LG 28LJ400B Скачать руководство пользователя страница 4

Страница: 4 / 38

- 4 -

ⓒ

Only training and service purposes.

SERVICING PRECAUTIONS

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 precau-
tions. 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 explo-
sion hazard.

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

assemblies.

4. 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
non-abrasive 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.

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

receivers covered by this service manual might be equipped.

6. 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.

7. 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.

8. Use with this receiver only the test fixtures specified in this

service manual.

CAUTION: Do not connect the test fixture ground strap to any
heat sink in this receiver.

Electrostatically Sensitive (ES) Devices

Some semiconductor (solid-state) devices can be damaged eas-
ily by static electricity. Such components commonly are called
Electrostatically Sensitive (ES) Devices. Examples of typical ES
devices are integrated circuits and some field-effect transistors
and semiconductor “chip” components. The following techniques
should be used to help reduce the incidence of component dam-
age caused by static by static electricity.

1. Immediately before handling any semiconductor component or

semiconductor-equipped assembly, drain off any electrostatic
charge on your body by touching a known earth ground. Alter-
natively, obtain and wear a commercially available discharg-
ing 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 expo-
sure 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 sol-

der removal devices not classified as “anti-static” can generate
electrical charges sufficient to damage ES devices.

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

electrical charges sufficient to damage ES devices.

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

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

7. Immediately before removing the protective material from the

leads of a replacement ES device, touch the protective mate-
rial to the chassis or circuit assembly into which the device will
be installed.

CAUTION: Be sure no power is applied to the chassis or cir-
cuit, and observe all other safety precautions.

8. Minimize bodily motions when handling unpackaged replace-

ment ES devices. (Otherwise harmless motion such as the
brushing together of your clothes fabric or the lifting of your
foot from a carpeted floor can generate static electricity suf-
ficient to damage an ES device.)

General Soldering Guidelines

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

ate tip size and shape that will maintain tip temperature within
the range or 500 °F to 600 °F.

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. Thoroughly clean the surfaces to be soldered. Use a mall wire-

bristle (0.5 inch, or 1.25 cm) 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.

(500 °F to 600 °F)