Adjustment - LG CF-20/21S42EH Service Manual

Safety Precautions
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1. It is safe to adjust after using insulating transformer
between the power supply line and chassis input to
prevent the risk of electric shock and protect the
instrument.
2. Never disconnect leads while the TV receiver is on.
3. Don't short any portion of circuits while power is on.
4. The adjustment must be done by the correct appliances.
But this is changeable in view of productivity.
5. Unless otherwise noted, set the line voltage to
230Vac!10%, 50Hz.
Test Equipment required
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1. RF signal generator (with pattern generator)
2. DC Power Supply
3. Multimeter (volt meter)
4. Oscilloscope
5. Color analyzer
RF AGC (Automatic Gain Control) Adjustment
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Test Point : AGC TP (J29)
Adjust : Remote Control
The RF AGC was aligned at the time of manufacture for
optimum performance over a wide range conditions.
Readjustment of RF AGC 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 (60dBu), the picture will be noise free in any area.
Adjusting RF AGC 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 interference.

Adjustment

1. Connect RF signal (65dB!1dB) and turn on the TV.
2. Press OK buttons on TV set and Remote Controller at the
same time to get into SVC mode.
3. Press Channel UP/DOWN button on the Remote Controller
several times to find AGC ??.
4. Press Volume UP/DOWN button until the AGC Voltage is
the same as the Table below.
5. Press OK( ) button to memorize the data.
V
ADJUSTMENT
TUNER
AGC Voltage
Screen Voltage Adjustment
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Test Point
Adjust
1) Tune the TV set to receive a digital pattern.
2) Press PSM (RED) button on remote controller. (standard
picture)
3) Connect the probe of oscilloscope to the RK (Red
Cathode) of CPT Board.
4) Adjust Screen Volume of FBT so that the waveform is the
same as below figure.
The waveform of RK(Red Cathode) of CPT Board
Focus Adjustment
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NOTE: This adjustment should be performed after warming
Test Point
Adjust
1) Tune the TV set to receive an inactive channel station.
2) Adjust the Focus control of FBT for best overall focus.
- 10 -
6700VPF009D
2.6 ! 0.5V
: RK (Red Cathode of CPT Board)
: Screen Control of FBT
Horizontal
FlyBack Time
up for 10 minutes.
: Observing Display
: Focus control of FBT
6700VPF003B
2.7 ! 0.5V
Black level
140Vp-p
White level
GND for dc