LG 14LK20A Service Manual
14LK20A
SERVICE MANUAL
S49F614LK20A/
COLOR TELEVISION
Chassis No. SN-70A
MODEL
In the interests of user-safety (Required by safety regulations in some countries) the set should be restored to its
original condition and only parts identical to those specified should be used.
14LK20A
CONTENTS
Page
» ELECTRICAL SPECIFICATIONS......................................................................................................... 1
» IMPORTANT SERVICE SAFETY PRECAUTION ................................................................................2
» LOCATION OF USER'S CONTROL.....................................................................................................4
» INSTALLATION AND SERVICE INSTRUCTIONS ............................................................................... 5
» CHASSIS LAYOUT ............................................................................................................................ 10
» BLOCK DIAGRAM ..............................................................................................................................11
» DESCRIPTION OF SCHEMATIC DIAGRAMS ...................................................................................12
» SCHEMATIC DIAGRAMS .................................................................................................................. 13
» PRINTED WIRING BOARD ASSEMBLIES........................................................................................16
» REPLACEMENT PARTS LIST ........................................................................................................... 19
» PACKING OF THE SET ..................................................................................................................... 25
ELECTRICAL SPECIFICATIONS
POWER INPUT ....................................... 110-220 V AC 50/60 Hz
POWER RATING....................................................................63 W
PICTURE SIZE ............................................. 580cm2 (89.8sq inch)
CONVERGENCE............................................................. Magnetic
SWEEP DEFLECTION .....................................................Magnetic
FOCUS ............................................... Hi-Bi-Potential Electrostatic
INTERMEDIATE FREQUENCIES
Picture IF Carrier Frequency ..................................... 45.75 MHz
Sound IF Carrier Frequency ......................................41.25 MHz
Color Sub-Carrier Frequency..................................... 42.17 MHz
(Nominal)
AUDIO POWER
OUTPUT RATING.................................1.3W (at 10% distortion)
SPEAKER
SIZE .............................................................................. 9 x 5 cm
VOICE COIL IMPEDANCE............................. 16 ohm at 400 Hz
ANTENNA INPUT IMPEDANCE
VHF/UHF .................................................... 75 ohm Unbalanced
TUNING RANGES
VHF-Channels .............................................................. 2 thru 13
UHF-Channels ............................................................14 thru 69
CATV Channels ..........................................................1 thru 125
Specifications are subject to change without
prior notice.
SHARP CORPORATION
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14LK20A
IMPORTANT SERVICE SAFETY PRECAUTION
Ë
Service work should be performed only by qualified service technicians who are thoroughly
familiar with all safety checks and the servicing guidelines which follow:
WARNING
1. For continued safety, no modification of any circuit
should be attempted.
2. Disconnect AC power before servicing.
3. Semiconductor heat sinks are potential shock
hazards when the chassis is operating.
4. The chassis in this receiver has two ground systems
which are separated by insulating material. The nonisolated (hot) ground system is for the B+ voltage
regulator circuit and the horizontal output circuit. The
isolated ground system is for the low B+ DC voltages
and the secondary circuit of the high voltage
transformer.
To prevent electrical shock use an isolation
transformer between the line cord and power
receptacle, when servicing this chassis.
SERVICING OF HIGH VOLTAGE SYSTEM
AND PICTURE TUBE
When servicing the high voltage system,
remove the static charge by connecting a
10k ohm resistor in series with an insulated
wire (such as a test probe) between the picture tube ground and the anode lead. (AC
line cord should be disconnected from AC
outlet.)
1. Picture tube in this receiver employs integral
implosion protection.
2. Replace with tube of the same type number for
continued safety.
3. Do not lift picture tube by the neck.
4. Handle the picture tube only when wearing
shatterproof goggles and after discharging the high
voltage anode completely.
