42PG20-UA (CHASSIS:PU84A) — LG TV Service Manual (repair manual). Page 2

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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 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 X-RADIATION, Shock, Fire, or other Hazards. 
Do not modify the original design without permission of manufacturer.
General Guidance
An  lsolation  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  circuitary  that  may  be
inadvertently introduced during the service operation.
If any fuse (or Fusible Resistor) in this monitor is blown, replace
it with the same specified type.
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.
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  positioin,  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  esposed  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 sepcified, 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
CANADA: LG Electronics Canada, Inc. 550 Matheson
Boulevard East Mississauga, Ontario L4Z 4G3
USA      : LG Customer Interactive Center
P.O.Box 240007, 201 James Record Road Huntsville,
AL 35824
Digital TV Hotline  1-800-243-0000
1.5 Kohm/10W
To Instrument's
Good Earth Ground
such as WATER PIPE,
AC Volt-meter
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