LG M2550D User Manual Download

Page: 4 / 31

LGE Internal Use Only

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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.

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.

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.)

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.