LG 37LC50CB, 37LC50CB-UA Schematic

		Internal Use Only
North/Latin America	http://aic.lgservice.com
Europe/Africa	http://eic.lgservice.com
Asia/Oceania	http://biz.lgservice.com

LCD TV

SERVICE MANUAL

CHASSIS : LA64A

MODEL : 37LC50CB 37LC50CB-UA

CAUTION

BEFORE SERVICING THE CHASSIS,

READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

CONTENTS

CONTENTS ..............................................................................................	2
PRODUCT SAFETY ..................................................................................	3
SPECIFICATION ........................................................................................	6
ADJUSTMENT INSTRUCTION ...............................................................	12
TROUBLE SHOOTING ............................................................................	18
BLOCK DIAGRAM...................................................................................	24
EXPLODED VIEW ..................................................................................	25
REPLACEMENT PARTS LIST ...............................................................	27
SVC. SHEET ...............................................................................................

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 2 -	LGE Internal Use Only
Only for training and service purposes

SAFETY PRECAUTIONS

IMPORTANT SAFETY NOTICE

Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts are identified by 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 it's 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 1W), keep the resistor 10mm 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 Check(Antenna 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 ohm-meter 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 1MΩ and 5.2MΩ.

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 1.5K/10watt resistor in parallel with a 0.15uF 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 ohms/volt 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 0.75 volt RMS which is corresponds to 0.5mA.

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 Volt-meter

	Good Earth Ground
	such as WATER PIPE,
To Instrument's	CONDUIT etc.
	0.15uF
exposed
METALLIC PARTS
	1.5 Kohm/10W

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 3 -	LGE Internal Use Only
Only for training and service purposes

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 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.

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.

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 wirebristle (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, suctiontype solder removal device or with solder braid.

CAUTION: Work quickly to avoid overheating the circuitboard 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.

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 4 -	LGE Internal Use Only
Only for training and service purposes

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.

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 anti-static suction-type 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 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 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 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

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.

Diode Removal/Replacement

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

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.

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.

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).

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.

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.

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.

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 5 -	LGE Internal Use Only
Only for training and service purposes

SPECIFICATION

NOTE : Specifications and others are subject to change without notice for improvement.

1.	Application range	3. Test method
	This specification is applied to LA64A chassis.
2.	Requirement for Test	3.1	Performance : LGE TV test method followed
		3.2	Demanded other specification
	Testing for standard of each part must be followed in below	Safety		: UL, CSA, IEC Specification
	condition.	EMC		: FCC, ICES, IEC

(1) Temperature : 20 ± 5°C

(2) Humidity : 65% ± 10%

(3) Power : 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.

(5) The receiver must be operated for about 20 minutes prior to the adjustment.

4. General Specification(TV)

No	Item		Specification	Remark
1	Receiving System	VSB/64 & 256 QAM/ NTSC-M
2	Available Channel	1)	VHF : 02~13
		2)	UHF : 14~69
		3)	DTV : 02-69
		4)	CATV : 01~135
		5) CADTV : 01~135
3	Input Voltage	1)	AC 100 ~ 240V 50/60Hz
4	Market	NORTH AMERICA
5	Screen Size	37, 42 inch Wide
6	Aspect Ratio	16:9
7	Tuning System	FS
8	LCD Module	LC370WX3-SLD1		LG Philips LCD
		LC420WX6-SLD1
9	Operating Environment	1)	Temp : 0 ~ 40 deg
		2)	Humidity : ~ 80 %
10	Storage Environment	1)	Temp. : -20 ~ 50 deg
		2)	Humidity : 10 ~ 90 %

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 6 -	LGE Internal Use Only
Only for training and service purposes

5. Chroma & Brightness

No	Item			Min	Typ	Max	Unit	Remark
1	White brightness			400	500		cd/m2	EZ Picture: Daylight, Color
								Temperature: Medium
2	Color coordinate	RED	X	0.602	0.632	0.662		Full Signal Swing
	(Default)		Y	0.312	0.342	0.372		± 0.025
		GREEN	X	0.258	0.288	0.318
			Y	0.580	0.610	0.640
		BLUE	X	0.117	0.147	0.177
			Y	0.035	0.065	0.095
		WHITE	X	0.246	0.287	0.296
			Y	0.254	0.289	0.304
3	Brightness uniformity			80			%	Full white
4	Contrast ratio			600:1	800:1			EZ Picture: Daylight, Color
								Temperature: Medium
5	Color Temperature	Standard		8,300	9,300	10,300	oK
		Cool		10,000	11,000	12,000	oK
		Warm		5,500	6,500	7,500	oK

6. Component Video Input (Y, CB/PB, CR/PR)

No	Resolution	H-freq(kHz)	V-freq.(kHz)	Proposed
1	720*480	15.73	59.94	SDTV ,DVD 480I
2	720*480	15.73	60.00	SDTV ,DVD 480I
3	720*480	31.47	59.94	SDTV 480P
4	720*480	31.50	60.00	SDTV 480P
5	1280*720	44.96	59.94	HDTV 720P
6	1280*720	45.00	60.00	HDTV 720P
7	1920*1080	33.72	59.94	HDTV 1080I
8	1920*1080	33.75	60.00	HDTV 1080I

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 7 -	LGE Internal Use Only
Only for training and service purposes

