China LT-20AMF LCD Schematic

COLOR TFT-LCD TV
SERVICE MANUAL

MODEL : LT-20AMF

CAUTION !!

BEFORE SERVICING THE TFT-LCD TV,
READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

LT-20AMF SERVICE MANUAL

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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 Replacement Parts List.
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.

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 of 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

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SERVICING PRECAUTIONS

CAUTION!!

Before servicing receivers covered by this service manual, read and follow the SAFETY
PRECAUTIONS on page 3 of this publication.

General Servicing Precautions

1.Always unplug the receiver AC power cord from AC power source before;

ⓐRemoving or reinstalling any component, circuit board module or any other receiver assembly.
ⓑDisconnecting or reconnecting any receiver electrical plug or other electrical connection.
ⓒ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 harzard.

2.Do not spray chemicals on or near this receiver or any of its assemblies.

3.Do not defect any plug/socket voltage interlocks with which receivers covered by this service
manual might be equipped.

4.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.

5.Do not connect the test fixture ground strap to power supply heatsink 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) Device.Examples

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 th separate from or “lift-off” the board.
The following guidelines and procedures should be flollowed 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 coopper pattern.

3.Bend a small “U” in one end of a small guage jumper wire and carefully crimp it around the IC
pin.

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.

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CONTENTS

Safety precautions ----------------------------------------------------------- 2

Servicing precautions ------------------------------------------------------- 3

Contents ------------------------------------------------------------------------- 4

Specifications ----------------------------------------------------------------- 5

Location of control ---------------------------------------------------------- 8

External in / output ---------------------------------------------------------- 11

Disassembly procedure ---------------------------------------------------- 12

Mechanical exploded view ----------------------------------------------- 20

Circuit descriptions --------------------------------------------------------- 21

Trouble shooting ------------------------------------------------------------- 35

Adjustment instruction with SVC mode ------------------------------ 38

Inspection instruction ------------------------------------------------------ 39

PCB Layout --------------------------------------------------------------------- 40

Part appearance -------------------------------------------------------------- 45

Packing instruction ---------------------------------------------------------- 47

Replacement Parts List ---------------------------------------------------- 48

Block diagram ---------------------------------------------------------------- 54

Connection diagram -------------------------------------------------------- 55

Schemetic diagram --------------------------------------------------------- 56

LT-20AMF SERVICE MANUAL

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SPECIFICATIONS

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

1.Scope.

This document is the specification of 20.1” TFT-LCD Color TV.

2.Power

1) Power requirement
DC 15V / 4.5A

2)AC / DC Adapter.

Input Frequency : 50/60㎐ ±3㎐
Input Voltage : AC 100V ～ AC 230V (±10%)

Output Voltage : DC 15V

3)Power cord
Use UL listed and CSA certified detachable power cord type ;SVT, 3-conductors, 18AWG
For AC 120V area. Use VDE listed detachable power cord type ;HO5VV-F, 3-conductors,

18AWG for AC 220～240V area.

3.Tuning system

FVS 100

4.Sound output

3W+3Wrms Stereo (Max)

5.Antenna input impedance

VHF / UHF at 75ohm

6.OSD Type (On Screen Display)

Windows type (Center)

7.External in/output

DC Power in, PC/DTV in, COMPONENT, Head Phone out, S-Video in, A/V input,A/V output,
ANT in.

Audio In : 0.4Vrms, over 10KΩ
Video In : 1Vp-p, over 75Ω
PC/DTV In: 0.7Vp, over 75Ω

8.Function

CATV/Hyper band
Auto Program
Manual Program
Auto Sleep
Quick view
PSM(Picture Status memory)
SSM(Sound Status memory)

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9.Receiving RF TV system

NO

Model System
1 PAL-B
2 PAL-G
3 PAL-I, I /I
4 PAL-D
5 PAL-K
6 SECAM-B
7 SECAM-G
8 SECAM-D
9 SECAM-K

10 SECAM-K1
11 SECAM-I (6.0)
12 NTSC-3.58 / 4.5
13 NTSC-3.58 / 5.5
14 NTSC-3.58 / 6.0
15 NTSC-3.58 / 6.5
16 NTSC-3.58 / 4.5(5.0)
17 NTSC-4.43 / 5.5
18 NTSC-4.43 / 6.0
19 NTSC-4.43 / 6.5
20 PAL 5.5 / 60Hz
21 PAL 6.0 / 60Hz
22 PAL 6.5 / 60Hz
23 SECAM 5.5 / 60Hz
24 SECAM 6.0 / 60Hz
25 SECAM 6.5 / 60Hz
26 SECAM L / L'

TOTAL SYSTEM 8

SPECIFICATIONS

LT-20AMF / /

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SPECIFICATIONS

10. PC Mode Scan Frequency & Timing

1)Scan Freq : H: 31 ～ 56 kHz / V : 56 ～ 75㎐

2)Preset Timing Chart

Mode Resolution H-Freq(Khz) V-Freq(Khz)

640x480

VGA

SVGA

DTV

640x480
640x480
720x400
800x600
800x600
800x600
800x600

1080i

720p
576p
480p

Note!! :

ⓐ If the set is cold, there may be a small “flicker” when the set is switched on. This is

Normal, there is nothing wrong with the set.

