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MODEL : 37LC2D / 42LC2D


CONTENTS .............................................................................................. 2

SAFETY PRECAUTIONS ..........................................................................3

SPECIFICATION ........................................................................................6

ADJUSTMENT INSTRUCTION ...............................................................12

TROUBLE SHOOTING ............................................................................19

BLOCK DIAGRAM...................................................................................25

EXPLODED VIEW .................................................................................. 26

REPLACEMENT PARTS LIST ............................................................... 30

SVC. SHEET ...............................................................................................


Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts are identified by in the
Schematic Diagram and Replacement Parts List.
It is essential that these special safety parts should be replaced with the same components as recommended in this manual to prevent
Shock, Fire, or other Hazards.
Do not modify the original design without permission of manufacturer.

General Guidance Leakage Current Hot Check (See below Figure)
Plug the AC cord directly into the AC outlet.
An isolation Transformer should always be used during the
servicing of a receiver whose chassis is not isolated from the AC Do not use a line Isolation Transformer during this check.
power line. Use a transformer of adequate power rating as this Connect 1.5K/10watt resistor in parallel with a 0.15uF capacitor
protects the technician from accidents resulting in personal injury between a known good earth ground (Water Pipe, Conduit, etc.)
from electrical shocks. and the exposed metallic parts.
Measure the AC voltage across the resistor using AC voltmeter
It will also protect the receiver and it's components from being with 1000 ohms/volt or more sensitivity.
damaged by accidental shorts of the circuitry that may be Reverse plug the AC cord into the AC outlet and repeat AC voltage
inadvertently introduced during the service operation. measurements for each exposed metallic part. Any voltage
measured must not exceed 0.75 volt RMS which is corresponds to
If any fuse (or Fusible Resistor) in this TV receiver is blown, 0.5mA.
replace it with the specified. In case any measurement is out of the limits specified, there is
possibility of shock hazard and the set must be checked and
When replacing a high wattage resistor (Oxide Metal Film Resistor, repaired before it is returned to the customer.
over 1W), keep the resistor 10mm away from PCB.
Leakage Current Hot Check circuit
Keep wires away from high voltage or high temperature parts.
AC Volt-meter
Before returning the receiver to the customer,

always perform an AC leakage current check on the exposed
metallic parts of the cabinet, such as antennas, terminals, etc., to
be sure the set is safe to operate without damage of electrical Good Earth Ground
shock. such as WATER PIPE,
To Instrument's CONDUIT etc.
Leakage Current Cold Check(Antenna Cold Check) exposed
With the instrument AC plug removed from AC source, connect an
electrical jumper across the two AC plug prongs. Place the AC
switch in the on position, connect one lead of ohm-meter to the AC 1.5 Kohm/10W
plug prongs tied together and touch other ohm-meter lead in turn to
each exposed metallic parts such as antenna terminals, phone
jacks, etc.
If the exposed metallic part has a return path to the chassis, the
measured resistance should be between 1M and 5.2M.
When the exposed metal has no return path to the chassis the
reading must be infinite.
An other abnormality exists that must be corrected before the
receiver is returned to the customer.

