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General Guidance
An is olation 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 1 W), keep the resistor 10 mm away
from PCB.
Keep wires away from high voltage or high temperature
parts.
Before returning the receiver to the customer,
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.
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 1
MΩ and 5.2 MΩ.
When the exposed metal has no return path to the
SAFETY PRECAUTIONS
chassis the reading must be infinite.
Another 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 1.5 K / 10 watt resistor in parallel with a 0.15
uF 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
1.5 mA.
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.
3
Leakage Current Hot Check circuit
Copyright ⓒ 2017 LG Electronics. Inc. All right reserved.
Only for training and service purposes
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