HP 9020 User Manual

3-12 Testing and Troubleshooting
98760A Display Color Alignment
A critical aspect of 98760A operation is the correct alignment of the brightness levels of the primary
colors. Incorrect alignment can lead to a variety of problems including high failure rate, degraded
performance, visible retrace lines, display not meeting specifications, lower intensities not visible
and customer complaints that two 98760A displays differ in appearance. This section contains
information
needed to perform the adjustment as well as to determine when it must be done.
Overview of the Alignment Process
The 98760A has 16 steps of brightness (intensity) for each of the three primary colors, red, green
and blue. This makes possible 4096 different hues (16 times 16 times 16), but complicates the
adjustment process since
it is necessary to adjust the threshold of visibility as well as the brightness
of the highest step. Each primary color has
one potentiometer (the clamp pot) for the threshold of
visibility
and one pot (the gain pot) for the highest step (step 15). Note that the highest step equals
the threshold plus the gain.
In addition, there is one pot for the screen grid.
When Needed
The intensity alignment must be performed whenever the video board, sweep board or CRT Iyoke
assembly are replaced. It should be performed even if the display looks acceptable to the eye, since
reliability
is significantly diminished in an incorrectly aligned display even if the CRT looks accept-
able.
In addition, the intensity adjustment should be made whenever a given graphics output differs
from display to display.
Required Equipment
The following equipment is required for 98760A color alignment:
• Voltmeter
• PHOTO DYNE 19XE Radiometer
• CRT Alignment Tool (PN 8710-1388)
•
System Functional Test Discs (PN 09020-10010)
Test Conditions
The conditions under which the adjustment is made can affect the results. Here is how to optimize
conditions for the most accurate results.
Light
Direct sun or light from a window can result in erroneous readings. Position the 98760A to face
directly away from the nearest windows or cover them with opaque drapes. The CRT bezel
decreases sensitivity to ambient light, so
it must be installed. The alignment procedure assumes that
the bezel
is in place.
Temperature
The temperature should be maintained at 65 to 75 degrees fahrenheit during the adjustment
process, with the unit powered
on for at least 10 minutes beforehand. If the unit was brought from a
location with a different temperature,
it should be powered on for a proportionately longer time.
(Storage of the unit
at - 40°C to + 75°C is possible without exceeding specifications. Stabilization
time should be adjusted accordingly.)
09020-90037, rev: 1185

HP 9020 Specifications

General

Brand	HP
Model	9020
Category	Desktop
Language	English