LG 50PK550 Service Manual Download

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LGE Internal Use Only

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