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Prusa Mk2 Major Jam up due to broken Hot End Fan wire

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  • Prusa Mk2 Major Jam up due to broken Hot End Fan wire

    OK I went to help Mike do a 3D print tonight and we had problems with filament not extruding... so checked through the steps.

    1. Checked active bowden tube - all good.
    2. Pulled off the "manifold" where the 4 tubes converge to 1 - Aha! There was a piece of yellow filament stuck inside of one of the bowden tubes and going into the hot end. Gave it a tug and its jammed up good.
    3. Started to take apart the top end of the hot end, and after some reading found that jams can happen in the teflon tube on top of the hot end. This can be removed by pressing down on a little black plastic ring and extracting the white tube like in the photos. There was a big mushroom head jam up.
    Click image for larger version

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    But wait there's more, inside the actual hot end was a whole bunch of plastic, which I could only get to by removing the nozzle and hot end and then clearing it out with a small drill bit and removing that little black plastic ring - which is actually a clip. So the jam has been cleared.

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    BUT while working we noticed that the little fan at the hot end kept kicking on and off, and after pulling out the hot end noticed a wire had come dislodged.
    Mike is trying to re-solder that wire in, to which I wish him luck

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    The fan failing seems to be the root cause of the jam up, by letting the filament in the hotend melt there rather than just at the nozzle.
    Last edited by Garret H; 03-04-2019, 09:25 PM.

  • #2
    This might be the fan we need here:


    • #3
      managed get at the solder connections on the fan, and soldered the wire back on, then put it back on...tried preheating...and the fan did not kick in...not sure if it only kicks in when printing or could be the fan needs to be replaced...could be the that the little collet thing that flew away durring disassembly is essential for the fan to run? anyway...would be cool if someone else can look at it, to confirm its state...
      thanks to Garret for getting the nozzle unclogged...


      • #4
        Synchro can you flip the indicator to red then? Put a note on the machine.
        if someone puts filament in without that fan going its going to make a big messy jam all over again.


        • #5
          I think this is what we're looking for. Any objection to rolling the Prusa back to single material?
          Cheap Fans & Cooling, Buy Directly from China Suppliers:2 pieces Gdstime 12 Volt Sleeve Bearing 1 inch Small DC Mini Blower Cooling Fan 30mm x 10mm 12V 3cm 30x30x10mm 3010 3D Printer Enjoy ✓Free Shipping Worldwide! ✓Limited Time Sale ✓Easy Return.


          • Garret H
            Garret H commented
            Editing a comment
            Thats only a 2 bolt flange, its quite different too with side air draw and not direct thru. The fan needs to push air over the hot end, not suck. Not sure the direction of that one?

        • #6
          I ordered two of these fans:

          They will be here March 11, that was the best delivery date I could find.


          • #7
            awesome, was just about to look into ordering, thanks for this Garret


            • #8
              Any objection to rolling the Prusa back to single material?
              Currently the feed motor for channel 1 is apparently malfunctioning and feed line 4's bushing has broken. I think it should be safe to return it to single feed until these two major problems are addressed.


              • #9
                I recieved the new fans, will drop them off in the morning. I have a suspicion that I went and ordered the wrong size in my rush. Whatevs we can mount with zip ties until I get the right one.


                • #10
                  Yep the fans are too large. I should have gotten 30x30x10mm fans. I'll get the correct ones on the way ASAP.

                  in the meanwhile it should be possible to hack these in place by slotting out thet top corner bolt hole a little and notching the housing to clear the part fan duct.

                  I ordered the right one:

                  BUT it won't be here until later March or early April.

                  I can find time to hack the temporary fan, maybe, next week.
                  If anyone takes a swing at it, makes sure nothing protrudes past where the original fan was or else it will collide with the Z-axis screws. Strapping it to the side won't work, it needs to stay within the original 10mm thickness.
                  Last edited by Garret H; 03-08-2019, 11:10 AM.


