LG 22MB35DI Service Manual - 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 re-connecting 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.

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) is opropyl 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 easily

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

damage 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.

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.

Only for training and service purposes

SERVICING PRECAUTIONS

- 4 -

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 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

electrically 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 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 brushing 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 maintain tip temperature within the

range or 500ºF to 600ºF.

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 1.25cm) 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.

(500ºF to 600ºF)

b. Heat the component lead until the solder melts.

c. Quickly draw the melted solder with an anti-static, suction-

type solder removal device or with solder braid.

CAUTION: Work quickly to avoid overheating the circuit

board printed foil.

6. Use the following soldering technique.

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

(500ºF to 600ºF)

b. First, hold the soldering iron tip and solder the strand against

the component lead until the solder melts.

c. Quickly move the soldering iron tip to the junction of the

component lead and the printed circuit foil, and hold it there

only until the solder flows onto and around both the

component lead and the foil.

CAUTION: Work quickly to avoid overheating the circuit

board printed foil.

d. Closely inspect the solder area and remove any excess or

splashed solder with a small wire-bristle brush.

LGE Internal Use Only