AOC Envision L20S421 User manual

20” LCD TV Color Monitor AOC L20S421
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Service
Service
Service
TABLEOFCONTENTS
Description Page Description Page
SAFETY NOTICE
ANY PERSON ATTEMPTING TO SERVICE THIS CHASSIS MUST FAMILIARIZE HIMSELF WITH THE
CHASSIS AND BE AWARE OF THE NECESSARY SAFETY PRECAUTIONS TO BE USED WHEN SERVICING
ELECTRONIC EQUIPMENT CONTAINING HIGH VOLTAGE
Table Of Contents.......……..............................…........1
Revision List.…........................................……......2
Important Safety Notice.……..................……......3
1.General Specifications..............................………........4
2.Operating Instructions………..…………………….......6
2.1.The Use of Remote Control…................……...........6
2.2.To Use the Menu………..............................…...........7
2.3.LCD TV Description…….…..............……...............14
2.4.Interface Connector……............................…...........14
3.Precautions and Notices…............……………............15
3.1.Assembly Precaution…............………….................15
3.2.Operating Precaution…………...........................15
3.3.Storage Precaution…......………………..................15
3.4.High Voltage Warning.…..........…………................15
4.Input/Output Description……..…………… ...........16
4.1.D-SUB Connector……...…………………....….......16
4.2.Factory Preset Display Modes……………..….......17
5.Front Panel Control Knobs…....................................18
6.Repair Flow Chart…….............................................19
7.Mechanical Instructions……………................25
8.Exploded View…………….......................................29
9.Parts List of Cabinet………………………….............30
10.PCB Layout..………….......................................58
10.1.Main Board……….....…….................................58
10.2.Power Board…...………...................................60
10.3.Tuner Board…………........................................63
10.4.IR Board……………….......................................66
10.5.Headphone Board………..................................67
10.6.Keypad Board…………......................................67
11.Block Diagram………………..............................68
12.Schematic Diagram………………...............…69
12.1.Main Board.............................................69
12.2.Power Board....……....................................82
12.3.Tuner Board....……....................................85
CAUTION: USE A SEPARATE ISOLATION TRANSFOMER FOR THIS UNIT WHEN SERVICING

20” LCD TV Color Monitor AOC L20S421
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Revision List
Revision Date Revision History TPV Model
A00 Jun-09-06 First Version Release EAA6CHNKD1ACTMP

20” LCD TV Color Monitor AOC L20S421
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Important Safety Notice
Proper service and repair is important to the safe, reliable operation of all AOC Company Equipment. The service
procedures recommended by AOC and described in this service manual are effective methods of performing service
operations. Some of these service operations require the use of tools specially designed for the purpose. The
special tools should be used when and as recommended.
It is important to note that this manual contains various CAUTIONS and NOTICES which should be carefully read in
order to minimize the risk of personal injury to service personnel. The possibility exists that improper service
methods may damage the equipment. It is also important to understand that these CAUTIONS and NOTICES ARE
NOT EXHAUSTIVE. AOC could not possibly know, evaluate and advise the service trade of all conceivable ways in
which service might be done or of the possible hazardous consequences of each way. Consequently, AOC has not
undertaken any such broad evaluation. Accordingly, a servicer who uses a service procedure or tool which is not
recommended by AOC must first satisfy himself thoroughly that neither his safety nor the safe operation of the
equipment will be jeopardized by the service method selected.
Hereafter throughout this manual, AOC Company will be referred to as AOC.
WARNING
Use of substitute replacement parts, which do not have the same, specified safety characteristics may create shock,
fire, or other hazards.
Under no circumstances should the original design be modified or altered without written permission from AOC.
AOC assumes no liability, express or implied, arising out of any unauthorized modification of design.
Servicer assumes all liability.
FOR PRODUCTS CONTAINING LASER:
DANGER-Invisible laser radiation when open AVOID DIRECT EXPOSURE TO BEAM.
CAUTION-Use of controls or adjustments or performance of procedures other than those specified herein may
result in hazardous radiation exposure.
CAUTION -The use of optical instruments with this product will increase eye hazard.
TO ENSURE THE CONTINUED RELIABILITY OF THIS PRODUCT, USE ONLY ORIGINAL MANUFACTURER'S
REPLACEMENT PARTS, WHICH ARE LISTED WITH THEIR PART NUMBERS IN THE PARTS LIST SECTION OF
THIS SERVICE MANUAL.
Take care during handling the LCD module with backlight unit
-Must mount the module using mounting holes arranged in four corners.
-Do not press on the panel, edge of the frame strongly or electric shock as this will result in damage to the screen.
-Do not scratch or press on the panel with any sharp objects, such as pencil or pen as this may result in damage to
the panel.
-Protect the module from the ESD as it may damage the electronic circuit (C-MOS).
-Make certain that treatment person’s body is grounded through wristband.
-Do not leave the module in high temperature and in areas of high humidity for a long time.
-Avoid contact with water as it may a short circuit within the module.
-If the surface of panel becomes dirty, please wipe it off with a soft material. (Cleaning with a dirty or rough cloth may
damage the panel.)

