LG 20EN33T Servicehandleiding - Pagina 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 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.

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.

Only for training and service purposes

SERVICING PRECAUTIONS

- 4 -

9. 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.

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.)

LGE Internal Use Only