LG PF-43A20, Service Manual

Page: 3 / 59

- 3 -
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 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 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.
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.
X-RAY Radiation
Warning:
To determine the presence of high voltage, use an accurate
high impedance HV meter.
Adjust brightness, color, contrast controls to minimum.
Measure the high voltage.
The meter reading should indicate
23.5
¡
1.5KV: 14-19 inch, 26
¡
1.5KV: 19-21 inch,
29.0
¡
1.5KV: 25-29 inch, 30.0
¡
1.5KV: 32 inch
If the meter indication is out of tolerance, immediate service
and correction is required to prevent the possibility of
premature component failure.
Insulation Resistance Testing
Examine the area surrounding the repaired location for damage
or deterioration, Observe that screws, parts and wires have
been returned to original positions. Afterwards, perform the
following tests and confirm the specified values in order to
verity compliance with safety standards.
Requirements of the Electricity regulations 1997 and
AS/NZS3760 : 1996
All products that are serviced must have a safety test carried
out in accordance with AS/NZS 3760 : 1996.
This equipment is double insulated so the following test should
be carried out.
Testing Equipment Required :
An insulation resistance meter with the following characteristics.
a) A measuring circuit isolated from earth
b) Nominal measuring voltage 500V DC
c) Accuracy Class 5 or better (Class 5 = accuracy of 5%)
Insulation resistance test.
During this test the power switch must in the "ON" position.
For the purpose of this test, small exposed metal parts such as
nameplates, screws or rivets which are fixed or attached to
non-conductive material in such a manner that they cannot
become live, even in the event of a failure of internal insulation,
are not required to be tested.
Confirm that the insulation resistance between the power plug
prongs and externally exposed parts of the unit (metal case,
bottom cover, RF terminals, antenna terminals, video and audio
output and input terminals, microphone jacks, earphone jacks,
oxtension speaker sockets, etc) has a minimum resistance of
1M
§
.
The source of X-RAY RADIATION in this TV receiver is the
High Voltage Section and the Picture Tube.
For continued X-RAY RADIATION protection, the
replacement tube must be the same type tube as specified in
the Replacement Parts List.
VIDEO
AUDIO
75 Ω L
R
IN
OUT
L LE EG GE EN ND D ::
¤
Any switch to be "ON"
during tests
¤Ł
Test active and neutral to
exposed metal parts
Insulation resistance
meter
IMPORTANT SAFETY NOTICE