MK3S MMU 2.0S does not load filament the second time
Short Story. MMU 2.0s was working ok at one point but now it will not load a filament the second time. It drives it down to the extruder and drive it back up and does this twice and gives up. I have adjusted the IR sensor with a 1.5mm wrent (multiple times). Tried a new flag and extruder body (the one with the hold in the left side so you can see what is going on). I don't know what is going on.
Thank you for your help in advance.
RE: MK3S MMU 2.0S does not load filament the second time
This sounds like a sensor problem. Check that both sensors (IR and FINDA) are working correctly. I've found that the FINDA is prone to getting debris caught in/around the sensor causing false readings, so it may be helpful to push a scrap bit of filament through the MMU backwards to try to dislodge anything that might be stuck in there.
RE: MK3S MMU 2.0S does not load filament the second time
This sounds like a sensor problem. Check that both sensors (IR and FINDA) are working correctly. I've found that the FINDA is prone to getting debris caught in/around the sensor causing false readings, so it may be helpful to push a scrap bit of filament through the MMU backwards to try to dislodge anything that might be stuck in there.
I tried cleaning it out. Same thing. This problem is kicking my butt. I just don't know. I may have to contact Prusa Support and see what they have to say. I have been reading though as much stuff as possible and their advice and nothing seems to help. I don't know where things when so wrong. I printed out about half a dozen prints without this issue then this started happening.
RE: MK3S MMU 2.0S does not load filament the second time
i suspect your IR sensor is not stable . it may be changing state as the tip of the filament goes by the bondtechs and toggling on and off. the filament readout on the display may not be fast enough to catch the problem. you may be able to watch the output pin with a meter to make sure it's stable during a load
RE: MK3S MMU 2.0S does not load filament the second time
I will give that a try. I will report back. 25+ years experience as a field engineer here.
RE: MK3S MMU 2.0S does not load filament the second time
i suspect your IR sensor is not stable . it may be changing state as the tip of the filament goes by the bondtechs and toggling on and off. the filament readout on the display may not be fast enough to catch the problem. you may be able to watch the output pin with a meter to make sure it's stable during a load
I don't think that is it. It still goes now and I hear a grinding noise and then it goes back up. I will always load a fresh cut filament but will not load a filament that has is not perfect. I have had them apart many times and have aligned the sensor, gears, new PTFE tubing etc and still cannot get it to work right. Very frustrating.
RE: MK3S MMU 2.0S does not load filament the second time
Take your extruder idler door off and peek into the hole where the idle gear shaft sits. You problem sounds just like mine and was caused by the shaft sinking into it's seat and causing the sensor to be flaky. It would trigger but then flicker on and off while printing. I strongly suggest the following mod as it was very helpful in cluing me into what was happening for me (saw it flickering and realized where the problem was):
also, I fixed my problem with this mod:
reinforced-mmu2s-extruder-idler
RE: MK3S MMU 2.0S does not load filament the second time
Take your extruder idler door off and peek into the hole where the idle gear shaft sits. You problem sounds just like mine and was caused by the shaft sinking into it's seat and causing the sensor to be flaky. It would trigger but then flicker on and off while printing. I strongly suggest the following mod as it was very helpful in cluing me into what was happening for me (saw it flickering and realized where the problem was):
also, I fixed my problem with this mod:
reinforced-mmu2s-extruder-idler
I will give it a try. This will be my 3rd idler door that I have tried. I don't know what happened. I had several successful prints and then a really bad jam. I had to replace the heat block because the threads pulled out but I replaced it with an E3D block from Matterhackers.
RE: MK3S MMU 2.0S does not load filament the second time
I would only do the idler door mod if you confirm the same problem (shaft is not staying centered in it's seat) because it is a bit tedious getting all the brass inserts to size. The sensor indicator is a good idea regardless, though.
RE: MK3S MMU 2.0S does not load filament the second time
Finally fixed it.
I have 2 prints under my belt now. One was 9 hours.
By far the best fix was the MMU Selector upgrade with a magnet. Several designs out there.
The others were a flag upgrade for the Extruder and an upgrade to the extruder body with a view port on the left side.
Also to help with the grinding filament at the MMU I replaced the tubing from the Buffer with 2mm ID Capricorn tubing. You can feel the different in the friction.
Selector MMU
https://www.thingiverse.com/thing:3688458
Flag
https://www.prusaprinters.org/prints/3417#_ga=2.179760108.914614693.1568993008-936818007.1536362167
Extruder Body
https://www.prusaprinters.org/prints/3676#_ga=2.173451115.914614693.1568993008-936818007.1536362167
Capricorn Tubing