In the Form 3/Form 3B, the printer optics - the laser diode, mirrors, and other components - are contained in a module called the Light Processing Unit (LPU). The LPU, sitting inside the LPU housing, moves left and right in the printer during each layer of a print. The laser beam exits the LPU through an anti-reflective coated glass optical window mounted on top of the unit. The window preserves print quality and reliability by protecting the LPU components from dust, oil, and resin contamination. Keep the glass optical window clean to ensure successful prints.

The LPU housing, with the LPU, rollers, and optical window, sits in the LPU garage on the right side of the printer when a print is not running. The garage protects the optical window from most forms of contamination, but dust can still accumulate on its surface over time. As the laser passes through the optical window, any such contamination can cause the laser light to diffuse or weaken, resulting in print defects.

To maintain the glass optical window, inspect the optical window surface for dust, oil, or contamination using a flashlight, LED, or cell phone light. If dust, oil, or contamination is noted, clean the glass surface following Formlabs instructions. As with most optical surfaces, minimal cleaning is the best cleaning.

Estimated time: 10 minutes

Always remove the build platform, resin cartridge and resin tank before performing maintenance on the printer to avoid dripping resin into the printer cavity.

1. Lift the platform lock and remove the build platform.
2. Close the resin cartridge vent cap and remove the resin cartridge.
3. Remove the resin tank from the printer. Place the resin tank in its case.
4. Cover the resin tank case and set it aside with the build platform and resin cartridge on a clean, flat surface.

Inspect the optical window for dust, oil streaks, fingerprints, or cured resin.

1. With the printer plugged in and powered on, tap the wrench icon to access the Settings screen, then tap Maintenance > Motor Moves. The Motor Moves screen appears. Tap and hold Left (<) to move the LPU housing to the middle of the printer cavity. Other controls on this screen fully sweep the LPU housing across the printer cavity and control the build platform carriage.
2. Disconnect the power cable before continuing with maintenance.

3. Shine a secondary light source (for example, a flashlight, LED or cell phone light) onto the optical window to reveal any hidden contamination on the glass surface.
   • Hold the light source at the shallowest angle possible. From the edges of all three accessible sides (that is, left, front, and right), scan the light back and forth across the optical window.

4. If there is any contamination on the underside of the optical window, remove the roller holder to access and clean both sides of the glass optical window. Follow all the steps in the guide Cleaning the Form 3 roller holder [EN] [DE] [ES] [FR] [IT] [JA] [ZH].

Remove dust and other loose contaminants, which can interfere with the laser.

1. Use a rubber bulb air blower to gently remove any visible dust from the optical window.
   • Make sure to remove any large particles that may scratch the glass surface.
   • If a rubber bulb air blower is not available, compressed air may be used.
2. Use a new PEC*PAD to remove any remaining dust from the optical window with a dry wipe.
   • Wipe slowly, pulling the PEC*PAD toward you, repeating until you have cleaned the entire glass surface.

Proceed with a wet wipe only if the dry wipe does not clean the glass completely.

Wet wipe the optical window only if oil, smudges, fingerprints, or resin contamination is visible. Only use IPA to clean the glass surface as any other cleaning solution may degrade the anti-reflective coating.

1. Apply a small amount of IPA to a new PEC*PAD.
2. Wipe the optical window slowly with the PEC*PAD, pulling the PEC*PAD toward you. Repeat this step until you have cleaned the entire glass surface.
3. Use your secondary light source to inspect the optical window. Repeat the wipe if any streaks are visible.
   • Multiple passes may be necessary to achieve a streak-free surface. Each PEC*PAD can be used multiple times by refolding the material to expose a fresh surface for each pass on the glass panel.
4. Dry wipe the glass surface again with a new PEC*PAD to remove any remaining streaks.
5. If any streaks remain, remove the roller holder to access both sides of the glass optical window. Follow all the steps in the guide Cleaning the Form 3 roller holder [EN] [DE] [ES] [FR] [IT] [JA] [ZH].

If streaks are difficult to remove, contact Formlabs Support or your authorized reseller. When requesting help, please provide photos of the optical window illuminated by a secondary light source and a list of attempted cleaning steps.

After cleaning the optical window, power on the printer to complete the maintenance process. Close the printer cover and connect the power cable to the printer and the power supply. The printer will initialize and the LPU will move back to its home position to perform a calibration.