LG 42PJ250, Service Manual

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LGE Internal Use Only

Copyright ©2010 LG Electronics Inc. All rights reserved. 
Only for training and service purposes

SAFETY PRECAUTIONS

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 X-RADIATION, Shock, Fire, or other Hazards. 
Do not modify the original design without permission of manufacturer.

General Guidance

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 monitor 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.

Due  to  high  vacuum  and  large  surface  area  of  picture  tube,
extreme care should be used in 

handling the Picture Tube.

Do not lift the Picture tube by it's Neck.

Leakage Current Cold Check(Antenna Cold Check)

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.

Leakage Current Hot Check 

(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.

Leakage Current Hot Check circuit

1.5 Kohm/10W

To Instrument's
exposed 
METALLIC PARTS

Good Earth Ground
such as WATER PIPE,
CONDUIT etc.

AC Volt-meter

IMPORTANT SAFETY NOTICE

0.15uF