42LB9RTA (CHASSIS:LP7BB) - LG TV Service Manual (repair manual)

BEFORE SERVICING THE CHASSIS,
READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

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Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts are identified by      in the
Schematic Diagram and Exploded View. 
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.

An  isolation Transformer should always be used during the
servicing of a receiver whose chassis is not isolated from the AC
power line. Use a transformer of adequate power rating as this
protects the technician from accidents resulting in personal injury
from electrical shocks.

It will also protect the receiver and it's components from being
damaged by accidental shorts of the circuitry that may be
inadvertently introduced during the service operation.

If any fuse (or Fusible Resistor) in this TV receiver is blown,
replace it with the specified.

When replacing a high wattage resistor (Oxide Metal Film Resistor,
over 1W), keep the resistor 10mm away from PCB.

Keep wires away from high voltage or high temperature parts.

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
shock. 

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
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 1MΩ and 5.2MΩ. 
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.

(See below Figure) 

Plug the AC cord directly into the AC outlet.

Do not use a line Isolation Transformer during this check.
Connect 1.5K/10watt resistor in parallel with a 0.15uF capacitor
between a known good earth ground (Water Pipe, Conduit, etc.)
and the exposed metallic parts.
Measure the AC voltage across the resistor using AC voltmeter
with 1000 ohms/volt or more sensitivity.
Reverse plug the AC cord into the AC outlet and repeat AC voltage
measurements for each exposed metallic part. Any voltage
measured must not exceed 0.75 volt RMS which is corresponds to
0.5mA.
In case any measurement is out of the limits specified, there is
possibility of shock hazard and the set must be checked and
repaired before it is returned to the customer.

1.5 Kohm/10W

To Instrument's
exposed 
METALLIC PARTS

Good Earth Ground
such as WATER PIPE,
CONDUIT etc.

AC Volt-meter

0.15uF

RISK OF EXPLOSION IF BATTERY
IS REPLACED BY AN INCORRECT
TYPE. DISPOSE OF USED
BATTERIES ACCORDING TO THE
INSTRUCTIONS

Lithiumbatteri - Eksplosionsfare ved
fejlagtig hándtening. Udskiftning má
kun ske med batteri at samme
fabrikat og type. Levér det brugte
batteri tilbage til leverandoren

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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  precautions.
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
explosion 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  easily
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
damage 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.
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

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
exposure 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 solder

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
electrically  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 material
to  the  chassis  or  circuit  assembly  into  which  the  device  will  be
installed.
CAUTION: Be sure no power is applied to the chassis or circuit,
and observe all other safety precautions.

8.  Minimize  bodily  motions  when  handling  unpackaged

replacement  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
sufficient to damage an ES device.)

General Soldering Guidelines
1.  Use a grounded-tip, low-wattage soldering iron and appropriate

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 1.25cm) 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
component 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.