LG 55LB6500 User manual

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LED TV
SERVICE
MANUAL
CHASSIS LA42B
MODEL
55L
6500
CAUTION
BEFORE SERVICING THE
CHASSIS
READ THE SAFETY PRECAUTIONS IN THIS MANUAL
PNO
MFL6804520211401RFV00
Confidential Business Information
Subject
to Protective
Order
Printed in
Korea
LGE910IT000143504
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CONTENTS
CONTENTS
2
PRODUCT SAFETY
3
SPECIFICATION 4
ADJUSTMENT
INSTRUCTION 13
EXPLODED VIEW 24
SCHEMATIC CIRCUIT DIAGRAM
Copyright
n 2014
LG
Electronics Inc All
rights reserved
2
Only
for
training
and service
purposes
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SAFETY PRECAUTIONS
IMPORTANT SAFETY NOTICE
Many
electrical and mechanical
parts
in this chassis have
special safetyrelated
characteristics These
parts are
identified
by
b in the
Schematic Diagram and
Exploded
View
It is essential that these special safety parts should be
replaced with the
same
components
as recommended in this manual to
prevent
Shock Fire or
other Hazards
Do not modify the
original design without permission
of manufacturer
General Guidance
An isolation Transformer should always be used
during the
servicing
of a receiver whose chassis is not isolated from the AC
power
line Use a transformer of
adequate power rating
as this
protects the technician from accidents resulting
in
personal injury
from electrical shocks
It will also protect the receiver and its
components
from
being
damaged by
accidental shorts of the
circuitry
that
may
be
inadvertently introduced during the service operation
If
any
fuse
or
Fusible
Resistor
in this TV receiver is blown
replace
it with the specified
When
replacing
a
high wattage
resistor
Oxide
Metal Film
Resistor
over 1
W keep
the resistor 10 mm
away
from PCB
Keep
wires
away
from high voltage or
high temperature parts
Before
returning the receiver to the customer
always perform
an AC
leakage
current check on the
exposed
metallic
parts
of the cabinet such
as antennas terminals etc
to
be
sure the set
is safe
to
operate
without
damage
of electrical
shock
Leakage
Current Cold
CheckAntenna
Cold
Check
With the instrument AC
plug
removed from AC
source connect
an
electrical
jumper across
the two AC
plug
prongs Place
the AC
switch in the
on
position
connect
one
lead of ohm meter to the AC
plug prongs
tied
together
and touch other ohmmeter lead in turn to
each exposed metallic
parts
such
as antenna terminals
phone
jacks
etc
If the
exposed
metallic part has a return
path
to the
chassis
the
measured resistance should be between 1 MO and 52 MO
When the
exposed
metal has no return
path
to the chassis the
reading
must be infinite
An other
abnormality
exists that must be corrected before the
receiver is returned to the customer
Leakage
Current Hot Check
See
below
Figure
Plug the
AC cord
directly into
the AC outlet
Do not use a line Isolation Transformer
during
this check
Connect 15 K 10 watt resistor in
parallel
with a 015 uF
capacitor
between a known good earth
ground Water Pipe Conduit etc
and the
exposed
metallic
parts
Measure the AC
voltage
across
the resistor
using
AC voltmeter
with 1000 ohmsvolt
or more sensitivity
Reverse
plug the
AC cord into the AC outlet and
repeat
AC
voltage
measurements for each exposed metallic
part Any voltage
measured must not exceed 075 volt RMS which is
corresponds
to
05 mA
In case
any
measurement is out of the limits
specified there
is
possibility
of shock hazard and the set must be checked and
repaired before
it is returned to the customer
Leakage
Current Hot Check circuit
AC Voltmeter
To Instruments
exposed
METALLIC PARTS
Good Earth Grcund
such
as
WATER
PIPE
CONDUIT etc
When 25A is
impressed
between Earth and 2nd Ground
for
1 second Resistance must
be less than
01 0
xBase on
Adjustment standard
Copyright
n 2014 LG Electronics Inc All
rights
reserved
Only
for
training
and service
purposes
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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 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
einstallatioxn
of
elpectrolyticlcaopacitorssmay riesuolt
in
ann
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 cottontipped
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
5
Do
not defeat
any
plugsocket
B
voltage
interlocks with which
receivers covered by this service manual
might
be equipped
6 Do not apply AC
power
to this instrument andlor
any
of its
electrical assemblies unless all solidstate 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
solidstate
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 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
semiconductorequipped assembly
drain off
any
electrostatic
cAharge olntyouer bodyrbyntouchinag
a
ktnowinvearthegroundly
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
groundedtip soldering iron to solder or
unsolder
ES
devices
4 Use
only an
antistatic
type
solder removal device
Some
solder
removal devices not classified as antistatic can
generate
electrical
charges
sufficient to
damage
ES devices
5
Do
not use
freonpropelled 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
Meost relplaceementcES detvicesrareipacckagedawith leladsly
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
Mriniemize bpodily lmoations cwhenehandlinmg unpackaeged nt
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
groundedtip lowwattage soldering iron
and
appropriate
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 resincore solder composed
of 60
parts
tin40
parts
