too tight or too loose can also warp the assembly due to uneven forces.

    

2. the filament path  down thru the top of the extruder body and between the steel ball and the extruder body is clear of all filament debris including filament strings. 
3. that there is no filament debris on the FS steel ball itself, within/on the FS steel ball assembly or on the FS-lever itself.
4. the IR sensor cable has a loose loop before the plugs into the IR sensor. See picture in step 22 of
   https://help.prusa3d.com/en/guide/3-e-axis-assembly_55136#56232

   This loose cable loop prevents movement of the cable from pushing the MK3S filament IR sensor out of alignment with the rest of the filament sensor assembly.

   You could slightly raise the height of the IR sensor when it is mounted by adding a very slim plastic shim washer onto the screw between the IR sensor and its place extruder body.  I'd follow the troubleshooting Mk3S filament sensor issues guide above first and only add the plastic shim washer if that is the only option.  You can 3d print your own shim washers at various thicknesses (determined by the sum of your printer's first and subsequent layer heights if any).

Hope the above also helps

RE: Troubleshooting filament sensor Mk3S

I had the same problem when I was done assembling my printer.

My solution was as follows:

1. Print this (all three parts): https://www.thingiverse.com/thing:3880394
2. Unscrew and remove the original cover
3. Unscrew the filament sensor PCB
4. Place the shims as shown in the pictue on thingiverse
5. Screw the filament sensor PCB back on
6. Screw on the newly printed cover.

The reason this works is that the filament sensor sits t0o low and thus is always triggered (state is 1) even if there is no filament loaded. Only placing the shim is not enough since the original cover does not provide enough room for the raised PCB and will push it down again. The new cover provides that little bit of extra space.

Since installing this fix my filament sensor works flawlessly.