20” LCD TV Color Monitor AOC L20S421
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1. General Specifications
Function
20" Screen
Resolution (640x480)
High Brightness ( 350 cd/m2)
High Contrast Ratio (400:1)
Viewing angel (170° H/ 170° V )
Item Spec
Screen Size 20” TFT-LCD Panel
Aspect Ratio 4: 3
Resolution 640 x480 (VGA)
Display Area (opening) H x V 408mm x 306mm
Pixel Pitch 0.63mm x 0.63mm
Display Colors 16.7 million
Contrast Ratio 400:1
Brightness 350 cd/㎡
Viewing angel 170° H/ 170°V
Response Time 16ms
Lamp Type/Life 50000 hr
LCD Panel
Color Temperature Cool / Warm/Normal
Input support definition 640*480 /60Hz
VGA Function
Audio input Mini jack for stereo headphones (3.5ø)
TV Standard NTSC M
Sound System MTS、SAP
TV Function
Colour systems NTSC
AV RCA x 1
S-VIDEO S-Videox 1
Audio L/R x 1
Video Input
Component YPbPr x 1 Audio L/R x 1

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Speaker (built-in): Two 2 watt speakers
Audio output Audio output: L / R
Headphone Mini-jack for stereo (3.5ø)
OSD Language English. French. German. Spanish. Portuguese.
Traditional Chinese
Table Stand Yes
Wall Mount VESA 100 x 100 mm
Power AC100V-240V, 50/60Hz
Power
Power Consumption <70W
Panel Tilt Forwards/Backwards/
Rotation -4°/ +18° / ± 35°
Temperature + 0 °C ~ + 40 °C
storage - 25 °C ~ + 60 °C
Environment
operating 10% ~ 85%
Dimension W x H x D (with stand) 498 x 495 x 180 (mm)
Net weight Without accessory 9.7 Kg
Accessory Remote controller, Batteriesx2, Power cord, Signal Cable,
Audio Cable, User manual

