Tektronix PHASER 380, Service Manual

Page: 129 / 346

Service Manual 5-27
Theory of Operation
5
In reality, because of the fixed width of the printhead and inter-jet spacing, the
outermost jets cannot interlace completely with their adjacent jets for full-width,
A-size page images with only 5mm(0.25”) side ISO margins. In this case, the
drum rotates for seven extra imaging rotations (14 if both end jets are needed)
for the printhead to reposition the end jets so they can fill-in the missing pixel
columns that cannot otherwise be interlaced.
For transparency printing, the image is printed in the same manner. However,
the image is printed twice on the drum, the second image positioned precisely
over the first image before being transferred to the sheet of transparency film;
this increases image density.
For 600 x 300 dpi printing, each jet lays down 56 columns of ink drops spread
over a 224 pixel-wide field. The drum rotates 56 times to receive the pixel
columns. The same interlace method is used, except 14 pixel columns are
printed between the intermediate 2-step, 1-step and 2-step movements. A total
of 4,864 columns, each 3,134 dots tall, are laid down (for a full-image, A-size
print). The x-axis motor steps at half the rate to double the resolution in the
x-axis. Also, the printhead jets output smaller, 600 dpi dots.
During some diagnostic printing, such as the Service Test Print “Weak Jet,” the
printhead slews to the right and lays down 88 parallel bands of ink. Each band
is about 2.3 mm (0.1 inch) wide and is composed of 28 pixel columns of dots
from an individual jet. As the printhead slews to the right, the drum rotates 28
times; the number of pixel columns each set of jets deposits on the drum. (A set
of jets is one of the 88 vertical arrangements of cyan, magenta, yellow and black
jets.) With no interlacing, the test print reveals the deficiencies of a single jet
compared to the rest.