1. Please prepare tools for this chapter:
    • Please prepare tools for this chapter:

      • 2.5mm Allen key for M3 screws

      • 2mm Allen key for nut alignment

      • Needle-nose pliers for zip tie trimming

      • Philips screw-driver for power cable assembly

      • 8mm wrench to tighten the QSM fittings

  2. For the following steps, please prepare:
    • For the following steps, please prepare:

    • mmu2-ele-cover (1x)

    • M3x6 screw (3x)

    • M3n nut (3x)

    • MMU2 control board (1x)

    • Insert three M3n nuts in the ele-cover. Use a flat surface to push them in if necessary.

    • Slide in the MMU2 control board. Make sure the three buttons are all the way through on the other side.

    • Secure the board with three M3x6 screws. Tighten carefully.

    • Tip: If you can't press the nuts in, use a M3x6 screw to pull the nuts in before you slide in the board.

    • For the following steps, please prepare:

    • Power cable for the MK3 (1x)

    • Power cable for the MK2.5 (1x)

    • Use the power cable depending on the type of your printer. In case the cable is missing in your kit, please contact our support.

    • Signal cable (1x)

    • Note the signal cable has two different connectors! One is smooth without safety latch and the other one has a latch. Use the latch for the MMU2 board.

    • Prepare the MMU2 unit and the board assembly as in the picture. Follow the cables to connect them correctly.

    • Signal cable (use side with safety latch)

    • Power cable

    • F.I.N.D.A. sensor cable

    • Pulley motor cable

    • Selector motor cable

    • Extruder motor cable

    • For the following steps, please prepare:

    • Textile sleeve (1x)

    • Zip tie (4x)

    • M3x18 screw (2x)

    • Prepare the MMU2 unit and the electronics assembly like in the picture. Position the side with two motors to the left and signal cable to the left as well.

    • Place the electronics on the MMU2 unit. The connectors must be facing towards you.

    • Secure the electronics assembly with two M3x18 screws.

    • Make sure the selector with F.I.N.D.A. is all the way to the side as in the picture!

    • We will start the cable management from the F.I.N.D.A. sensor and counter-clockwise. Note the arrows.

    • Tighten the cables firmly, but gently at the same time. You can damage (break) the wires.

    • Carefully guide the cable from the F.I.N.D.A. sensor and couple it with the cable from the Selector motor. Use the first zip tie.

    • Continue with the cable bundle and add the Pulley motor cable. Tighten these three cables using a second zip tie near the edge of the printed part (idler-body).

    • Take the signal and power cable (first two from the left). Bundle them together and wrap around 10 cm (3.94 inch) in the textile sleeve.

    • Slide the sleeve towards the MMU2 unit as much as the cable allows.

    • Take the bundle from the motors and F.I.N.D.A. add the textile sleeve above it and tighten it using the third zip tie.

    • Finish wrapping the cables in the textile sleeve.

    • Now using the left hand take the cable from the Extruder motor and pull it gently to the left.

    • Using the right hand take the cable from F.I.N.D.A. sensor (black) and pull it gently to the right.

    • Use the fourth zip tie and bundle all the cables together.

    • Final cable management should be similar to the last picture.

    • Note: for the MK2.5 there will be different connectors at the end of the cable bundle.

    • For the following steps, please prepare:

    • mmu2-rear-PTFE-holder (1x)

    • M3x18 screw (4x)

    • M3n nut (4x)

    • PTFE tube 4x2x650 (5x)

    • PTFE tubes are installed as the last item to avoid damage to them. Be careful during the assembly ;)

    • Carefully turn the entire MMU2 unit upside-down.

    • Slide in the M3n nuts. Use a M3x18 screw to press them in. Use your hand, hammer shouldn't be necessary.

    • The hole for each nut is slightly narrower on the other end, therefore the nut should have a snug fit.

    • Take the first PTFE tube and slide it inside the MMU2 unit. All five tubes are bent in one direction, make sure the free end is now pointing up.

    • There is a circular hole for each PTFE tube, you should be able to press at least 0.5 to 1 mm (0.02 - 0.04 inch) of the tube inside the hole.

    • Continue by pressing in remaining four PTFE tubes.

    • Place the rear-PTFE-holder on the top of the PTFE tubes. Notice the printed part has thicker side, which must be facing out.

    • Secure the rear-PTFE holder using four M3x18 screws. Tighten the screws fully only after you ensure proper alignment of the printed part! Otherwise, you risk squishing the tubes and future filament jams.

    • For the following steps, please prepare:

    • mmu2-frame-holder (2x)

    • M3x12 screw (4x)

    • Be extra careful with the holders from now on. If you break them, you won't be able to mount the MMU2 unit on the frame.

    • While the MMU2 unit is turned upside down, be EXTRA careful with the F.I.N.D.A. cable, which can get broken, if you tilt the unit on the F.I.N.D.A. sensor.

    • Turn the MMU2 unit upside down like in the first picture. Locate the four holes for the M3 screws. Make sure there are nuts in them.

