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Service Guide ML390/391
Chapter 3 Maintenance & Disassembly
3.3.01 Printhead Gap Adjustment
Before performing this adjustment, always verify that the printhead is properly installed.
The printhead gap should measure:
0.016 inch, + / - 0.002 inch (0.41 mm, + / - 0.05 mm)
The printhead gap adjustment procedure should be performed when the following occur.
· Print quality is darker on either side of the document.
· Parts /Assemblies are replaced.
Space Motor Assembly (3.2.15)
Carriage Shaft (3.2.16)
Guide Rail (3.2.18)
This adjustment has four phases.
· Setup Phase (Steps 1-6)
The cover is removed and the printhead is placed at a known reference point.
· Printhead Gap Modification Phase (Steps 7-9)
The distance between the printhead and the platen at the left (line feed motor) side of the platen is
modified by turning the adjust screw. Turning the adjust screw varies the vertical position of the space
motor.
· Parallel Adjustment Phase (Steps 10 - 12)
The adjust cam lever is moved to ensure that the printhead moves parallel to the platen.
· Verification Phase (Steps 13 - 14)
This phase verifies that the Parallel Adjustment Phase did not affect the Printhead Gap Modification
Phase.
To adjust the printhead gap, follow this procedure.
1. Remove the upper cover.
2. Move the change lever to the rear paper feed position.
3. Place the paper bail bar in the OPEN position.
4. Set the adjusting lever to Position 1.
5. Place the adjust cam in the vertical position.
6. Slide the carriage assembly to the left (line feed motor) side of the platen.
7. Use a feeler gauge to check the printhead gap. The printhead gap must measure:
0.016 inch, + / - 0.002 inch (0.41 mm, + / - 0.05 mm)
8. Use a straightened paper clip to press down on the adjusting gear. This separates the gear from the
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