X-RADIATION AND HIGH VOLTAGE LIMITS
1. Be sure all service personnel are aware of the
procedures and instructions covering X-radiation. The
only potential source of X-ray in current solid state
TV receivers is the picture tube. However, the picture
tube does not emit measurable X-Ray radiation, if
the high voltage is as specified in the "High Voltage
Check" instructions.
It is only when high voltage is excessive that Xradiation is capable of penetrating the shell of the
picture tube including the lead in the glass material.
The important precaution is to keep the high voltage
below the maximum level specified.
2. It is essential that servicemen have available at all
times an accurate high voltage meter.
The calibration of this meter should be checked
periodically.
3. High voltage should always be kept at the rated value
−no higher. Operation at higher voltages may cause
a failure of the picture tube or high voltage circuitry
and;also, under certain conditions, may produce
radiation in exceeding of desirable levels.
4. When the high voltage regulator is operating properly
there is no possibility of an X-radiation problem. Every
time a color chassis is serviced, the brightness should
be tested while monitoring the high voltage with a
meter to be certain that the high voltage does not
exceed the specified value and that it is regulating
correctly.
5. Do not use a picture tube other than that specified or
make unrecommended circuit modifications to the
high voltage circuitry.
6. When trouble shooting and taking test measurements
on a receiver with excessive high voltage, avoid being
unnecessarily close to the receiver.
Do not operate the receiver longer than is necessary
to locate the cause of excessive voltage.
2
2
2
IMPORTANT SERVICE SAFETY PRECAUTION
(Continued)
14LK20A
BEFORE RETURNING THE RECEIVER
(Fire & Shock Hazard)
Before returning the receiver to the user, perform
the following safety checks.
1. Inspect all lead dress to make certain that leads are
not pinched or that hardware is not lodged between
the chassis and other metal parts in the receiver.
2. Inspect all protective devices such as non-metallic
control knobs, insulating materials, cabinet backs,
adjustment and compartment covers or shields,
isolation resistor-capacity networks, mechanical
insulators and etc.
3. To be sure that no shock hazard exists, check for
leakage current in the following manner.
• Plug the AC cord directly into a 1 10~120 volt AC outlet,
(Do not use an isolation transformer for this test).
• Using two clip leads, connect a 1.5k ohm, 10 watt
resistor paralleled by a 0.15µF capacitor in series with
all exposed metal cabinet parts and a known earth
ground, such as electrical conduit or electrical ground
connected to earth ground.
• Use an AC voltmeter having with 5000 ohm per volt,
or higher, sensitivity to measure the AC voltage drop
across the resistor.
• Connect the resistor connection to all exposed metal
parts having a return to the chassis (antenna, metal
cabinet, screw heads, knobs and control shafts,
escutcheon and etc.) and measure the AC voltage
drop across the resistor.
AII checks must be repeated with the AC ine cord
plug connection reversed. (If necessary, a nonpolarized adapter plug must be used only for the
purpose of completing these check.)
Any current measured must not exceed 0.5 milliamp.
Any measurements not within the limits outlined
above indicate of a potential shock hazard and
corrective action must be taken before returning the
instrument to the customer.
1.5k ohm
10W
0.15µF
TEST PROBE
TO EXPOSED
METAL PARTS
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CONNECT TO
KNOWN EARTH
GROUND
SAFETY NOTICE
Many electrical and mechanical parts in television
receivers have special safety-related characteristics.
These characteristics are often not evident from visual
inspection, nor can protection afforded by them be
necessarily increased by using replacement components
rated for higher voltage, wattage, etc.
Replacement parts which have these special safety
characteristics are identified in this manual; electrical
components having such features are identified by "å"
and shaded areas in the Replacement Parts Lists and
Schematic Diagrams.
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For continued protection, replacement parts must be
identical to those used in the original circuit. The use of
substitute replacement parts which do not have the same
safety characteristics as the factory recommended
replacement parts shown in this service manual, may
create shock, fire, X-radiation or other hazards.
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14LK20A
LOCATION OF USER'S CONTROL
4
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