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2. Operating Instructions
2.1. The Use Of Remote Control
Note 1,3: SWAP, POP function
2: SIZE functions (optio
POWER
Press to turn on/off the
TV. The TV is never
completely powered off
unless it is physically
unplugged.
0~9/100 Digit buttons
To select a TV channel.
CH
Press or (or ) to
browse through the TV
channels,which are not
erased. To view a blocked
channel, use the digital
buttons to access，the
channel and enter your
access code.
VOL
Press + or – to adjust the
volume.
PC
Press this button to turn
PC mode
SLEEP
With this key you can set a
time period after which the
TV should switch itself to
standby. Press the key
repeatedly to select the
number of minutes. The
counter runs from
5,10,15,20,25…120
minutes.
PIP
Not Supported.
POP
Not Supported.
MENU
Press repeatedly to display
OSD menu.
SIZE
Includes 3 modes. Press
repeatedly to select 4:3: to
16:9 (Linear) / 4:3 to 16:9
(non-Linear) /16:9 (option)
MUTE
Temporarily interrupt the
sound or restore it.
DISPLAY
Press this button to
Display Channel number
on the right-top corner.
MTS /SAP
Press this key to activate
Multichannel Television
Sound, Stereo or Mono
sound.
PRE-CH
To display the previously
selected TV channel.
TV/VIDEO
Select your input source:
press repeatedly to select
TV, AV, S-VIDEO, PC.
CAPTION
Press this button to turn
Closed Caption on.
Be sure you have
selected Caption On in
the Setup menu.
Up & Down
Press Up and Down
we Can select the sub menu
Left & Right
Press Left and Right, we can
Change the Setting of
submenu

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2.2 To Use The Menus
1. Press the MENU button repeatedly to display each menu
2. Use the cursor up/down to select a menu item or adjust the setting of Menu item.
3. Use the cursor left/right to enter a submenu or enable the function.
4. Press the MENU button to exit the menu.
Main Menu
Press the MENU button to enter the main OSD (On Screen Display). Adjust the items including Picture Setup,
Sound setup, Child Lock Setup, Function Setup and TV setup. When the input source is PC or Component mode,
only the Sound Setup, Picture Setup and Menu Setup can be selected; shown in the figure below:
When the input source is AV or S-Video mode, the Sound Setup, Picture Setup, Child Lock Setup and Function
Setup can be selected; shown in the figure below:
When the input source is TV mode, the Sound Setup, Picture Setup, Child Lock Setup, Function Setup and TV
Setup can be selected, shown in the figure below:

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Sound Setup (Same as in PC, TV, AV1, S-Video and Components modes)
1. The range of adjusting volume, bass and treble is from 0~100.
2. Select “ON” or “OFF” in sound selection to control the sound output.
3. The range of adjusting Balance is -50~+50; when adjusting from 0 to -50, the sound from the left track fades
until silence; when adjusting from 0 to +50, the sound from the right track fades until silence.
4. AVL: you can set it “ON” or “OFF”.
The function is to adjust the input sound automatically. You may enable this function when you notice that the
sound in the two tracks are very different, in order to prevent the bad sound effect resulting from large sound
variation.
5. Select "ON" or "OFF" for Loudness: a default setting is preset, and you may adjust when necessary.
The following menu will appear when selecting continuously:
6. Preset: Designed for different types of sound output, wherein, the dialogue, music and theater modes are preset;
you can set Bass, Treble and Equalizer in sound output mode according to your preference.
7. Equalizer: You can select and adjust 100, 300, 1K, 3K and 8K respectively (the figures represent the sound
frequency range).
8. Reset to default: Reset the sound setting to the factory default value.
Picture Setting
When the input source is in PC mode, you can select Brightness, Contrast, Position, Video noise, Sharpness, Auto
Adjust, Info, Color Temp, Red, Green, Blue and Reset to default; shown in the figure below:

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1. Brightness and Contrast: The range can be adjusted from 0~100.
2. Position: There are two options, Horizontal and Vertical, which can be adjusted from -50 to +50.
3. Video noise: There are two options, Phase and Clock, which can be adjusted from -50 to +50.
4. Sharpness: Select from five options of Softest, Soft, Auto, Sharp and Sharpest. You may adjust the above
options according to your preference.
5. Auto Adjust: Automatically adjust PC input to the optimal screeen size.
6. Info: Prompt the current size for PC input definition (only the definition that can be shown by this device).
7. Colour Temp.: There are four options of colour temperature provided for users - 6500, 7300, 9300 and
Personal. You can select the three colour temperatures of 6500, 7300 and 9300, or manually adjust red, green
or blue in the personal setting (you can only adjust red, green and blue in the personal setting).
8. Reset to default: It is used to reset the picture settings to the factory default mode.
When the input source is in TV/AV1/S-Video/ mode, you can select Brightness, Contrast, Colour, Sharpness, Tint,
Dyn. skin tone, Colour Temp., Public, Zoom and Reset to default respectively; shown in the figure below:

