CRT
Display Focus
98750
Adjustments 6-1
Chapter 6
Adjustments
The focus should be checked whenever the A7S or the CRT/yoke assembly has been changed.
The focus control
is
located on the A 75 assembly inside the high voltage cage. Remove the
CRT top cover
and
the high voltage cage cover to access the A75 assembly (see Figure 6-1).
Display a
full
raster pattern of characters; the test
ROM
CRT alpha test
will
provide these
patterns. Adjust the focus control to sharpen the appearance of the displayed characters.
It
may
not be possible to focus
all
areas of the display at a particular control setting;
in
this case, the
focus control should be set at the point that gives the best overall display appearance.
CRT Intensity
The intensity should be checked whenever the A75 or the CRT/yoke assembly has been
changed.
The intensity control
is
located on the A 75 assembly inside the high voltage cage. Remove the
CRT top cover
and
the high voltage cage cover to access the A75 assembly (see Figure 6-1).
To adjust the
CRT intensity, use the following procedure.
1.
Advance the A75 intensity control and the operator's intensity control on the lower right
corner of the
CRT bezel to maximum intensity.
2.
With both controls at maximum settings, horizontal retraces should appear on the CRT.
Adjust the A 75 intensity control until the retraces are no longer visible.
3.
Press the CRT test button and notice the intensity of the
full
raster display.
4.
Use the A 75 intensity control to reduce this intensity by approximately
1fz.
This control
setting
is
between
l/s
and
1/4
of a turn less on the A75 intensity control.
5. Adjust the operator's intensity control
for
the desired intensity.
6.
Reassemble the computer.
CRT
Alpha Raster
Size
The alpha raster size should be checked whenever one of the CRT section assemblies has
been
changed. To adjust the alpha raster, use this procedure.
• Remove the CRT top cover.
• Press the CRT test button on the A73 assembly, shown
in
Figure 6-1, to display the alpha
raster
in
inverse video.
• Use the alpha width
and
alpha height controls on the A74 assembly to adjust the edges of
the inverse video.
Use the raster dimensions given
in
the Specifications
in
Chapter
1.
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