ⓑ if possible, use the VESA 640x480 PC video mode to obtain the best image quality for

your LCD TV. If used under the other resolutions, some scaled or processed pictures may
appear on the screen.

ⓒ some dot defects may appear on the screen, like Red, Green or Blue spot. However, this

will have no impact or effect on the monitor performance.

11. TFT – LCD Panel Character

1) Feature

Size :20.1" Diagonal
LCD Type :Color Active Matrix TFT
Pixel Pitch :0.2125mm(H) x 0.6375mm(V)
Pixel Format :640x480 Pixels, RGB Stripe
Active Video Area :408mm(H) x 306mm(V)
Surface treatment :Anti-reflective + Anti-glare coating.
Response Time(Typ) :16mS(Typ)
Viewing Angle<CR≥10> : Hor [Left/Right] Æ 80Deg (Typ) / 80Deg (Typ),

Ver [High(Top)/Low(Bottom)] Æ 70Deg (Typ) / 70Deg (Typ)

Luminance(Typ) : 450 cd/㎡(Typ)

Contrast Ratio(Typ) : 500:1 (Typ)
Display Color : 16,7M Color
Back Light : 6 CCFL

31KHZ

37.9KHz

37.5KHz

31.5KHz

35.1KHz

37.9KHz

48.1KHz

46.9KHz

60Hz
72Hz
75Hz
70Hz
56Hz
60Hz
72Hz

75Hz
50/60Hz
50/60Hz

50Hz

60Hz

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LOCATION OF CONTROL

A

All the function can be controlled with the remote controller.
Some functions can also adjusted with the buttons on the controls on the TV front panel.

12-1. Remote controller
Note !! : Before you use the remote controller, please install the batteries.

1.POWER:

Turns the TV on from standby or off to
standby mode.

2.MUTE:

Turns the sound on and off

3.NUMBER buttons:

Select channel numbers.

4.PSM (Picture Status Memory):

Recalls your preferred picture setting.

5.SSM (Sound Status Memory):

Recalls your preferred sound setting.

6.MENU:

Displays a main menu.

7. ST / SAP:

Selects the MTS-Stereo, Mono and
SAP

8.Q.VIEW:

Returns to the previously viewed
Programme.

9.TV / AV: Selects TV, COMPONENT,

VIDEO, S-VIDEO, RADIO(Only when
the set is Radio On.) or PC mode.
/ Clears the menu from the screen.

10.CH ▲▼ ( Channel Up/Down):

Selects next channel or a menu item.

11.OK:

ccepts your selection or displays the

current mode.

12.VOL ◀▶ ( Volume Up/Down):

Adjusts the sound level or a menu
Setting.

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LOCATION OF CONTROL

12-2. Remote controller
Note !! : Before you use the remote controller, please install the batteries.

13.CC

Sets the caption function.

14.MEMORY

Stores or removes the current
channel.

15.SLEEP

Sets the sleep timer.

16.PC/*

Selects PC mode directly.

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13. Controller of Panel
1 2 3 4 5 6 7

1. MENU

Display a menu.

2.

+ CH - (Channel Up/Down)

Selects a channel or a menu item

3. POWER INDICATOR

Illuminates red when the TV is in­power standby mode.
Illuminates green when the TV is­switched power on mode.
Illuminates amber when the PC mode is switched
power saving mode.

4. ON/OFF

Switches TV set on or off.

5. REMOTE CONTROL SENSOR

Accepts the IR signal of remote
controller.

+ VOL -( Volume Up/Down)

6.

Adjusts the volume.
Adjusts menu settings.

7. TV/AV

Selects input signal source.

Clears the menu from the screen.

LOCATION OF CONTROL

< FRONT VIEW >

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EXTERNAL IN / OUTPUT

14. EXTERNAL IN / OUTPUT

22 7

1) DC 15V IN

2) PC/DTV INPUT

3) COMPONENT IN

4) H/P(Headphone out)

Connect a headphone to this socket.

5) S-VIDEO IN

Connect the output of an S-VIDEO VCR to the S-VIDEO input.
Connect the audio outputs of an S-VIDEO VCR to the AV-IN audio inputs.

6) AV-IN

Connect the Audio/Video outputs of external equipment to these inputs.

7) AV-OUT

Connect the Audio outputs(L, R) of the set to Audio-IN(L, R) of another displayer or
the amplifier and the Video output of the set to Video IN of another displayer.

8) Ant. (Antenna input)

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DISASSEMBLY PROCEDURE

15. Deassembly procedure

1).Removal of Stand

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DISASSEMBLY PROCEDURE

2).Removal of Backcover

3).Removal of metal plate

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DISASSEMBLY PROCEDURE

4).Removal of metal chassis

5).Removal of Main PCB

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DISASSEMBLY PROCEDURE

6). Removal of connectors on Main PCB

7). Removal of inverter PCB

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DISASSEMBLY PROCEDURE

8). Removal of LCD Panel chassis

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