LG 49UF77 Series, Service Manual

- 4 -

LGE Internal Use Only

Copyright  © 

  LG Electronics. Inc. All rights reserved.

Only for training and service purposes

SERVICING PRECAUTIONS

CAUTION: Before servicing receivers covered by this service 

manual and its supplements and addenda, read and follow the 

SAFETY PRECAUTIONS

 on page 3 of this publication.

NOTE

: If unforeseen circumstances create conflict between the 

following servicing precautions and any of the safety precautions 

on page 3 of this publication, always follow the safety precau-

tions. Remember: Safety First.

General Servicing Precautions

1.  Always unplug the receiver AC power cord from the AC power 

source before;

a.  Removing or reinstalling any component, circuit board 

module or any other receiver assembly.

b.  Disconnecting or reconnecting any receiver electrical plug 

or other electrical connection.

c.  Connecting a test substitute in parallel with an electrolytic 

capacitor in the receiver.

CAUTION

: A wrong part substitution or incorrect polarity 

installation of electrolytic capacitors may result in an explo-

sion hazard.

2.  Test high voltage only by measuring it with an appropriate 

high voltage meter or other voltage measuring device (DVM, 

FETVOM, etc) equipped with a suitable high voltage probe.

Do not test high voltage by "drawing an arc".

3.  Do not spray chemicals on or near this receiver or any of its 

assemblies.

4.  Unless specified otherwise in this service manual, clean 

electrical contacts only by applying the following mixture to the 

contacts with a pipe cleaner, cotton-tipped stick or comparable 

non-abrasive applicator; 10 % (by volume) Acetone and 90 % 

(by volume) isopropyl alcohol (90 % - 99 % strength)

CAUTION

: This is a flammable mixture.

Unless specified otherwise in this service manual, lubrication 

of contacts in not required.

5.  Do not defeat any plug/socket B+ voltage interlocks with which 

receivers covered by this service manual might be equipped.

6.  Do not apply AC power to this instrument and/or any of its 

electrical assemblies unless all solid-state device heat sinks 

are correctly installed.

7.  Always connect the test receiver ground lead to the receiver 

chassis ground before connecting the test receiver positive 

lead.

Always remove the test receiver ground lead last.

8.  Use with this receiver only the test fixtures specified in this 

service manual.

CAUTION

: Do not connect the test fixture ground strap to any 

heat sink in this receiver.

Electrostatically Sensitive (ES) Devices

Some semiconductor (solid-state) devices can be damaged eas-

ily by static electricity. Such components commonly are called 

Electrostatically Sensitive (ES) Devices. Examples of typical ES 

devices are integrated circuits and some field-effect transistors 

and semiconductor “chip” components. The following techniques 

should be used to help reduce the incidence of component dam-

age caused by static by static electricity.

1.  Immediately before handling any semiconductor component or 

semiconductor-equipped assembly, drain off any electrostatic 

charge on your body by touching a known earth ground. Alter-

natively, obtain and wear a commercially available discharg-

ing wrist strap device, which should be removed to prevent 

potential shock reasons prior to applying power to the unit 

under test.

2.  After removing an electrical assembly equipped with ES 

devices, place the assembly on a conductive surface such as 

aluminum foil, to prevent electrostatic charge buildup or expo-

sure of the assembly.

3.  Use only a grounded-tip soldering iron to solder or unsolder 

ES devices.

4.  Use only an anti-static type solder removal device. Some sol-

der removal devices not classified as “anti-static” can generate 

electrical charges sufficient to damage ES devices.

5.  Do not use freon-propelled chemicals. These can generate 

electrical charges sufficient to damage ES devices.

6.  Do not remove a replacement ES device from its protective 

package until immediately before you are ready to install it. 

(Most replacement ES devices are packaged with leads elec-

trically shorted together by conductive foam, aluminum foil or 

comparable conductive material).

7.  Immediately before removing the protective material from the 

leads of a replacement ES device, touch the protective mate-

rial to the chassis or circuit assembly into which the device will 

be installed.

CAUTION

: Be sure no power is applied to the chassis or cir-

cuit, and observe all other safety precautions.

8.  Minimize bodily motions when handling unpackaged replace-

ment ES devices. (Otherwise harmless motion such as the 

brushing together of your clothes fabric or the lifting  of your 

foot from a carpeted floor can generate static electricity suf

-

ficient to damage an ES device.)

General Soldering Guidelines

1.  Use a grounded-tip, low-wattage soldering iron and appropri-

ate tip size and shape that will maintain tip temperature within 

the range or 500 °F to 600 °F.

2.  Use an appropriate gauge of RMA resin-core solder composed 

of 60 parts tin/40 parts lead.

3. Keep the soldering iron tip clean and well tinned.

4.  Thoroughly clean the surfaces to be soldered. Use a mall wire-

bristle (0.5 inch, or 1.25 cm) brush with a metal handle.

Do not use freon-propelled spray-on cleaners.

5.  Use the following unsoldering technique

a.  Allow the soldering iron tip to reach normal temperature. 

(500 °F to 600 °F)

b. Heat the component lead until the solder melts.

c.  Quickly draw the melted solder with an anti-static, suction-

type solder removal device or with solder braid.

CAUTION: Work quickly to avoid overheating the circuit 

board printed foil.

6.  Use the following soldering technique.

a.  Allow the soldering iron tip to reach a normal temperature 

(500 °F to 600 °F)

b.  First, hold the soldering iron tip and solder the strand 

against the component lead until the solder melts.

c.  Quickly move the soldering iron tip to the junction of the 

component lead and the printed circuit foil, and hold it there 

only until the solder flows onto and around both the compo

-

nent lead and the foil.

CAUTION

: Work quickly to avoid overheating the circuit 

board printed foil.

d.  Closely inspect the solder area and remove any excess or 

splashed solder with a small wire-bristle brush.