lead
3
Keep
the
soldering iron tip
clean and well tinned
4
Twhoroughly icleran thee surfacbes
to
bersoldieresd Useta mlalle
05 inch
or 125
cm
brush with a metal handle
Do
not use
freonpropelled sprayon cleaners
5 Use the
following unsoldering technique
a
Allow the
soldering iron tip
to reach normal temperature
500
F to 600
F
b Heat the
component
lead until the solder melts
csQuicklyudrawcthe mteltiedosoldernwith atn ayntistatipc e
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
500 F to 600 F
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 wirebristle brush
Copyright
n 2014
LG
Electronics Inc All
rights reserved
Only
for
training
and service
purposes
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IC
RemoveReplacement
Some
chassis circuit boards have slotted holes oblong
through
which the IC leads are inserted and then bent flat
against the
circuit
foil
When
holes are the slotted
type
the
following technique
should be used to
remove and
replace the
IC
When
working
with
boards using the familiar round hole use the standard technique
as
outlined in
paragraphs
5 and 6 above
Removal
1
Desolder and
straighten
each IC lead in one
operation by
gently prying up on
the lead with the
soldering iron tip
as the
solder melts
2
Draw away
the melted solder with
an
antistatic
suctiontype
solder removal device or with solder
braid
before
removing
the IC
Replacement
1
Carefully
insert the
replacement
IC in the circuit board
2
Carefully
bend each IC lead against the circuit foil
pad and
solder it
3 Clean the soldered
areas
with
a
small wirebristle brush
It
is not
necessary
to
reapply acrylic coating
to the
areas
SmallSignal
Discrete Transistor
RemovalReplacement
1 Remove the defective transistor
by clipping
its leads
as
close
as
possible to
the
component body
2 Bend into
aU
shape
the end of each of three leads
remaining
on
the circuit board
3 Bend into aU
shape
the
replacement
transistor leads
4 Connect the
replacement
transistor leads to the
corresponding
leads extending from the circuit board and
crimp
the
U
with
long
nose
pliers
to insure metal to metal contact then solder
each connection
Power
Output
Transistor Device
RemovalReplacement
1 Heat and remove all solder from around the transistor leads
2
Remove
the heat sink
mounting screw if
so equipped
3
Carefully
remove the transistor from the heat sink of the circuit
board
4 Insert new transistor in the circuit board
5 Solder each transistor
lead
and
clip off
excess lead
6
Replace
heat sink
Diode RemovalReplacement
1 Remove
defective diode
by clipping
its leads as close as
possible
to diode
body
2 Bend the two
remaining
leads perpendicular
y
to the circuit
board
3
Observing diode polarity
wrap each
lead of the
new
diode
around the
corresponding
lead on the circuit board
4
Securely crimp
each connection and solder it
5
Inspect on
the circuit board copper
side
the solder
joints
of
the two
original
leads If
they are not shiny
reheat them and if
necessary apply
additional solder
Fuse and Conventional Resistor
RemovalReplacement
1
Clip
each fuse or resistor lead at
top
of the circuit board hollow
stake
2
Securely crimp
the leads of
replacement
component around
notch at stake
top
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and service
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3 Solder the connections
CAUTION Maintain
original spacing
between the replaced
component and adjacent components and
the circuit board to
prevent excessive component temperatures
Circuit Board Foil
Repair
Excessive heat
applied
to the
copper
foil of
any
printed
circuit
board will
weaken
the adhesive that bonds the foil to the circuit
board
causing
the foil to
separate
from or liftoffthe board The
following guidelines
and
procedures should
be followed whenever
this condition is encountered
At
C
Connections
To
repair
a defective
copper
pattern at
IC connections use the
following procedure
to install a
jumper
wire on the
copper
pattern
scide ofothe cirncuit bonard Uese thics techntiqueioonly onnIC s
1
Carefully
remove
the
damaged
copper pattern with
a
sharp
knife
Remove only as
much
copper as
absolutely necessary
2
carefully
scratch
away
the solder resist and
acrylic coating if
used from the end of the
remaining
copper
pattern
3 Bend a small
U
in one end of a small
gauge
jumper
wire and
carefully crimp
it around the IC
pin
Solder the IC connection
4 Route the
jumper
wire
along
the path of the
outaway
copper
pattern
and let it
overlap the previously scraped end
of the
good copper pattern
Solder the
overlapped area
and
clip off
any excess
jumper wire
At Other Connections
Use the
following technique
to repair the defective
copper pattern
at connections other than IC Pins This
technique
involves the
installation of a
jumper
wire on the
component
side of the circuit
board
1
Remove
the defective
copper
pattern with
a
sharp
knife
Remove at least 1 4 inch of
copper
to ensure that a hazardous
condition will not exist if the
jumper
wire
opens
2 Trace
along
the
copper pattern
from both sides of the
pattern
break and locate the nearest
component
that is
directly
connected
to the affected
copper pattern
Connect insulated 20gauge
jumper
wire from the lead of the
nearest
component on one
side of the
pattern
break to the lead
of the nearest
component on
the other side
Carefully crimp
and solder the connections
CAUTION Be sure the insulated
jumper
wire is dressed so the
it does not touch components
or
sharp
edges
5
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