Head Gap Adjusting Mechanism - Oki ML390 Service Manual

Page: 28
Service Guide ML390/391
Chapter 2 Principles of Operation

Head Gap Adjusting Mechanism

The head gap adjusting mechanism adjusts the gap between the platen and printhead by changing the tilt
angle of the carriage frame. This is accomplished by using the adjusting lever.
Moving the adjusting lever rotates the adjusting screw. The adjusting screw is interlocked with the lever
via a gear. Rotating the adjusting screw changes the angle of tilt for the carriage frame. The printhead is
mounted vertically on the carriage frame. Changing the angle of tilt for the carriage frame moves the
printhead closer to, or farther away from, the platen.
The adjusting cam is used to compensate for differences in the printhead gap when measured at the left
and right sides of the platen. Rotating the adjusting cam changes the height of the guide rail. The height of
the guide rail helps determine the distance between the printhead and platen, when measured at the right
end of the platen.
Turning the adjusting cam to the RIGHT will lower the right side of the guide rail. This causes the
printhead gap (on the right side of the platen) to increase.
Turning the adjusting cam to the LEFT will raise the right side of the guide rail. This causes the printhead
gap (on the right side of the platen) to decrease.
The adjusting lever determines the head gap setting.
Setting 1 is for one or two part forms.
Setting 2 is for three or four part forms.
Settings 3, 4, and 5 are for envelopes and extra-thick paper.
When the adjusting lever is set to position 3, 4, or 5, the distance between the printhead and platen
increases. The electrical contact (attached to the carriage cover) touches a contact pad on the spacing
motor circuit board. This reduces printing speed. Slower speeds ensure adequate printing pressure.
Refer to Section 3.3 for further details on the Printhead Gap Adjustment .
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