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Frozen screen, garbled symbols or restarts in the middle of a print

Guide based on the manufacturers' official documentation; usi3d has not yet verified it on a machine.

Technology: FDM · Symptoms: Frozen screen or restarts · Updated on 9 October 2026

Symptom

The screen freezes or goes blank, shows strange symbols, or the printer restarts or stops mid print. On Klipper setups, the computer running it (for example a Raspberry Pi) reboots or the connection to the board is lost.

Likely causes, from most to least likely

  1. Insufficient or unstable power: a borderline supply whose voltage drops with the bed and hotend heating and fast moves, or a poor supply for the Raspberry Pi.
  2. Loose or damaged cables: the display ribbon cable or the board connectors.
  3. Firmware for another model or corrupted firmware: the display shows garbled characters.
  4. A problematic file or storage device when selecting or sending the file.
  5. An electrostatic discharge when inserting the SD card, which leaves the display glitching until a restart.

Checks to tell which one it is

  • Does it happen mostly with the bed and hotend heating and fast printing? That points to the power supply, especially if it stops happening when printing slower or with the bed off.
  • Did the strange symbols appear right after a firmware update? Firmware for another model was probably installed.
  • Does it hang when selecting a file from a drive? Try another drive formatted as FAT32.
  • In Klipper, check whether the Raspberry Pi shows under voltage warnings or whether “Lost communication with MCU” errors appear.
  • If the heaters stay on when it freezes, treat it as an emergency: switch the printer off at the switch.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

  1. Switch it off and on

    Turn the printer off with its switch, wait a few seconds and turn it on. If the bed or hotend kept heating while frozen, switch it off at once: hung firmware may not be controlling the heaters.

    Check: The printer starts and works normally.

    If that does not fix it: Check the file and the storage.

  2. Change the drive or the file

    If the fault appears when selecting or sending a file, try another USB drive or card formatted as FAT32 and copy the file again.

    Check: The file opens without the screen hanging.

    If that does not fix it: Check the power supply.

  3. Check whether it's the power supply

    Try printing slower or with the bed off (with a material that allows it). If it doesn't hang that way, the supply can't cope or is failing: contact support to have it checked or replaced. In Klipper, use a good power supply and cable for the Raspberry Pi and fix any under voltage warning.

    Check: The print finishes without restarts.

    If that does not fix it: Check the cables.

  4. Check cables and connectors, unplugged

    Unplug the printer. Check that the display ribbon cable is fully seated, the right way round and not deformed, and that the board connectors are secure and undamaged. Don't plug or unplug cables with the printer on.

    Check: The display works properly and there are no restarts.

    If that does not fix it: Reinstall the firmware.

  5. Reinstall the correct firmware

    Download the exact firmware for your model from the official website and install it following the manufacturer's guide. If the fault persists, try a factory reset if your printer has one.

    Check: The display shows normal text and doesn't hang.

    If that does not fix it: Contact your manufacturer's support.

Prevention

  • Use a suitable power supply and, with Klipper, a good supply and cable for the computer.
  • Only update with the official firmware for your exact model.
  • Don't plug or unplug cables with the printer switched on.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.

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