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How to replace a heatbed thermistor (MINI/MINI+)

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How to replace a heatbed thermistor (MINI/MINI+)

How to replace a heatbed thermistor (MINI/MINI+)
Relevant for:
Last updated 2 years ago
How to replace a heatbed thermistor (MINI/MINI+)
 Difficulty
Very easy
 Steps
20
 Available languages
CSDEESFRITJAPL

Step 1 Introduction

Introduction
Introduction
Introduction
This guide will take you through the replacement of the heatbed thermistor on the Original Prusa MINI and MINI+.
Some parts might slightly differ. However, it does not affect the procedure.
If the heatbed thermistor is damaged, you will see the MINTEMP error message on the display when you preheat the printer.
Heatbed thermistor replacement set is available in our eshop shop.prusa3d.com
Note that you have to be logged in to have access to the spare parts section.

Step 3 Opening the box with the electronics

Opening the box with the electronics
Opening the box with the electronics
Opening the box with the electronics
Turn the printer off and unplug it from the socket!
Release and remove the M3 screw on the box with the electronics.
Remove the printed cable cover.
Lift the second electronics cover slightly. Before you remove it completely, pull it first towards the aluminium extrusion to release both pins from the holes.

Step 5 Removing the heatbed

Removing the heatbed
Removing the heatbed
Removing the heatbed
Remove the steel sheet.
Release and remove 9 screws on the heatbed by using a Torx TX10 key.
Remove the heatbed from the printer.

Step 6 Disassembly the heatbed

Disassembly the heatbed
Disassembly the heatbed
Disassembly the heatbed
Put the heatbed on the clean surface, far from metal parts (screws, Allen keys, ...). There are magnets on the bottom side of the heatbed.
Release and remove the M3x12 screw from the MINI-heatbed-cable-cover-top.
Remove the MINI-heatbed-cable-cover-top.
Remove the MINI-heatbed-cable-cover-bottom.
Remove the textile sleeve all the way from the heatbed cable bundle.

Step 7 Removing the thermistor

Removing the thermistor
Removing the thermistor
Removing the thermistor
Removing the thermistor
Turn the heatbed upside down.
Remove the (yellow) Kapton tape.
Remove the (silver) aluminium tape.
Remove the thermistor from the heatbed and cable bundle.
Keep the thermistor, for now, we will need to shape the new one according to the old one.

Step 10 New thermistor installation

New thermistor installation
New thermistor installation
New thermistor installation
New thermistor installation
IMPORTANT: we need to adjust the shape of the new thermistor to match the old one.
The new thermistor has a pair of straight wires.
The old thermistor is shaped in an "oval".
Guide the thermistor cable through the gap between heatbed cables.
Lay the new and properly shaped thermistor on the heatbed and fix it temporarily using pliers or any other tool.
Make sure the tip of the thermistor is in the circle. If you miss this spot, the printer will read incorrect temperature values.

Step 11 Fixing the thermistor in place

Fixing the thermistor in place
Fixing the thermistor in place
Fixing the thermistor in place
Fixing the thermistor in place
Take the silver aluminium tape and carefully peel off the protective film.
Glue the tape to the heatbed, BUT ONLY in the center of the thermistor (inside the oval shape). We need to double-check the correct position.
Peel or bend the tape slightly, to reveal the tip of the thermistor.
Ensure again, that the tip is right above the circle. If you miss this spot, the printer will read incorrect values.
As soon as the correct position is ensured glue the entire tape to the board.

Step 12 Fixing the thermistor in place

Fixing the thermistor in place
Fixing the thermistor in place
Fixing the thermistor in place
Fixing the thermistor in place
Now it is time to apply the final "yellow" Kapton tape. DON'T PEEL OFF the entire tape, it will curl up!!!
Be careful not to stick the tape over the screw holes.
The Kapton tape has a bigger area than the silver tape. Make sure the silver tape is overlapped from all sides.
Peel off about 0.5 cm (0.2 inch) strip of the Kapton tape and glue it to the heatbed, like in the picture. Ensure the tape is properly connected.
Continue with gluing the tape and stop for a second above the area with the thermistor. Pay great attention to glue the tape everywhere.
Finish gluing the tape to the heatbed. Double-check the entire surface is properly connected.

Step 14 Reassembling the heatbed

Reassembling the heatbed
Reassembling the heatbed
Reassembling the heatbed
Reassembling the heatbed
Turn the heatbed upside down.
Place the MINI-heatbed-cable-cover-bottom under the connectors like in the picture.
Wrap the textile sleeve on the heatbed cable bundle all the way to connectors on the heatbed.
Make sure the connectors fit properly into the cover.
Take the MINI-heatbed-cable-cover-top and slide it over the screw heads.
Secure it with the M3x12 screw.

Step 15 Heatbed cable guiding

Heatbed cable guiding
Heatbed cable guiding
Make sure the textile sleeve is properly inserted in the covers.
Make sure there is almost no gap between both covers.

Step 16 Mounting the heatbed

Mounting the heatbed
Mounting the heatbed
Mounting the heatbed
Mounting the heatbed
Move the Y-carriage all the way to you.
Place the heatbed on the Y-carriage.
Align all 9 holes on the heatbed with the heatbed spacers.
Insert nine M3x4b screws to the holes. DON'T fully tighten the screws.
After all screws are in place, tighten them in the following order:
Center screw
First four screws (edges)
Last four screws (corners)

Step 17 Connecting the heatbed cables

Connecting the heatbed cables
Connecting the heatbed cables
Connecting the heatbed cables
Connect the heatbed thermistor cable in the lower connector on the Buddy board.
Connect the heatbed cable in the lower green connector on the Buddy board.

Step 18 Covering the electronics

Covering the electronics
Covering the electronics
Covering the electronics
Covering the electronics
Before covering the electronics, make sure the square nut is correctly positioned in the printed part. The nut must not fall out! This can cause fatal damage to the electronics.
Insert the cover back in, make sure it is properly seated in the slot. Note: on an older design, there were holes instead of slots, the assembly procedure is the same.
Place the second cover on the top and arrange the cables:
Extruder bundle, ensure the textile sleeve is partially in. Also, it must be tilted away from the printer.
Heatbed bundle, ensure the textile sleeve is partially inside the box.
Filament sensor cable (optional), ensure that the textile sleeve wrapped around the cables is partially inside the box.
Now, tighten the second cover. Check that no cable is pinched.

Step 19 Final check

Final check
Final check
Final check
Final check
Connect the printer and turn it ON.
Use the knob and navigate to the Preheat in the Menu.
Select PLA.
Navigate back to the Info screen and check if the temperature rises.
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