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Replacing the Form 4L resin temperature sensor

The resin temperature sensor measures the temperature of the resin in the tank. The resin temperature sensor is mounted under the LPU with a pair of screws and a pair of spacers. A malfunctioning resin temperature sensor may prevent the printer from printing properly.

Use this guide to replace the Form 4L cartridge floor.

Required Supplies:

Formlabs:

Resin temperature sensor
2 mm hex driver (included in the Form 4L tool cap assembly)
3 mm hex driver (included in the Form 4L tool cap assembly)

Third-party:

Needle-nose pliers or tweezers
Nitrile gloves

Estimated time: 30 minutes

Preparing the workspace

Overview: Prepare the Form 4L and a dust-free workspace for replacing the resin temperature sensor.

Step 1: Remove the build platform

Remove the build platform first to avoid dripping resin onto the Light Processing Unit (LPU).

Step 2: Remove the resin cartridges

Remove the resin cartridges and close the vent caps to prevent resin from dripping off of the bite valve and into the printer.

Step 3: Remove and store the resin tank and mixer

Unlatch the mixer and resin tank. Remove the resin tank and cover it with its lid. Set the tank aside on a clean, flat surface.

Notice:

Wear gloves and hold the resin tank by the tank grips on either side to avoid contamination or damage to the underside of the tank.

Step 4: Prepare the workspace

Clear a workspace around your printer. Ensure that the workspace is well-ventilated and free of dust.

Step 5: Clean the printer

Warning:

Resin may cause skin irritation or an allergic skin reaction. Wear gloves when handling liquid resin or resin-coated surfaces. Wash skin with plenty of soap and water.

Open the printer door and clean any resin pooled around the LPU with paper towels. Dampen the paper towels with isopropyl alcohol if necessary to fully remove the resin.

Danger:

IPA is flammable and presents a fire hazard. Keep containers closed, and keep out of the reach of children.

Step 6: Unplug the printer

Disconnect the power cable from the printer before continuing with maintenance. Do not perform maintenance on the printer while it is connected to power. Wait five minutes after disconnecting the printer from power before proceeding.

Removing the LPU

Overview: Loosen the housing screws and remove the LPU.

Warning:

This step involves removing the LPU, which exposes the Form 4L optical system. When the LPU is removed from the printer ensure that no dust or debris fall into the optical cavity.

Step 1: Loosen the LPU housing screws

Open the printer cover. Use a 3 mm hex driver to loosen the eight captive hex screws in the LPU housing.

Step 2: Unplug the HDMI cable

Carefully lift the LPU and tilt it so that the bottom faces you. Locate the LPU’s HDMI cable. Squeeze the plastic retaining clip and unplug the HDMI cable from the LPU.

Step 3: Disconnect the tank heater cables

On both sides of the printer, the heater cables are oriented with the clip facing outwards. Release the tank heater cables by squeezing the tab on the connectors and pulling directly away from the LPU. Do not pull on the cable itself.

Step 4: Remove the LPU

Remove the LPU from the printer and set it aside.

Removing the resin temperature sensor

Overview: After removing the LPU, remove the resin temperature sensor.

Step 1: Remove the mounting screws

The resin temperature sensor is mounted to the printer with two screws and two spacers. Use pliers or tweezers to hold the spacers while removing the screws. Use a 2 mm hex driver to remove the screws. Set the screws and spacers aside.

Note:

When removing the screws, hold the spacers so they don’t fall into the printer cavity. If a spacer or screw falls into the optical cavity, retrieve it with tweezers. If a spacer or screws falls into the hole under the resin temperature sensor, remove the right panel and use tweezers to remove the screw from the front cavity.

Step 2: Disconnect the cable

Release the resin temperature sensor cable by pressing the plastic tab on the connector. Unplug the cable from the resin temperature sensor. Do not pull on the wires.

Installing the replacement resin temperature sensor

Overview: After removing the old resin temperature sensor, install the replacement resin temperature sensor.

Step 1: Connect the cable

Plug the cable into the connector on the resin temperature sensor. The plastic tab should click into place to secure the connection.

Step 2: Mount and secure the resin temperature sensor

Thread one mounting screw through each of the screw holes in the replacement resin temperature sensor. Slide a spacer onto each of the screws. Carefully lower the resin temperature sensor into place, lining up the mounting screws with the screw holes in the printer frame. Use a 2 mm hex driver to tighten the screws until snug.

Note:

When installing the screws, hold the spacers so they don’t fall into the printer cavity. If a spacer or screw falls into the optical cavity, retrieve it with tweezers. If a spacer or screws falls into the hole under the resin temperature sensor, remove the right panel and use tweezers to remove the screw from the front cavity.

Reinstalling the LPU

Overview: After replacing the resin temperature sensor, reconnect and reinstall the LPU.

Step 1: Connect the tank heater cables

Position the LPU so the cable connectors are oriented towards the front of the printer. Plug the left and right tank heater cables into the connectors on the LPU. The plastic tab should click into place to secure the cable.

Step 2: Connect the HDMI cable

Plug the HDMI cable into the port on the LPU. Ensure that the two prongs on the plastic retaining clip snap into place.

Step 3: Mount the LPU

Ensure that the optical cavity and LPU are free from dust and debris. Place the LPU onto the optical cavity and align the screw holes.

Step 4: Thread the housing screws

Use a 3 mm hex driver to loosely thread the eight captive hex screws in the LPU housing.

Step 5: Secure the LPU

Once all screws are loosely threaded, tighten the screws in a diagonal pattern as shown above. The screws should be secure but not overtightened. To avoid overtightening, grip the short end of the hex driver.

Finalizing the repair

Overview: After installing the replacement resin temperature sensor, power on the printer and perform final checks.

Step 1: Power on the printer

Close the printer cover and connect the power cable to the printer and the power supply. Turn on the switch at the back of the printer. The printer will turn on and initialize.

Step 2: Align the build platform

On the touchscreen, tap Settings > Tools > Align build platform. Follow the on-screen instructions.

Step 3: Run a test print

Insert any missing consumables and upload and start a print. Check that the print starts normally and the parts print successfully. Contact Formlabs Support or your authorized reseller to share the results of the procedure.