Color Pair Missing (Completely, Or Almost Completely); All Channels Missing; Some Nozzles Missing - Epson Stylus pro 7900 Repair Manual

Pro 7900 and 9900 Field Repair Guide
It can be verified by gently injecting water into the suspected inlet. If the channel accepts water,
the Print Head is probably not the issue. Because of the cost of the Print Head, verification is
recommended.
4. Replace the Ink Bay.

Color Pair Missing (completely, or almost completely)

The most likely cause of a missing color pair is poor cleaning by the Cleaning Station. That is because
the only thing in common with a color pair is the Cleaning Station.
1. Replace the Cleaning Station.
All Channels Missing (completely, or almost completely)
This symptom can be caused by Ink Supply issues, Main Board issues, or Cleaning Issues.
1. Execute a "Normal" cleaning, and observe the Waste Ink Tube (Ink Exit Tube) from the Cleaning
Unit.
1.1 If the ink flow in the Waste Ink Tube looks normal, replace the Main Board.
2. Replace the Cleaning Unit.
3. Replace the Ink Bay.
Some Nozzles Missing (but not all) (1 or more channels)
This condition is normal after a period of inactivity. It can also indicate a defective Print Head. It is
complicated by "reverse flow". This procedure describes how to differentiate the issue.
1. Perform a Nozzle Check and mark it as #1.
Missing Nozzle Diagnosis
Printer Component, Software Item, LCD Display, Printer Button
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