Adjustment - LG PF-52A70 Service Manual

§ Safety Precautions
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. Don't operate the TV with a non-moving picture for any
more than 10 minutes as damage may occur to the phosphor
on the CRT.
5. The adjustment must be done by the appropriate appliances
and the correct step.
6. Unless otherwise noted, set the line voltage to 220V ¡ 10%,
50Hz.
§ T est Equipment required
1. VIF sweep generator
2. Color bar/cross-hatch pattern generator
3. DC power supply
4. Digital multi-meter
5. Color analyzer
Preparation for VCO & AFT Adjustment
1. Connect the measuring equipment to the TV as shown in
Fig.1.
2. Set RF output level of Sweep S.G (Signal Generator) to
90dBuV.
3. Set Alignment Scope, Volts/Div to 100mV (VCO) or
1V(AFT), AC/DC switch to AC, Line/Ext switch to Ext.
DC POWER
SUPPLY
+ -
12 0.1V
SWEEP S.G.
with Marker
(VP-8800G)
Alignment
Scope
Fig.1 : Connection Diagram of Equipment for
VCO & AFT Adjustment.
NOTE :
: PIP Board
ADJUSTMENT INSTRUCTIONS
To TP2/ TP21
3.3K
TP24
1K
4.7K VCO : ON
AFT : OFF
0.01µF
To TP1/ TP20
(VCO)
To TP3/ TP22
(AFT)
TP23
¡ Main VCO (Voltage Controlled Oscillator)

Adjustment

Test Point :
Adjust :
1) Turn on DC power supply.
2) Adjust LI6 so that the waveform of Oscilloscope becomes
2.6V DC.
¡ PIP VCO (Voltage Controlled Oscillator)
Adjustment
Test Point :
Adjust :
1) Turn on DC power supply.
2) Adjust Video Detector Coil ( LP8 ) so that a waveform on
Alignment Scope is the same as below Fig.2.
A B C
Fig.2 : VCO waveform on Alignment Scope
¡ AFT (Auto Fine Tuning) Adjustment
Test Point :
Adjust :
1) Turn on DC power supply.
2) Adjust IF AFT coil (LP5 ) so that 38.0MHz (Vc) point may
be centered as Fig.3.
Fig.3: AFT waveform on Alignment Scope
- 14 -
TP3
LI6
2.6V
GND
TP22
LP8
D E F G
TP23
LP5
A
B
A : 30.0MHz
B : 31.5MHz
C : 32.84MHz
D : 36.8MHz
E : 38.0MHz
F : 39.5MHz
G : 40.25MHz
A: 36.8MHz
B: 38.0MHz