7. RGB Input (PC/DTV)

No	Resolution		H-freq(kHz)	V-freq.(Hz)	Pixel clock(MHz)	Proposed
	PC						DDC
1	640*350		31.469	70.08	25.17	DOS	X
2	640*480		31.469	59.94	25.17	VESA(VGA)	O
3	640*480		37.861	72.80	31.50	VESA(VGA)	O
4	640*480		37.500	75.00	31.50	VESA(VGA)	O
5	800*600		35.156	56.25	36.00	VESA(SVGA)	O
6	800*600		37.879	60.31	40.00	VESA(SVGA)	O
7	800*600		48.077	72.18	50.00	VESA(SVGA)	O
8	800*600		46.875	75.00	49.50	VESA(SVGA)	O
9	1024*768		48.363	60.00	65.00	VESA(XGA)	O
10	1024*768		56.476	70.06	75.00	VESA(XGA)	O
11	1024*768		60.023	75.02	78.75	VESA(XGA)	O
12	1280*768		47.700	60.000	80.140	VESA(WXGA)
	1360*768		47.720	59.799	84.750	VESA(WXGA)
	1366*768		47.130	59.658	72.000	VESA(WXGA)
	DTV
1	720*480		31.50	59.94		SDTV 480P
2	720*480		31.47	60.00		SDTV 480P
3	1280*720		44.96	59.94		HDTV 720P
4	1280*720		45.00	60.00		HDTV 720P
5	1920*1080		33.72	59.94		HDTV 1080I
6	1920*1080		33.75	60.00		HDTV 1080I
8. HDMI1 Input (PC/DTV)
No	Resolution		H-freq(kHz)	V-freq.(Hz)	Pixel clock(MHz)	Proposed
	PC						DDC
1	640*480		31.469	59.94	25.17	VESA(VGA)	O
2	640*480		37.861	72.80	31.50	VESA(VGA)	O
3	640*480		37.500	75.00	31.50	VESA(VGA)	O
4	800*600		35.156	56.25	36.00	VESA(SVGA)	O
5	800*600		37.879	60.31	40.00	VESA(SVGA)	O
6	800*600		48.077	72.18	50.00	VESA(SVGA)	O
7	800*600		46.875	75.00	49.50	VESA(SVGA)	O
8	1024*768		48.363	60.00	65.00	VESA(XGA)	O
9	1024*768		56.476	70.06	75.00	VESA(XGA)	O
10	1024*768		60.023	75.02	78.75	VESA(XGA)	O
11	1280*768		47.700	60.00	80.140	VESA(WXGA)	O
12	1360*768		47.720	59.799	84.750	VESA(WXGA)	O
13	1366*768		47.130	59.658	72.000	VESA(WXGA)	O
	DTV
1	720*480		31.500	59.94	27.00	SDTV 480P
2	720*480		31.469	60.00	27.03	SDTV 480P
3	1280*720		44.96	59.94		HDTV 720P
4	1280*720		45.00	60.00		HDTV 720P
5	1920*1080		33.72	59.94		HDTV 1080I
6	1920*1080		33.75	60.00		HDTV 1080I

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 8 -	LGE Internal Use Only
Only for training and service purposes

9. HDMI2 Input (DTV)

No	Resolution	H-freq(kHz)	V-freq.(Hz)	Pixel clock(MHz)	Proposed
1	720*480	31.500	59.94	27.00	SDTV 480P
2	720*480	31.469	60.00	27.03	SDTV 480P
3	1280*720	44.96	59.94		HDTV 720P
4	1280*720	45.00	60.00		HDTV 720P
5	1920*1080	33.72	59.94		HDTV 1080I
6	1920*1080	33.75	60.00		HDTV 1080I

10. General specifications (module)

10-1. 37LC5DC

No	Item		Value	Unit	Remark
1	Active Screen Size		940.3(diagonal)	mm	37.02 inches
2	Outline Dimension		877.0(H)x516.8(V)x46.9(D)	mm
3	Pixel Pitch		200 x 600 x RGB	um
4	Pixel Format		1366(H)x768(V) stripe arrangement
5	Color Depth		8bit 16.7	Mbit
6	Luminance ,White		500 (center 1 point typ)	cd/m2
7	Viewing Angle (CR>10)		R/L 178(Typ),U/D 178(Typ)	degree
8	Power Consumption		126	Watt
9	Weight		9	kg
10	Display Operating	Mode	Transmissive mode, normally black
11	Surface Treatment		Hard coating (3H)
10-2. 42LC5DC
No	Item		Value	Unit	Remark
1	Active Screen Size		1067.308 (diagonal)	mm	42.02 inches
2	Outline Dimension		983(H)x576(V)x47.3(D)	mm
3	Pixel Pitch		227 x 681 x RGB	um
4	Pixel Format		1366(H)x768(V) stripe arrangement
5	Color Depth		8bit 16.7	Mbit
6	Luminance ,White		450 (center 1 point typ)	cd/m2
7	Viewing Angle (CR>10)		R/L 178(Typ),U/D 178(Typ)	degree
8	Power Consumption		168.36	Watt
9	Weight		110(Typ), 12(Max)	kg
10	Display Operating	Mode	Transmissive mode ,normally black
11	Surface Treatment		Hard coating (3H)

Copyright © 2008 LG Electronics. Inc. All right reserved.	- 9 -	LGE Internal Use Only
Only for training and service purposes