                  • #11
                    noticed the required fan sitting on the hack table attached to another extruder end...this fan had a connector on it...happened to have the female end...removed the broken fan and spliced the connector in with some solder and shrink tube...plugged the fan in, and tested works...tested printing with a small technicolor triangle, seemed to print i should note that because i failed to put a note on the printer it was used without the fan working, and that print seemed to look ok when i saw it before it was interrupted...anywho, the fan is working now and it seems to be printing...can look into the multi filament stuff at another point, i used/tested tube #2, pretty sure Garret, cleared an end from tube 1...not sure about the other 2...guess the next step is to test em...
                    for another time...
                    for now i think we can say it is back in operation i guess...

                    hope this is cool that i grabbed the fan from the extruder sitting on the table, can easily undo if needed...the fan has a connector on it now...


                    • #12
                      New issue with the printer: it seems filament keeps breaking just ahead of the extruder. This is a new issue since the fan was installed.

                      The cabling and wrap going to the print head seems like it wants to bind up on the filament when it's at just the right angle.

                      I don't remember this zip tie being attached to the frame before? Unless anyone opposes I'm going to clip it off.


                      • #13
                        Stopped by the space for a bit tonight and saw the Mk2 was marked as down. Synchro told me it was a jam up, and him and Hunter got to work disassembling it.
                        The plastic teflon guide tube that goes into the hot end had filament jammed in there real good. Hunter, Mike and I managed to get it clear,but it ended up getting pretty mushroomed in the process. So I took a chunk of spare bowden tubes, cut it to length and glued a keeper ring onto it. The old teflon tube is in the tray if this doesn't work well...

                        That wasn't enough in itself, part of the hot end just upstream of the nozzle was totally plugged up. I took this apart and Hunter gave me a hand with a hot air tool and we got it cleaned down to bare metal.

                        The Mk2 SHOULD be printing now. If it isn't working then the cooling section may have some other garbage in that, I forgot to check it.
                        I am thinking that the little section I clear tonight may have had some residual plastic in it that I didn't clear last time, and that was the source of the problem.... time will tell.

                        EDIT: Ah crap this might not work... I was looking for a schematic of the hot end and found this link:

                        In the photo it shows that the PTFE (Teflon) tube is supposed to be tapered.... which explains why it was jammed up so horrendously bad. This also probably isn't going to work reliably for Multi-material prints.

                        The taper in the photo is an exaggeration. Further research found this article, you can just drill in the taper with a 60 degree angle bit. Problem is the MMU has to be between 1.85 and 1.9 mm inside diameter, the tube I used is likely 2.0 mm inside.
                        How to trim:

                        About the tube:

                        You can buy the regular tube here but its NOT Mk2 MMU compatible:

                        We should just take the Multi-material head off and stick with the reliable single material extruder.
                        Last edited by Garret H; 04-13-2019, 08:38 PM.


                        • #14
                          On a Prusa owners forum I found the following post on how to tune in the MMU:

                          "The three biggest challenges for me have been:

                          Filament resistance - fixed by adding my M10 "festo" connection add-on to the filament buffer and also by adding the improved filament spool rollers to Prusa's filament trays. Also added the M10 festo mount to the back of the MMU2.
                          Bulbous filament tips - fixed by using David's Torlon tube *and* adding a titanium heatbreak that had a snugger-fitting PTFE cup. I think one could get by with just David's torlon tube.
                          Stringing tips - these can get folded back in and jam the extruder. Erik's awesome "skinnydip" script for Slic3r (set at insertion length = 33 for me) has virtually eliminated this.
                          As of last night, I can *finally* run this thing unattended.
                          It's been an uphill battle so far, but totally worth it, and it's only going to get better as people improve it through mods and code improvements. Super thankful to the folks on this forum who have helped me."


                          • #15
                            More spare parts have arrived. I have a new hot end, more thermistors, and some silicone boots which are supposed to do three things:
                            keep the end warm
                            keep the end clean
                            reduce stringing by shielding the print from the heat of the hot end.

                            We can try the boots and see if they are worth having.