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ⓒ
2020 LG Electronics. Inc. All right reserved. Only for training and service purposes
SAFETY PRECAUTIONS
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 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 M
Ω
and 5.2 M
Ω
.
When the exposed metal has no return path to the 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 1.5mA
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.
