UV Printer nozzle is normal, but a specific color is missing during printing ARTJET 2026

• When ink enters the Damper from the main ink bottle via the ink tube, it passes through the print head, flows to the captop, moves through the motor pump, and finally drains into the waste ink bottle.
• This article covers When a Specific Color Drops Out During Printing in the full ink supply problem series.
• This follows Part 1 Captop Lower Tube, Part 2 How to Replace the Captop, Part 3 Damper, Part 4 Pump Motor and Yellow Tube, Part 5 Captop and Head Position, Part 6 Aligning the Captop and Head Position, Part 7 When the Capping Station Level Is Not Correct, Part 8 Captop Surface Drying, Part 9 Degraded Ink Inside the Captop, Part 10 Time for Ink to Fill the Damper, Part 11 Ink Tube Burst, Part 12 How to Replace a Motor Pump Tube, Part 13 Why White Cleaning Doesn’t Work Well, Part 14 Why It’s Important to Replace the Yellow Tube and Captop, Part 15 Head Protection Plate Crumpled, and Part 16 Head Protection Plate Cracked.
• In this article, we explain a case that kept recurring even after replacing the Damper, ink tube, Captop, and head — and what the real cause turned out to be.

We’ve seen plenty of White issues before, but this time it’s Lc or Lm not appearing at all during printing.

Everything else works fine.

• Ink load (pumping) is normal
• Print head cleaning is normal
• Nozzle pattern is also nearly normal after cleaning

When the color suddenly shifts mid-print and we stop printing to check,

• printing a nozzle pattern without cleaning shows Lc or Lm mostly missing,
• which looks similar to what you’d see with degraded ink or an ink shortage.
• The symptom doesn’t show up every time — sometimes it prints perfectly fine.
• But with nothing changed, ink drops out at other times,
• and once, we thought it was fixed after 5 clean prints — only to see it drop out again on the 6th.

Damper replacement

• Thinking “maybe the Damper is faulty,” we replaced it —
• problem not resolved.

Replacing the entire ink tube from the main tank to the Damper

• Wondering “could the ink tube have a tiny tear affecting supply?” —
• even though it’s tedious work, we replaced the whole ink tube from the main bottle to the Damper —
• problem not resolved.

Captop replacement

• “Could there be degraded ink left inside the Captop?”
• Since we’d seen something similar on a White ink Captop, we replaced it just in case
• The problem went away after replacing it,
• but the same problem came back two weeks later!

Print head replacement

• By this point, we’d replaced everything related to ink supply, from the ink line to the Damper and Captop.
• Finally, we decided to replace the head — the last gateway the ink passes through.
• Since this wasn’t a DATA-related issue, we didn’t expect replacing the head to matter, but we did it anyway just to rule it out.
• Sure enough, it wasn’t a print head problem.

Since replacing everything hadn’t solved it, we started organizing our thoughts step by step.

One clue stood out: “replacing the Captop keeps the same problem from showing up for a while.”

• We approached it as a Captop-related issue.
• This customer had installed two units together, and one had no issues at all.
• We closely compared the Captop from the working unit to the one on the problem unit.
• On the normal unit’s Color Captop, the felt showed no particular color staining overall (left side in the photo below).
• On the problem unit, the color wasn’t spread evenly — instead, the right side was distinctly stained red.

The red staining on the Captop’s right edge simply means one thing:

• Lm ink is continuously flowing through that spot.
• That continuous flow means the Lm nozzle is touching the felt inside the Captop, constantly drawing ink out of the head,
• and since the ink inside the head comes from the Damper, it means the Damper’s ink is also being continuously drawn out.

In other words, with the Lm nozzle touching the felt while capped,

• all the ink sitting in the Damper gets drawn out,
• leaving the Damper empty.
• Printing runs fine at first on whatever ink is left in the Damper,
• but partway through, the ink supply runs out and Light Magenta stops printing.

Here’s how capping works:

• The motor raises the entire capping unit,
• and the spring under the Captop lets it contact the print head’s underside gently,
• until the capping unit finishes rising and the spring fully compresses, creating a tight seal between the print head and Captop.
• Outside air is blocked at this point because the Captop’s black rim is made of elastic rubber.

As the Captop rubber weakens,

• setting the capping unit height too high seals the print head more tightly, which can help cleaning,
• but over time the Captop’s rubber blade gradually sags.
• Printing worked fine right after replacing the Captop because the fresh rubber blade kept the print head surface off the Captop felt.
• But as the rubber compressed and weakened over time, the print head nozzle started touching the Captop felt,
• and that’s when ink inside the Damper began leaking into the felt, causing the problem.