Printing - Tektronix Phaser 340 Service Manual

5
Theory of Operation
5-22 Phaser 340 Color Printer

Printing

At this point, the drum starts rotating again at 190 rpms. As the drum reaches
the correct speed, the ink-jets begin to fire to deposit the image on the oiled
portion of the drum. As the jets fire, the printhead slews in the x-axis to
complete the image on the drum. When the ink image is about 80% complete,
the paper-pick cycle begins.
During printing, all the even-numbered jet sets lay down parallel columns of ink
dots interlaced with columns of ink drops, laid down by the odd-numbered jets.
For 300dpi printing, each even-numbered jet lays down 28 columns of ink drops
interlaced with 28 columns of ink drops laid down by a neighboring
odd-numbered jet. A total of 2,432 columns, each 3,142 dots tall, are laid down.
For 600 x 300 printing, each even-numbered jet lays down 56 columns of ink
drops interlaced with 56 columns of ink drops laid down by a neighboring
odd-numbered jet. A total of 4,864 columns, each 3,142 dots tall, are laid down.
The x-axis motor is stepped at half the rate to double the resolution in the x-axis.
In addition, the printhead jets output smaller, 600 dpi dots.
For transparency printing, the image is printed as a 300 dpi image. 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 the image density of the transparency.
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.