On Form 4 and Form 4L generation printers, light from the Backlight Unit passes through the Light Processing Unit and resin tank film before curing liquid resin in the resin tank. If the resin does not cure as intended, the cause is usually related to one of those components. In rare cases, an issue with the Light Processing Unit can cause strings or bridges to form between parts on the build platform.

• Thin strings of cured resin spanning gaps between parts or features of parts on the build platform, reminiscent of FDM stringing

• Faulty or damaged Light Processing Unit (LPU)

1. Ensure that the resin tank film is free of debris and damage. If the resin tank is damaged, retry the print with another tank.
2. Clean the LPU release texture.
• Cleaning the release texture (Form 4 generation)
• Cleaning the release texture (Form 4L generation)
3. Replace the LPU. Form 4 and Form 4L generation LPUs are available for purchase on the Formlabs Store.
• Form 4 generation
• Light Processing Unit
• Replacing the Form 4 Light Processing Unit
• Form 4L generation
• Light Processing Unit
• Replacing the Form 4L Light Processing Unit

If the troubleshooting steps above do not resolve the print failure, contact Formlabs Support or your authorized reseller.

To help us provide the fastest and most effective response to your issue, please include the following information:

• Diagnostic logs
• Serial name of the printer
  • The serial name is on the back panel of the printer in the format AdjectiveAnimal or Device-AdjectiveAnimal, where “Device” is the type of device (i.e. Form Wash)
  • You can also tap the printer icon on the Home screen to find the serial name.
• Troubleshooting steps attempted
  • Example: “I reoriented the model in PreForm. I inspected the resin tank and did not notice any damage, clouding, or debris.”
• Resin formulation and lot number
  • The lot number is inside the skirt of the resin cartridge.
• Layer thickness
  • Tap Queue on the Home screen. The Queue screen appears.
• Relevant FORM files
  • If available, attach FORM files of the model to the support request.
• Previous attempts to print the part and any successful prints
• Example: “I printed the file part2.form three times previously. The first and second were successful. The third one failed.”