CORE ONE MMU3 not feeding through FINDA  

CORE ONE MMU3 not feeding through FINDA

I have a CORE ONE and an MMU3, both purchased assembled and both functioning fine until the last few days. During a long two-filament print, my CORE ONE reported a filament not triggering issue. I removed the relevant filament and shaped the tip, but it would not feed (loud chattering from the FINDA. The same happens now with all filament positions, so I think the jam is in the FINDA block itself.

I have checked the paths for all five filaments from the tubes through to the pulleys. All are clear. If I set the FINDA to any position, then manually rotate the shaft to move it to one side, and then press the second button on the MMU3, the filament feeds forward smoothly and silently.

It I insert filament from the front of the FINDA, the ball lifts and the red light switches off. I cannot push the filament any further from the front. I'm not sure if I should be able to.

I have tried moving the FINDA all the way to the right and blowing pressurised air through it as much as I can (and more generally from every other angle). There is no sign of anything coming out from the back.

However, it still cannot load and feed the selected filament - just loud chattering.

So, I assume there is a blockage behind the FINDA sensor and in front of where the pulley would feed the filament in.

Is there any easy way to check and clear that space? Do I need to dismantle the MMU3, or is there something else I should try first?

Many thanks, Donald