    • Place both frame-holder parts on the MMU2 unit. The longest inclined part should be in the direction of the PTFE tubes.

    • Ensure once again the correct orientation of the frame holders.

    • Secure the holders using four M3x12 screws.

    • Great job, the MMU2 unit is finished!

    • Compare the picture to your assembly.

    • DO NOT ASSEMBLE the MMU2 unit on the FRAME!!! Wait for the instructions.

    • UPDATE: To make the assembly easier, we started shipping hotends with the MMU2 PTFE already installed. Look for a green dot (see the first picture), then there is no need to change the tube. You can skip all the way to the Step 29.

    • Before we mount the MMU2 unit on the printer's frame we have to first change the PTFE tube inside the extruder for a new one, designed specifically for the MMU2. Don't use any other, than the one provided in this kit.

    • In case you have upgraded the extruder's printed parts B6 to B7 and changed the PTFE tube according to the 0.5 Upgrading extruder B6 to B7 included in this MMU2 guide, you can skip to Step 31. If your extruder was already at B7/R3 design before starting the entire MMU2 assembly, please follow these steps.

    • Ensure the filament is not loaded in the hotend. Remove it before proceeding further.

    • For the following steps, please prepare:

    • PTFE tube 4x1.85x50 (1x)

    • Zip tie (2x)

    • The second tube in the package is a spare one.

    • Release marked M3 screws.

    • Remove the fan-nozzle completely.

    • Carefully insert the Front print fan in the X-axis belt.

    • Release and remove all four M3x18 screws on the Left hotend fan.

    • Move the fan carefully away from the extruder body as far as the cable allows.

    • Release and remove both M3x25 screws, then remove carefully the extruder-cover part.

    • Your extruder and fan arrangement should look like in the last picture.

    • Turn the printer around and cut two zip ties on the heater cables. Be very careful while cutting!

    • WARNING: Removing hotend from the extruder needs a "special" technique, then the hotend slides out quite easily. Don't use excessive force, or you will damage some parts irreversibly!!!

    • The hotend is removed by inclining and pulling at the same time. See the first picture showing the WRONG inclination. This hotend is inclined too much to the front and there is no gap between the hotend and the extruder body. Hotend is partly inside and you won't be able to remove it.

    • The second picture is showing the CORRECT inclination. The hotend is tilted, but there is a gap between the hotend and the extruder body. You will be able to remove it.

    • Now, let's incline the hotend properly. Take pliers in the second hand, grab the hotend above heatsink's ribs, pull downwards and slightly towards you. The hotend should "jump" out. Make sure you don't stretch the cables too much or you might damage them.

    • Press the black plastic collet.

    • Remove the PTFE tube from the hotend.

    • Throw this old tube immediately to the nearest trash bin to avoid installing it back by accident ;)

    • Now it is time to insert the new PTFE tube. Note there are two different ends.

    • One end of the tube has "rounded" outer edge. This end must be inside the hotend.

    • Look at the other end, where the tube is drilled inside, shape of the edge is "conical". This is the side, where filament enters the tube. This part must be outside the hotend.

    • Push the black collet in. Slide the tube all the way in and hold it!

    • Using second hand pull the collet out and only then release the tube!!! THIS IS CRUCIAL for the hotend to work properly.

    • Carefully slide the hotend back to the extruder-body.

    • CHECK THE PROPER ALIGNMENT of the hotend in the extruder body. THIS IS CRUCIAL. Otherwise you won't be able to calibrate the printer later!

    • Where to check the alignment:

      • There should be no gap between the extruder-body and the hotend.

      • Last rib on the hotend's heatsink is should be aligned with the printed part. See the photo.

    • Make sure the hotend's cables are on the left side. Compare your assembly with the picture

    • Insert the zip ties in the slots of the cable-holder.

    • ATTENTION! Before tightening the zip ties add the cables from the hotend.

    • Move back to the front side of the printer.

    • Be careful while assembling the extruder! Make sure you don't pinch any wire (e.g. P.I.N.D.A. cable).

    • Assemble back the extruder-cover and tighten both M3x25 screws.

    • Guide the motor cable back in the slot.

    • Move back the Left hotend fan and tighten all four M3x18 screws. Tighten carefully, you can crack the plastic frame of the fan.

    • Place back the Front print fan and the fan-nozzle. Tighten all three screws. Proceed carefully, you can crack the plastic frame of the fan.

    • Extruder is reassembled! Let's continue with the MMU 2.0 assembly.

    • For the this step, please prepare:

    • mmu2-filament-sensor-cover (1x)

    • PTFE tube 4x13 (1x)

    • Use a new PTFE tube (short 13 mm), which is in the MMU2 upgrade kit.

    • The new PTFE tube and mmu2-filament-sensor-cover are in the bag nr. 3.

    • Release both M3x10 screws and remove the old filament sensor cover.

    • Remove the old PTFE tube and replace it with new one. You can insert the tube in the extruder body first or in the filament sensor cover.

    • Install the new filament sensor cover and tighten it with the M3x10 screws from the previous cover.

