The Light Processing Unit (LPU) contains the printer’s laser diode, galvanometer, and other mirrors and lenses that aim the laser along its path for each layer of a print. The Form 3L has two LPUs that sit within the LPU housing, which travels left and right underneath the resin tank. A malfunctioning LPU will prevent the printer from printing properly. The two LPUs can be replaced independently from one another.

Use this guide to replace a Form 3L Light Processing Unit.

Estimated time: 30–60 minutes to replace LPU (2–3 hours with Laser Alignment Print)

Overview: Prepare the Form 3L 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 LPU or into the printer cavity.

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

Remove the resin tank, place it in the resin tank carrier, and cover it with its lid. Set the carrier and 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 cavity

Open the printer cover. Clean any resin pooled on the printer floor, inside the printer cavity, with paper towels. Dampen the paper towels with isopropyl alcohol if necessary to fully remove the resin.

Step 7: Unplug the printer

When prompted by the touchscreen, disconnect the power cable before continuing with maintenance. Do not perform maintenance on the printer while it is connected to power. Replacing the LPU while the printer is connected to power will permanently damage the printer.

Step 8: Clean the LPU housing

Clean any resin in the area of the LPU housing or on the printer with paper towels. Dampen the paper towels with isopropyl alcohol if necessary to fully remove the resin.

Overview: After moving the LPU housing into its maintenance position, remove and unplug the LPU.

Step 1: Cover the laser window

The glass optical window, located on top of the LPU housing, is the opening through which the lasers pass. Cover the window with a lint-free cover, such as several PEC*PADs, to protect it during maintenance.

Step 2: Disconnect the ribbon cable

Both LPUs have a ribbon cable connected to it. The front LPU, accessible from the left side of the LPU housing, has its ribbon cable connected to the end of the LPU oriented toward the front of the printer. The rear LPU, accessible from the right side of the LPU housing, has its ribbon cable connected to the end of the LPU oriented toward the rear of the printer. Locate the ribbon cable for the LPU you are replacing.

There is a small tab at the base of the ribbon cable plug. Press it inward, toward the cable/LPU, and gently pull on the plug to disconnect the ribbon cable from the LPU. You may find it easier to use a small plastic tool, such as a pair of tweezers, to press on the tab.

Step 3: Disconnect the cable harnesses

Aside from the ribbon cable, the front LPU has one cable harness connected to the end of the LPU oriented toward the back of the printer. The rear LPU has two cable harnesses connected to the end of the LPU oriented toward the front of the printer. Locate the remaining cable(s) for the LPU you are replacing.

Disconnect each cable by gripping its plug and gently pulling it away from the LPU.

Step 4: Loosen the LPU screws

Locate the three LPU mounting screws, marked in blue on the LPU’s plastic cover. Use the provided LPU tool to fully loosen the three screws.

The screws are captive and will remain attached to the LPU when fully loose. If any of the captive screws come out of the LPU, thread them back into the LPU before continuing.

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

Step 1: Clean the LPU housing

If there was resin on the old LPU, clean the inside of the LPU housing with paper towels before continuing. Dampen the paper towels with isopropyl alcohol if necessary to fully remove the resin.

Step 2: Prepare the LPU

Carefully remove the new LPU from its packaging. If there is any tape or other packaging covering the LPU mounting screws, remove the tape before continuing. Insert the LPU into the printer in the same orientation as the old module.

Step 3: Insert the LPU into the LPU housing

Grip the replacement LPU and bring it toward the LPU housing, with the blue mark on the top of the LPU cover aligned with the corresponding mark on the LPU housing.

Angle the top edge of the LPU toward the LPU housing, then seat the top edge of the LPU against the top edge of the LPU housing. Swing the bottom edge of the LPU down so the LPU is upright and press the LPU into the LPU housing. When properly installed, the LPU sits stably in the LPU housing.

Step 4: Secure the LPU

Tighten the three LPU mounting screws using the provided LPU tool.

Step 5: Reconnect the cables

Reconnect the ribbon cable to the cable connector on the LPU, ensuring that the cable is fully seated. Reconnect the remaining cable harness(es) to the LPU, ensuring that each is fully seated.

Overview: After installing the new LPU, power on the printer, calibrate the LPU, 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. The printer will initialize, move the LPU housing back to their home position, and perform a calibration.

Step 2: 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.

Step 2: Calibrate the Form 3L lasers (optional)

The Form 3L lasers may require calibration to minimize visible seamlines. If you notice prominent seamlines on your parts, calibrate the lasers by following the instructions in the guide Aligning the Form 3L lasers.