Service manual

STP 11-25R13-SM-TG
3 - 30
Performance Steps
(1) Inject a sweep generator signal into the intermediate frequency (IF) amplifier input tuner
and monitor the signal at the video detector output on an oscilloscope. If the overall
response is good through the RF tuner and IF stage, the trouble is probably in the video
amplifier.
(2) Check the video amplifier circuit by applying a 1 V square wave to its input.
( a) Monitor the output on an oscilloscope, checking the overall response of the video
amplifiers, to include CONTRAST and BRIGHTNESS controls.
( b) If square waves pass through to the CRT, the video amplifier is good.
5. Replace, repair, or adjust faulty component.
a. Perform preliminary procedures before proceeding with adjustments.
(1) With power removed, remove the back of the receiver/monitor and then plug the cord into
an AC outlet.
(2) Connect color bars from the VTSG through a 75-ohm coaxial cable to an input connection;
connect a 75-ohm terminator on the loop-through connection.
(3) Set all front panel toggle and lever switches to the up position. Set all variable controls to
the preset position.
(4) Allow at least 30 minutes warm-up time at 25 +/-5 degrees Celsius.
(5) Decrease room lighting to semidarkness.
b. Adjust color purity.
(1) Display a 100 IRE or 100 percent flat field signal from the VTSG.
(2) Turn OFF the green (G) and blue (B) SCREEN switches on the receiver/monitor.
(3) Check for an uniform red display screen. For any impurity observed, use a hand-held
degaussing coil to demagnetize the surrounding metal parts.
( a) Plug the degaussing coil into an AC outlet; while standing no closer than 6 feet in
front of the receiver/monitor, turn ON the coil.
( b) Slowly rotate the coil in a circular motion until the coil is approximately 3 inches in
front of the receiver/monitor.
( c) Continue the circular motion around each side, across the top, and back to the front
of the receiver/monitor.
( d) While standing in front of the receiver/monitor, slowly move the coil at least 6 feet
from the receiver/monitor.
( e) Rotate the coil to a right angle of the receiver/monitor; then turn OFF and unplug the
coil.
(4) Turn OFF the red (R) SCREEN switch and turn ON the G SCREEN switch.
(5) Check for an uniform green screen.
(6) Turn OFF the G SCREEN switch and turn on the B SCREEN switch.
(7) Check for an uniform blue screen.
(8) Turn ON the R and G SCREEN switches.
c. Adjust H and V CENTERING.
(1) Display a crosshatch signal from the VTSG.
(2) Turn OFF the R and B SCREEN switches to display a green screen crosshatch pattern.
(3) Set the SIZE switch to UNDERSCAN.
(4) If the VTSG has H and V CONVERGENCE position controls, set these controls to properly
center the crosshatch pattern.
( a) Position the vertical lines at the left and right sides of the display equal distance from
the edges of video blanking (not the bezel or screen edges).
( b) Position the horizontal lines at the top and bottom sides of the display equal distance
from the edges of video blanking.
(5) Set the SIZE switch to the NORMAL position.
(6) Place the linearity graticule directly over the viewing screen. After centering the graticule
over the screen, tape the graticule in a few places to hold it in position.
(7) Place an incandescent light source 2 feet in front of and aimed at the center of the screen.
(8) Adjust H and V CENTERING to center the display in the graticule area.
d. Adjust H and V SIZE.