    • For the following step, please prepare:

    • PTFE tube 4x2x360 (1x)

    • Fitting QSM-M5 (2x)

    • Note this tube, can be also white. The dimensions and properties are the same.

    • Take one QSM-M5 fitting and slide the PTFE tube inside. You should feel the tube snapped in.

    • Repeat this procedure on the other end.

    • As an alternative, you can first screw the fittings in the printer and then slide the tube in.

    • For the following steps, please prepare:

    • Original Prusa i3 MK3 printer

    • MMU2 unit

    • PTFE tube

    • 8mm wrench

    • The MMU2 unit should be placed in the middle on the top part of the aluminium frame (next to the Prusa logo).

    • Place the unit on the frame, do not try to fix it for now.

    • Look from behind the printer, there are "clamps" on the MMU2 unit, which must be snapped (locked) to the frame. Don't do it now, wait for the next step!

    • Make sure once more the unit is in the middle of the frame, once we engage the clamps, you won't be able to move it!

    • Using both hands, apply equal pressure along the top part of the MMU2 unit. Press downwards and slightly towards the frame. Press until the clamps lock to the frame.

    • Check on the front side of the frame, both clamps of the holder are fully engaged.

    • That's it for the MMU2 unit ;)

    • Take the PTFE tube you prepared earlier and connect it to the extruder. Both ends of the tube are the same. Use fingers to tighten the thread.

    • Take the second end of the tube and connect it to the MMU unit. Tighten the fitting using fingers.

    • Check both fittings on the tube are perpendicular to the surface of the extruder and the MMU unit. Make sure the tube is not distorted or twisted.

    • Tighten both fittings using the 8mm side of the wrench, be very careful when tightening, don't use an excessive force!

    • Using 2.5 Allen key release the M3x40 screw and open the RAMBo-door.

    • Open the door, release the M3x10 screw and remove the upper hinge.

    • Remove the door.

    • Note your heated cable wrap can be textile or a spiral wrap. It doesn't affect this build.

    • Connecting MMU2 unit to the printer differs depending on the printer you have. For the MK3, please use this step. For the MK2.5 please skip to the next.

    • Signal cable (upper row of the pins, brown wire in the connector facing left)

    • Make sure the signal cable is connected to all pins! You can use the filament sensor connector to verify the alignment.

    • Power cable (add it to the first two clamps from the left, leave the PSU cables connected). Red wire is positive and in the first slot, black wire is negative and in the second.

    • The power cable connector "fork" has bended ends, make sure they point up, see the picture.

    • Make sure the power cables are tightened firmly!

    • Use the Philips screw-driver to release the screws on the EINSY.

    • This step is for the MK2.5 owners, in case you have MK3, please skip to the next.

    • Signal cable (upper row of the pins, brown wire in the connector facing left)

    • Make sure the signal cable is connected to all pins! You can use the filament sensor connector to verify the alignment.

    • Follow the cables from the PSU and unplug one connector from the RAMBo board (both are the same).

    • Connect the PSU cable to the power cable from the MMU2 unit. See the picture and ensure the connector is all the way in.

    • Plug the power cable from the MMU2 unit to the board, where the PSU cable was plugged previously.

    • Make sure the power cables are connected firmly!

    • WARNING: we need to cut part of the plastic. Make sure you wear protective eyewear!

    • Using pliers carefully cut the corner of the door. We need to create a space for the MMU unit cable bundle.

    • Comparison between the trimmed door (left) and the original shape (right).

    • Place the door back.

    • Insert back the hinge.

    • Tighten the M3x10 screw.

    • Insert the cable bundle from the MMU unit.

    • Close the door and make sure no wire is pinched.

    • Tighten the M3x40 screw.

    • Your sweets are well deserved, this was a tough part!

    • Electronics assembly is the last chapter with high level of difficulty, consume 25 %.

    • Congrats, you've made through the toughest part of the build!

    • Check the final look of the printer.

    • Last assembly is in front of us! 4. Spool holder assembly

Finish Line

145 other people completed this guide.

Jakub Dolezal

Member since: 02/20/2017

118,703 Reputation

162 Guides authored


Prusa Research Member of Prusa Research


3 Members

303 Guides authored


For those who have a Mk2.5 and are installing the MMU2.0, beware that the MMU2.0 steppers may be 24v and start to whistle when you turn on the printer. Although the unit will boot and steppers will run it is not advisable to use it yet. Prusa support is working on that and will inform the Mk2.5 users about what to do.

Francisco Bischoff - Reply

Hi Francisco, I also suggest to wait until the instructions are updated with the MK2.5 MMU2.

Jakub Dolezal -

I had this same whistling issue on my mk2.5 too, and with the latest firmware that Prusa posted this weekend (I updated both the MMU2 and my printer’s firmware), it fixed the issue.

Chris Goodwin -

Pictures should show existing wires also. thanks

John Tucker - Reply

Hello! You mean the photos in step 38? The other cables are not there for better clarity, the photo would be showing just a big cable mess otherwise.

Martin L. - Official Prusa CS -

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