In Form 4L generation printers, the printer’s backlight shines through a component called the Light Processing Unit 4L (LPU 4L) to print. The LPU 4L contains an LCD panel, heaters, and sensors that form an important part of the Form 4L optical system. The LPU mounts to the Form 4L and sits under the resin tank. A malfunctioning LPU can prevent the printer from printing properly.

Use this guide to replace the Light Processing Unit 4L (LPU 4L).

Estimated time: 15–30 minutes

Overview: Prepare the printer and a dust-free workspace for replacing the LPU.

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 valves 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.

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

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

Step 6: Unplug the printer

Disconnect the power cable 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.

Overview: Loosen the housing screws and remove the LPU.

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 for disposal with electronic waste.

Overview: After removing the old LPU, connect and install the replacement.

Step 1: Connect the tank heater cables

Position the LPU so the cable connectors are oriented towards the front of the printer. Plug the 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.

Overview: After installing the replacement LPU, 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 initializes.

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.