CAUTION: Before servicing receivers covered by this service unit under test.
manual and its supplements and addenda, read and follow the 2. After removing an electrical assembly equipped with ES
SAFETY PRECAUTIONS on page 3 of this publication. devices, place the assembly on a conductive surface such as
NOTE: If unforeseen circumstances create conflict between the aluminum foil, to prevent electrostatic charge buildup or
following servicing precautions and any of the safety precautions on exposure of the assembly.
page 3 of this publication, always follow the safety precautions. 3. Use only a grounded-tip soldering iron to solder or unsolder ES
Remember: Safety First. devices.
4. Use only an anti-static type solder removal device. Some solder
General Servicing Precautions removal devices not classified as "anti-static" can generate
1. Always unplug the receiver AC power cord from the AC power electrical charges sufficient to damage ES devices.
source before; 5. Do not use freon-propelled chemicals. These can generate
a. Removing or reinstalling any component, circuit board electrical charges sufficient to damage ES devices.
module or any other receiver assembly. 6. Do not remove a replacement ES device from its protective
b. Disconnecting or reconnecting any receiver electrical plug or package until immediately before you are ready to install it.
other electrical connection. (Most replacement ES devices are packaged with leads
c. Connecting a test substitute in parallel with an electrolytic electrically shorted together by conductive foam, aluminum foil
capacitor in the receiver. or comparable conductive material).
CAUTION: A wrong part substitution or incorrect polarity 7. Immediately before removing the protective material from the
installation of electrolytic capacitors may result in an leads of a replacement ES device, touch the protective material
explosion hazard. to the chassis or circuit assembly into which the device will be
2. Test high voltage only by measuring it with an appropriate high CAUTION: Be sure no power is applied to the chassis or circuit,
voltage meter or other voltage measuring device (DVM, and observe all other safety precautions.
FETVOM, etc) equipped with a suitable high voltage probe. 8. Minimize bodily motions when handling unpackaged
Do not test high voltage by "drawing an arc". replacement ES devices. (Otherwise harmless motion such as
3. Do not spray chemicals on or near this receiver or any of its the brushing together of your clothes fabric or the lifting of your
assemblies. foot from a carpeted floor can generate static electricity
4. Unless specified otherwise in this service manual, clean sufficient to damage an ES device.)
electrical contacts only by applying the following mixture to the
contacts with a pipe cleaner, cotton-tipped stick or comparable General Soldering Guidelines
non-abrasive applicator; 10% (by volume) Acetone and 90% (by 1. Use a grounded-tip, low-wattage soldering iron and appropriate
volume) isopropyl alcohol (90%-99% strength) tip size and shape that will maintain tip temperature within the
CAUTION: This is a flammable mixture. range or 500 F to 600 F.
Unless specified otherwise in this service manual, lubrication of 2. Use an appropriate gauge of RMA resin-core solder composed
contacts in not required. of 60 parts tin/40 parts lead.
5. Do not defeat any plug/socket B+ voltage interlocks with which 3. Keep the soldering iron tip clean and well tinned.
receivers covered by this service manual might be equipped. 4. Thoroughly clean the surfaces to be soldered. Use a mall wire-
6. Do not apply AC power to this instrument and/or any of its bristle (0.5 inch, or 1.25cm) brush with a metal handle.
electrical assemblies unless all solid-state device heat sinks are Do not use freon-propelled spray-on cleaners.
correctly installed. 5. Use the following unsoldering technique
7. Always connect the test receiver ground lead to the receiver a. Allow the soldering iron tip to reach normal temperature.
chassis ground before connecting the test receiver positive (500 F to 600 F)
lead. b. Heat the component lead until the solder melts.
Always remove the test receiver ground lead last. c. Quickly draw the melted solder with an anti-static, suction-
8. Use with this receiver only the test fixtures specified in this type solder removal device or with solder braid.
service manual. CAUTION: Work quickly to avoid overheating the
CAUTION: Do not connect the test fixture ground strap to any circuitboard printed foil.
heat sink in this receiver. 6. Use the following soldering technique.
a. Allow the soldering iron tip to reach a normal temperature
Electrostatically Sensitive (ES) Devices (500 F to 600 F)
Some semiconductor (solid-state) devices can be damaged easily b. First, hold the soldering iron tip and solder the strand against
by static electricity. Such components commonly are called the component lead until the solder melts.
Electrostatically Sensitive (ES) Devices. Examples of typical ES c. Quickly move the soldering iron tip to the junction of the
devices are integrated circuits and some field-effect transistors and component lead and the printed circuit foil, and hold it there
semiconductor "chip" components. The following techniques only until the solder flows onto and around both the
should be used to help reduce the incidence of component component lead and the foil.
damage caused by static by static electricity. CAUTION: Work quickly to avoid overheating the circuit
1. Immediately before handling any semiconductor component or board printed foil.
semiconductor-equipped assembly, drain off any electrostatic d. Closely inspect the solder area and remove any excess or
charge on your body by touching a known earth ground. splashed solder with a small wire-bristle brush.
Alternatively, obtain and wear a commercially available
discharging wrist strap device, which should be removed to
prevent potential shock reasons prior to applying power to the

IC Remove/Replacement
Some chassis circuit boards have slotted holes (oblong) through Circuit Board Foil Repair
which the IC leads are inserted and then bent flat against the Excessive heat applied to the copper foil of any printed circuit
circuit foil. When holes are the slotted type, the following technique board will weaken the adhesive that bonds the foil to the circuit
should be used to remove and replace the IC. When working with board causing the foil to separate from or "lift-off" the board. The
boards using the familiar round hole, use the standard technique following guidelines and procedures should be followed whenever
as outlined in paragraphs 5 and 6 above. this condition is encountered.

