The LCD screen or UV light shows no image

Symptom

The printer seems to run but nothing cures: the build plate and the vat stay empty; or areas of the part are always missing in the same place. The screen test shows dark patches, bright dots, flickering or cracks, or nothing lights up.

Likely causes, from most to least likely

1. The LCD screen is damaged: cracks, pixels or areas that do not work.
2. The screen's ribbon cable is loose, badly seated or damaged.
3. The UV light (the LED panel) does not turn on or has failed; if its fan does not spin, heat can damage it and the screen.
4. Dust or dirt on or under the screen blocks the light.
5. It is not the screen: the exposure is too short or the resin is old, separated or contaminated with alcohol.

Checks to tell which one it is

• Without the vat, lay a sheet of paper on the screen and start the screen or exposure test from the menu. Look at the paper, never directly at the UV light.
• If the paper lights up evenly and the image is complete, the screen and the light work.
• If there are gaps, patches or dots in the image, suspect the screen; if nothing lights up, suspect the UV light.
• If the light comes on but no image appears, check the screen cable.
• Look closely at the screen for cracks.

Before you start

Uncured resin irritates skin and eyes: wear nitrile gloves and safety glasses, ventilate the room and do not look at the UV light. Before taking anything apart or cleaning it, switch the printer off and unplug it, unless a step says otherwise. If in any doubt, stop and ask a professional.

Step-by-step fix

1. Run the screen test

   Remove the vat, dim the room lights, lay a sheet of paper on the screen and start the test from the tools menu. Do not look directly at the UV light.

   Check: The paper lights up evenly and the image appears complete, with no gaps or patches.

   If that does not fix it: Depending on what you see, go on with cleaning, the cable or the UV light.

2. Rule out exposure and resin

   If the test is fine, use your resin's exposure profile, stir the resin if it has separated and replace it if it is old or contaminated with alcohol.

   Check: A manufacturer's test part prints complete.

   If that does not fix it: If it still does not cure, check the UV light.

3. Clean the screen

   With the printer off, remove dust and marks from the screen with a soft, non-scratching cloth, as your manufacturer indicates. Formlabs links small dark spots near the edges to dust, which can be under the screen.

   Check: The test no longer shows those spots.

   If that does not fix it: If they remain, check the cable and the screen.

4. Check the screen cable

   Turn off and unplug the printer. Following the guide for your model, open the base, release the screen's ribbon cable at both ends and seat it firmly again. Also check it for damage.

   Check: After refitting it, the screen test shows the complete image.

   If that does not fix it: Check the UV light.

5. Check the UV light and its fan

   If nothing lights up in the test, with the printer unplugged check the UV LED panel connection and reseat it. While printing, check that its fan spins.

   Check: The light comes on in the test and the fan works.

   If that does not fix it: Replace the faulty part.

6. Replace the damaged part

   If the screen has cracks, gaps or areas that do not light up, or the UV light does not turn on after checking the connections, they must be replaced with spare parts for your model. Contact the manufacturer's support with photos of the test and the connections.

   Check: With the new part, the test passes and the resin cures again.

   If that does not fix it: Contact the manufacturer's support.

Prevention

• Keep the film in good condition so no resin reaches the screen.
• Check from time to time that the UV light fan works.
• Keep the printer away from machines that create dust.

Still not fixed?

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Printers it applies to

Any resin (MSLA/SLA) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Print doesn't appear / Resin does not solidify · Prusa Research
• UV intensity too low #10318 (SL1/SL1S) · Prusa Research
• Inspecting the Backlight Unit and LPU (Form 4 and Form 4L generation) · Formlabs
• [Sonic Mini 4K] Checking the LCD · Phrozen