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Replacing the Thermistor

The thermistor is a critical sensor that measures the temperature of your hotend. If you get MINTEMP or MAXTEMP errors, or if the temperature readings are erratic, the thermistor may be damaged and need replacement. This guide explains how to replace it on your MY-Mini 3D Printer.

Tools Required

  • Hex key set
  • Small screwdriver (for the mainboard terminals)
  • Pliers or tweezers
  • Zip ties
  • A new thermistor compatible with your printer's firmware

Safety First

  • Turn off and unplug the printer: Ensure all power is disconnected.
  • Let the hotend cool down: Make sure the hotend is at room temperature before you begin.

Procedure

1. Access the Hotend

  1. Remove the print head cover or shroud to get to the hotend assembly.
  2. The thermistor is the small component with two thin, delicate wires, usually with a glass bead at the end.

2. Disconnect the Old Thermistor

  1. Trace the thermistor wires from the hotend back to the mainboard. You will likely need to open the electronics enclosure.
  2. Disconnect the thermistor connector from the mainboard.
  3. Carefully cut any zip ties and unroute the thermistor wires from the print head back to the mainboard.

3. Remove the Old Thermistor

  1. The thermistor is usually held in the heater block by a small screw. This screw should be just tight enough to hold the thermistor in place without crushing the delicate glass bead.
  2. Carefully loosen and remove this screw.
  3. Gently pull the old thermistor out of the heater block. Be careful not to damage the wires, as you may need to pull them through some tight spaces.

4. Install the New Thermistor

  1. Carefully insert the new thermistor into the hole in the heater block.
  2. Re-insert the retaining screw. Be extremely careful not to overtighten it. The screw should be just snug enough to prevent the thermistor from falling out. Overtightening can crush the glass bead and destroy the new thermistor.
  3. Route the new thermistor wire back to the mainboard, following the same path as the old one.
  4. Plug the new thermistor into the correct port on the mainboard.

5. Reassemble and Test

  1. Tidy up the wiring and use new zip ties to secure it.
  2. Reattach the print head cover and any other parts you removed.
  3. Plug in and turn on the printer.
  4. Check the temperature reading from the hotend on the printer's screen. It should show the current room temperature.
  5. Set the hotend to a low temperature (e.g., 50°C) and verify that the temperature reading rises and stabilizes correctly.

By following these steps, you can carefully replace a faulty thermistor and resolve temperature-related printing issues on your MY-Mini 3D Printer.