LG 37LT75 (CHASSIS:LD74A) Service Manual ▷ View online
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IC Remove/Replacement
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.
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.
melts.
2. Draw away the melted solder with an anti-static suction-type
solder removal device (or with solder braid) before removing the
IC.
IC.
Replacement
1. Carefully insert the replacement IC in the circuit board.
2. Carefully bend each IC lead against the circuit foil pad and
2. Carefully bend each IC lead against the circuit foil pad and
solder it.
3. Clean the soldered areas with a small wire-bristle brush.
(It is not necessary to reapply acrylic coating to the areas).
"Small-Signal" Discrete Transistor
Removal/Replacement
1. Remove the defective transistor by clipping its leads as close as
Removal/Replacement
1. Remove the defective transistor by clipping its leads as close as
possible to the component body.
2. Bend into a "U" shape the end of each of three leads remaining
on the circuit board.
3. Bend into a "U" shape the replacement transistor leads.
4. Connect the replacement transistor leads to the corresponding
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.
long nose pliers to insure metal to metal contact then solder
each connection.
Power Output, Transistor Device
Removal/Replacement
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
Removal/Replacement
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.
5. Solder each transistor lead, and clip off excess lead.
6. Replace heat sink.
Diode Removal/Replacement
1. Remove defective diode by clipping its leads as close as
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
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.
necessary, apply additional solder.
Fuse and Conventional Resistor
Removal/Replacement
1. Clip each fuse or resistor lead at top of the circuit board hollow
Removal/Replacement
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.
3. Solder the connections.
CAUTION: Maintain original spacing between the replaced
component and adjacent components and the circuit board to
prevent excessive component temperatures.
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 "lift-off" the board. The
following guidelines and procedures should be followed whenever
this condition is encountered.
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 "lift-off" the board. The
following guidelines and procedures should be followed whenever
this condition is encountered.
At IC Connections
To repair a defective copper pattern at IC connections use the
following procedure to install a jumper wire on the copper pattern
side of the circuit board. (Use this technique only on IC
connections).
following procedure to install a jumper wire on the copper pattern
side of the circuit board. (Use this technique only on IC
connections).
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 out-away 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.
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.
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.
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.
connected to the affected copper pattern.
3. Connect insulated 20-gauge 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.
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.
- 6 -
SPECIFICATION
NOTE : Specifications and others are subject to change without notice for improvement.
4. General Specification
No.
Item
Specification
Remark
1.
Display Screen Device
32/37/42" wide Color Display Module
2.
Aspect Ratio
16:9
3.
LCD Module
32/37/42" TFT WXGA LCD
Maker : LPL
4.
Operating Environment
Temp. : 0 ~ 40 deg
Humidity : 0 ~ 85 %
5.
Storage Environment
Temp. : -20 ~ 60 deg
Humidity : 0 ~ 85%
6.
Input Voltage
AC100 ~ 240V, 50/60Hz
7.
Power Consumption
Power on (Green)
(42")Total 168.36W (Typ.) (Logic=6.36W, Backlight=162W )
(37") Total 126Watt (Typ.) (Logic=6W, Backlight =120W )
(32")Total 114.32W (Typ.) (Logic=4.32(4.1)W, Backlight =110W )
St-By (Red) : 1.0 W
8.
Type Size
760.0 x 450.0 x 48.0
32"
877.0 x 516.8 x 55.5
37"
1006 x 610 x 56
42"
9.
Pixel Pitch
0.17025 x 0.51075
32"
0.200 x 0.600
37"
0.227 x 0.681
42"
10.
Back Light
18 EEFL
32"
20 EEFL
37"
20 CCFL
42"
11.
Display Colors
16.7M (16,777,216)
12.
Coating
3H, AG
1. Application range
This spec sheet is applied to the 42"/37" LCD TV used LD74A
chassis
chassis
2. Specification
Each part is tested as below without special appointment.
(1) Temperature : 25 ± 5°C(77 ± 9°F), CST : 40 ± 5°C
(2) Relative Humidity : 65% ± 10%
(3) Power Voltage : Standard input voltage (100-240V~,
(2) Relative Humidity : 65% ± 10%
(3) Power Voltage : Standard input voltage (100-240V~,
50/60Hz)
*Standard Voltage of each products is marked by models
(4) Specification and performance of each parts are followed
each drawing and specification by part number in
accordance with BOM.
accordance with BOM.
(5) The receiver must be operated for about 20 minutes prior
to the adjustment.
3. Test method
(1) Performance : LGE TV test method followed
(2) Demanded other specification
(2) Demanded other specification
Safety
: CE, IEC Specification
EMC
: CE, IEC
- 7 -
5. LCD Module
No
Item
Min
Typ
Max
Unit
Maker
1
Luminance
400
500
cd/m
2
50cm from the surface
(W/O PC mode)
-Full White Pattern
2
View angle (R/L, U/D)
178/178
degree
32", 37" 42"
3
Color Coordinate
White
X
Typ.
0.279/0.279/0.279
Typ.
Y
-0.03
0.292/0.292/0.292
+0.03
Red
X
0.635/0.636/0.635
Y
0.339/0.343/0.344
Green
X
0.282/0.284/0.286
Y
0.606/0.615/0.614
Blue
X
0.145/0.144/0.146
Y
0.064/0.063/0.061
Contrast ratio
600
800
32"
(W/O PC mode)
700
900
37"
800
1000
42"
5
Luminance Variation
1.3
6. Component Video Input (Y, P
B
, P
R
)
No
Resolution
H-freq(kHz)
V-freq.(Hz)
Pixel clock(MHz)
Proposed
1.
720*480
15.73
60.00
SDTV, DVD 480i
2.
720*480
15.63
59.94
SDTV, DVD 480i
3.
720*480
31.47
59.94
480p
4.
720*576
15.625
50.00
SDTV, DVD 625 Line
5.
720*576
31.25
50.00
HDTV 576p
6.
1280*720
45.00
50.00
HDTV 720p
7.
1280*720
44.96
59.94
HDTV 720p
8.
1920*1080
31.25
50.00
HDTV 1080i
9.
1920*1080
33.75
60.00
HDTV 1080i
10.
1920*1080
33.72
59.94
HDTV 1080i
- 8 -
7. RGB Input ( PC )
7-1. EDID Data (RGB-PC)
No
Resolution
H-freq(kHz)
V-freq.(Hz)
Pixel clock(MHz)
Proposed
Remarks
1.
720*400
31.468
70.08
28.321
2.
640*480
31.469
59.94
25.17
VESA
Input 848*480 60Hz, 852*480 60Hz
37.684
75.00
31.50
=> 640*480 60Hz Display
3.
800*600
37.879
60.31
40.00
VESA
46.875
75.00
49.50
4.
832*624
49.725
74.55
57.283
Macintosh
5.
1024*768
48.363
60.00
65.00
VESA(XGA)
56.470
70.00
75.00
60.123
75.029
78.75
6.
1280*768
47.78
59.87
79.5
WXGA
7.
1360*768
47.72
59.8
84.75
WXGA
8.
1366*768
47.56
59.6
84.75
WXGA
9.
1280*1024
63.595
60.0
108.875
SXGA
FHD Model only
10.
1400*1050
65.160
60.0
122.50
SXGA
FHD Model only
11.
1600*1200
74.077
60.0
130.375
UXGA
Reduced Blanking Timing, FHD Model only
Input 1920*1200 60Hz Ë 1600*1200 60Hz Display
12.
1920*1080
66.647
59.988
138.625
WUXGA
Reduced Blanking Timing
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