Removal At IC Connections
1. Desolder and straighten each IC lead in one operation by gently To repair a defective copper pattern at IC connections use the
prying up on the lead with the soldering iron tip as the solder following procedure to install a jumper wire on the copper pattern
melts. side of the circuit board. (Use this technique only on IC
2. Draw away the melted solder with an anti-static suction-type connections).
solder removal device (or with solder braid) before removing the
IC. 1. Carefully remove the damaged copper pattern with a sharp
Replacement knife. (Remove only as much copper as absolutely necessary).
1. Carefully insert the replacement IC in the circuit board. 2. carefully scratch away the solder resist and acrylic coating (if
2. Carefully bend each IC lead against the circuit foil pad and used) from the end of the remaining copper pattern.
solder it. 3. Bend a small "U" in one end of a small gauge jumper wire and
3. Clean the soldered areas with a small wire-bristle brush. carefully crimp it around the IC pin. Solder the IC connection.
(It is not necessary to reapply acrylic coating to the areas). 4. Route the jumper wire along the path of the out-away copper
pattern and let it overlap the previously scraped end of the good
"Small-Signal" Discrete Transistor copper pattern. Solder the overlapped area and clip off any
Removal/Replacement excess jumper wire.
1. Remove the defective transistor by clipping its leads as close as
possible to the component body. At Other Connections
2. Bend into a "U" shape the end of each of three leads remaining Use the following technique to repair the defective copper pattern
on the circuit board. at connections other than IC Pins. This technique involves the
3. Bend into a "U" shape the replacement transistor leads. installation of a jumper wire on the component side of the circuit
4. Connect the replacement transistor leads to the corresponding board.
leads extending from the circuit board and crimp the "U" with
long nose pliers to insure metal to metal contact then solder 1. Remove the defective copper pattern with a sharp knife.
each connection. Remove at least 1/4 inch of copper, to ensure that a hazardous
condition will not exist if the jumper wire opens.
Power Output, Transistor Device 2. Trace along the copper pattern from both sides of the pattern
Removal/Replacement break and locate the nearest component that is directly
1. Heat and remove all solder from around the transistor leads. connected to the affected copper pattern.
2. Remove the heat sink mounting screw (if so equipped). 3. Connect insulated 20-gauge jumper wire from the lead of the
3. Carefully remove the transistor from the heat sink of the circuit nearest component on one side of the pattern break to the lead
board. of the nearest component on the other side.
4. Insert new transistor in the circuit board. Carefully crimp and solder the connections.
5. Solder each transistor lead, and clip off excess lead. CAUTION: Be sure the insulated jumper wire is dressed so the
6. Replace heat sink. it does not touch components or sharp edges.

Diode Removal/Replacement
1. Remove defective diode by clipping its leads as close as
possible to diode body.
2. Bend the two remaining leads perpendicular y to the circuit
3. Observing diode polarity, wrap each lead of the new diode
around the corresponding lead on the circuit board.
4. Securely crimp each connection and solder it.
5. Inspect (on the circuit board copper side) the solder joints of
the two "original" leads. If they are not shiny, reheat them and if
necessary, apply additional solder.
Fuse and Conventional Resistor
1. Clip each fuse or resistor lead at top of the circuit board hollow
2. Securely crimp the leads of replacement component around
notch at stake top.
3. Solder the connections.
CAUTION: Maintain original spacing between the replaced
component and adjacent components and the circuit board to
prevent excessive component temperatures.

NOTE : Specifications and others are subject to change without notice for improvement.

1. Application range 3. Test method
This specification is applied to LB61A chassis.
3.1 Performance : LGE TV test method followed
2. Requirement for Test 3.2 Demanded other specification
Testing for standard of each part must be followed in below Safety : CB Specification
condition. EMC : CISPR 13 Specification

(1) Temperature : 25