LG PF-52A70 Service Manual page 15

¡ RF AGC (Auto Gain Control) Adjustment
Test Point : J104/ J106
Adjust : VRI1 / VRP1
The RF AGC control (VRI1/ VRP1 ) was aligned at the time of
manufacture for optimum performance over a wide range
conditions. Readjust of VRI1/ VRP1 should not be necessary
unless unusual local conditions exist, such as:
1) Channel interference in a CATV system.
2) Picture bending and/or color beats, which are unusually
due to excessive RF signal input when the receiver is too
close to a transmitting tower or when the receiver is
connected to an antenna distribution system where the
RF signal has been amplified. In this case, the input signal
should be attenuated(with pad or filter) to a satisfactory
level.
3) Picture noise caused by "broadcast noise" or weak signal.
If the broadcast is "clean" and the RF signal is at least
1mV(60dBuV), the picture will be noise free in any area.
Adjusting the VRI1/ VRP1 (RF AGC) control to one end of
rotation will usually cause a relatively poor signal to noise
ratio;
Adjusting to the other end of rotation will usually cause a
degradation of over load capabilities resulting in color beats
or adjacent channel reference.
For best results, adjust the VRI1/ VRP1 control while
performing on all over local channels, or the voltage at J150/
J151 will be 6.0¡ 0.1Vdc in RF level 60¡ 1dBuV.
¡ High Voltage Stabilization Adjustment
J67 (on Deflection Board)
Test Point :
VR402
Adjust :
1) Tune the TV set to receive a digital pattern.
2) Set contrast to 100%, brightness and color to 50%
respectively.
3) Adjust VR402 on the deflection board so that the DC
voltmeter may be read 4.0¡ 0.1Vdc.
¡ Vertical/Horizontal Size Adjustment
Test Point : Observing Display
Adjust : VR301 (Vertical Size)
VR401 (Horizontal Size)
1) Tune the TV set to receive a digital pattern.
2) Set contrast to 100%, brightness and color to 50%
respectively.
3) Adjust VR301 on the deflection board so that the circle of
the digital pattern may be located within the effective
screen on the TV screen.
4) Adjust VR401 on the deflection board so that the circle of
the digital pattern looks like exact circle.
¡ Cut-off Adjustment
NOTE : This adjustment should be performed after
warming up for 15 minutes at least.
Test Point :
Adjust :
1) Set VR902R, 902G, 902B on CRT Boards to the
mechanical center position.
2) Tune the TV set to receive white pattern of PAL
standard signal.
3) Press OK button on Control Board continuously and
INPUT(blue) button on remote controller for obtaining a
horizontal line on the middle of TV screen.
4) Turn VR902R, 902G, 902B counterclockwise and set it to
the minimum position.
5) Turn VR902R, 902G, 902B clockwise slowly to appear a
horizontal line.
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Observing Display
VR902R, 902G, 902B (Cut-off)