LG RE-21FB50RX Service Manual Download Page 4

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CAUTION:

Before servicing receivers covered by this service

manual and its supplements and addenda, read and follow the

SAFETY PRECAUTIONS

on page 3 of this publication.

NOTE:

If unforeseen circumstances create conflict between the

following servicing precautions and any of the safety
precautions on page 3 of this publication, always follow the
safety precautions. Remember: Safety First.

General Servicing Precautions

1. Always unplug the receiver AC power cord from the AC

power source before;
a. Removing or reinstalling any component, circuit board

module or any other receiver assembly.

b. Disconnecting or reconnecting any receiver electrical plug

or other electrical connection.

c. Connecting a test substitute in parallel with an electrolytic

capacitor in the receiver.

CAUTION:

A wrong part substitution or incorrect

polarity installation of electrolytic capacitors may result
in an explosion hazard.

d. Discharging the picture tube anode.

2. Test high voltage only by measuring it with an appropriate

high voltage meter or other voltage measuring device (DVM,
FETVOM, etc) equipped with a suitable high voltage probe.
Do not test high voltage by "drawing an arc".

3. Discharge the picture tube anode only by (a) first connecting

one end of an insulated clip lead to the degaussing or kine
aquadag grounding system shield at the point where the
picture tube socket ground lead is connected, and then (b)
touch the other end of the insulated clip lead to the picture
tube anode button, using an insulating handle to avoid
personal contact with high voltage.

4. Do not spray chemicals on or near this receiver or any of its

assemblies.

5. Unless specified otherwise in this service manual, clean

electrical contacts only by applying the following mixture to
the contacts with a pipe cleaner, cotton-tipped stick or
comparable nonabrasive applicator; 10% (by volume)
Acetone and 90% (by volume) isopropyl alcohol (90%-99%
strength)

CAUTION:

This is a flammable mixture.

Unless specified otherwise in this service manual, lubrication
of contacts in not required.

6. Do not defeat any plug/socket B+ voltage interlocks with

which receivers covered by this service manual might be
equipped.

7. Do not apply AC power to this instrument and/or any of its

electrical assemblies unless all solid-state device heat sinks
are correctly installed.

8. Always connect the test receiver ground lead to the

receiver chassis ground before connecting the test receiver
positive lead.
Always remove the test receiver ground lead last.

Use with this receiver only the test fixtures specified in this
service manual.

CAUTION:

Do not connect the test fixture ground strap to

any heatsink in this receiver.

Electrostatically Sensitive (ES) Devices

Some semiconductor (solid state) devices can be damaged
easily by static electricity. Such components commonly are
called

Electrostatically Sensitive (ES) Devices.

Examples of

typical ES devices are integrated circuits and some fieldeffect

transistors and semicounductor "chip" components. The
following techniques should be used to help reduce the
incidence of component damage caused by static by static
electricity.
1. Immediately before handling any semiconductor component

or semiconductor-equipped assembly, drain off any
electostatic charge on your body by touching a known earth
ground. Alternatively, obtain and wear a commercially
available discharging wrist strap device, which should be
removed to prevent potential shock reasons prior to
applying power to the unit under test.

2. After removing an electrical assembly equipped with ES

devices, place the assembly on a conductive surface such as
aluminum foil, to prevent electrostatic charge buildup or
exposure of the assembly.

3. Use only a grounded-tip soldering iron to solder or unsolder

ES devices.

4. Use only an anti-static type solder removal device. Some

solder removal devices not classified as "anti-static" can
generate electrical charges sufficent to demage ES devices.

5. Do not use freon-propelled chemicals. These can generate

electrical charges sufficient to damage ES devices.

6. Do not remove a repalcement ES device from its protective

package until immediately before you are ready to install it.
(Most replacement ES devices are packaged with leads
electrically shorted together by conductive foam, aluminum
foil or comparable conductive material).

7. Immediately before removing the protective material from

the ieads of a replacement ES device, touch the protective
material to the chassis or circuit assembly into which the
device will be installed.

CAUTION:

Be sure no power is applied to the chassis or

circuit, and observe all other safety precautions.

8. Minimize bodily motions when handling unpackaged

replacement ES devices. (Otherwise harmless motion such
as the bruching together of your clothes fabric or the lifting
of your foot from a carpeted floor can generate static
electricity sufficient to damage an ES device.)

General Soldering Guidelines

1. Use a grounded-tip, low-wattage soldering iron and

appropriate tip size and shape that will maintan tip
temperature within the range or 500

¡£

F to 600

¡£

2. Use an appropriate gauge of RMA resin-core solder

composed of 60 parts tin/40 parts lead.

3. Keep the soldering iron tip clean and well tinned.
4. Thorohly clean the surfaces to be soldered. Use a mall

wirebristle (0.5 inch, or 1.25cm) brush with a metal handle.
Do not use freon-propelled spray-on cleaners.

5. Use the following unsoldering technique

a. Allow the soldering iron tip to reach normal temperature.