Vertical Linearity; Focus; Dynamic Focus - Zenith ZCM-1490 Service Manual

To adjust the 480-line mode sub-size:
1. Use appropriate software to fill the screen in the
480-line mode.
2. Adjust sub-size control R2124 for a display
height of approximately 195 mm ± 2 mm (7.67
inches).
To adjust the 400-line mode sub-size:
1. Use appropriate software to fill the screen in the
400-line mode.
2. Adjust sub-size control R2170 for a display
height of approximately 195 mm ±2 mm (7.67
inches).
To adjust the 3So-line mode sub-size:
1. Use appropriate software to fill the screen in the
350-line mode.
2. Adjust sub-size control R2158 for a display
height of approximately 195 mm ±2 mm (7.67
inches).
Vertical Linearity
The vertical linearity control (R21 07) adjusts the verti-
cal scanning for evenly spaced scanning lines on the
display. To adjust the vertical linearity:
1. Display a crosshatch pattern. (Use appropriate
software to generate this pattern in the 480-line
mode.)
2. Adjust R2107 so that the horizontal lines of the
crosshatch pattern are evenly spaced from the
top to the bottom of the display. The resulting
display will show minimal compression, crowd-
ing, or expansion of horizontal lines throughout
the display.
Focus
The focus control varies the focus voltage to sharpen
the display detail. To adjust focus:
1. Display a dot test pattern (refer to the
"Inspection and Preparation" section of Chapter
6 for the procedure). Alternatively, perform the
fill screen test using the capital Z.
2. Set the external brightness and contrast controls
to their detent positions.
3. Adjust the focus control (located on the high-
voltage resistor block) for the best overall focus.
Check the center, top center, bottom center, left
center, and right center areas of the display for
good focus.
4. Verify acceptable overall focus using the fill
screen test with such characters as @ and #. If
the focus is not fairly uniform throughout most of
the screen, perform the dynamic focus adjust-
ment.
NOTE: If the G2 control is adjusted after the focus
control has been adjusted, it may be necessary to
re-adjust the focus control.
Dynamic Focus
The dynamic focus circuitry varies the focus voltage
at the horizontal rate so that the voltage at the raster
edges is increased and the voltage at the center is
decreased. This results in a more uniform overall dis-
play focus. To adjust the dynamic focus control
(R7703):
1. Display a dot test pattern (refer to the
"Inspection and Preparation" section of Chapter
6 for the procedure). Alternatively, perform the
fill screen test using the capital Z.
2. Set the external brightness and contrast controls
to their detent positions.
Adjustments Page 4-7