PINDA NA and Selector motor hot  

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bruce.b6
(@bruce-b6)
Active Member

My multimaterial prints frequently stop with an MMU2S error (flashing red light) when changing filaments. When I set the FINDA (following https://www.help.prusa3d.com/en/article/finda-setup-and-troubleshooting_2250 ), I can check that the values are either 0 or 1, but if I leave the sensor display open while printing, it frequently shows FINDA value as NA. I have checked all wiring connections. I am unable to replicate this NA when not printing so am not sure if this indicates a faulty sensor - should I replace the FINDA sensor?

I have also noted that the idler motor (the motor by itself) gets very hot to the touch, even when printing with one filament for a long time. I have tried loosening the MMU2S tension screws to the point where they do not feed filament reliably but the motor still gets very hot. Much hotter than any of the other motors.

I recently updated to the latest firmware and don't recall either of these issues prior to the update but honestly its been a while since I used the printer as we have been moving. 

Posted : 18/08/2020 2:28 am
etienne.clement
(@etienne-clement)
New Member

Hello,

I don't have an answer to the problem but I think I have the same problem and might be able to add some knowledge.
When testing I see the 0/1 switch on the FINDA but at times I have observed the switch to NA randomly. The interesting part is that on 2 occasions the switch happened as soon as I launched a print whether the filament selection cart had to move or not. At that no filament was loaded in the hot-end. I have also checked the wiring and found at least no visual issues.
Loading "manually" seems to work and keeps the FINDA working afterwards for some time but it can't be a permanent solution.

Cheers.

Posted : 21/08/2020 12:51 pm
etienne.clement
(@etienne-clement)
New Member

During a print I observed something strange, the FINDA sensor goes to NA when unloading the filament confirming there are no bad contacts because the cart does not move yet at that time. After loading the new filament then the FINDA appears again with the right value (1). At that time the motor on the mmu2s rotates at "high" speed, this could suggest some noise or power spike issue which somehow disables the FINDA.

This post was modified 2 months ago by etienne.clement
Posted : 21/08/2020 1:33 pm
bruce.b6
(@bruce-b6)
Active Member

Thanks for the confirmation that it’s not just me. I’ve ordered a new FINDA and will see if that helps make multimaterial prints more reliable. I’ll post an update when I receive it and run some prints. 

Posted : 21/08/2020 2:30 pm
bruce.b6
(@bruce-b6)
Active Member

Replaced the FINDA sensor and it made no difference. I’ve also checked all the connectors. I still get the FINDA sensor NA reading while printing. Not sure what I will try next. 

Posted : 28/08/2020 12:30 am
krisifleming
(@krisifleming)
New Member

Hello There, I have the same problem.

I can test the Finda working fine while not printing.

Once I start Printing the the MK3S works fine until it tries to load filament.

Once the MMU2S starts the Finda sensor goes to N/A on the sensor info screen. MMU fails to load 3 times and stops.

Cancel print and Finda starts working again.

Any Ideas?

Posted : 19/10/2020 12:29 pm
bruce.b6
(@bruce-b6)
Active Member

As best I can tell the FINDA reads N/A at some points by design, or to put it differently the firmware does not update the FINDA status at all times so the display sometimes reads N/A regardless of the actual status. I found that often the issue is with the IR sensor, not the FINDA. The MMU tries to load but if the IR sensor doesn't detect the filament arriving at the extruder body, then it fails. Double check your IR sensor adjustment following the steps in the assembly manual and see if that helps.

I made two minor modifications that seem to have improved reliability for me:

    1. I printed a modified IR sensor mount that enables more precise adjustment ( https://www.thingiverse.com/thing:4609788) and that seems to have helped.

    2. I also used a variation of daniel_karlsson's design to use a magnet to help reset the ball bearing in the FINDA ( https://www.thingiverse.com/thing:3688458). I'm not sure if it helped, but figured it couldn't hurt.

With these two changes I would estimate that less than 1 in 100 loads do I get the 'MMU load failed' error.

Posted : 20/10/2020 11:43 pm
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