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When the input source is in Component mode, you can select Brightness, Contrast, Colour, Sharpness,
Tint,White tone, Size and Reset to default respectively; shown in the figure below:
1. Brightness and Contrast: The range can be adjusted from 0~100; use Brightness and Contrast options to adjust
the brightness of picture.
2. Colour: The range can be adjusted from 0~100; use this option to adjust the colour saturation of picture.
3. Sharpness: Select from five options of Softest, Soft, Auto, Sharp and Sharpest. You can adjust the sharpness of
picture using any option above.
4. Tint: The range can be adjusted from -50~+50; use this option to adjust the colour of picture.
5. Dyn. Skin tone: When the Dynamic skin tone is ON, the skin tone of person in the picture becomes more vivid.
6. Colour Temp.: There are three options of colour temperature provided for users - warm, normal and cool.
7. Size: There are various functions provided for zoom in/zoom out.
8. Reset: It is used to reset the picture settings to the factory default mode.
Function Setup
When the input source is in TV, AV1 or S-Video mode, you can select Source OSD, Language, Child lock, Timers,
CC Mode and Reset to default; shown in the figure below:

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1. Current Source OSD setting: When OSD is set to ON, the left upper corner of the display will show the input
source or the TV channel number; when OSD is set to OFF, the input source or the TV channel number will
disappear.
2. OSD language setting: There are six language options provided - English, French, German, Spanish,
Portuguese and Traditional Chinese.
3. Child Lock Setup;
(1). You can enter the V-Chip level setting only when the Child Lock is ON, and the V-Chip will be enabled; you
can not enter V-Chip level setting when the Child Lock Setup is OFF, and the V-Chip is disabled.
(2). Lock code: V-Chip password can be set up when the code is locked. Enter the 4-digit password which you
choose! The factory default password is 0000.
4. Sleep Timer: Set the sleeping timer and the alert function which indicates the time left.
5. Closed Caption (CC) setting: Select CC1~CC4, TXT1~TXT4 or OFF.
6. Reset: It is used to reset the OSD settings.
When the input source is in PC or Component mode, you can select Source OSD, Language, Timers and Reset to
default; shown in the figure below:

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Source OSD, Language, Timers and Reset to default options are operated similarly as the above instructions!
Child Lock
When the input source is in TV, AV1 or S-Video mode, V-Chip level can be set. You can enter the Child Lock setting
only when the Child Lock is ON. When you enter the Child Lock setting, a message on the display will prompt you to
enter password:
You can enter the Child Lock setting to set up the V-Chip level when you enter the correct password:
1. Age: it may be set to Child, Teenager, Youth, Adult, Custom or OFF; when you select Custom, it can be set
according to you preference.
2. MPAA Rating: Select the movie ratings from low to high (alert) - G, PG, PG-13, R, NC-17, X and F.
3. PG Rating: Shown in the figure below:
The empty box refers to unlocked; the solid box refers to locked.
4. Reset to default: Reset to the factory default value.

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TV Setting
The following menu appears only in the TV mode.
1. Channel nr: Shows the current channel number.
2. Tuning mode: Select the mode of TV signal - Cable\HRC Cable\IRC Cable\ Broadcast.
3. System standard: NTSC-M, Auto.
4. Auto search: Select "Auto Search" to search all signaled channel; when the searching is complete, it stays at the
first channel with signal and all channels that have been located are stored. If you would like to stop "Auto
Search" during the process, simply by pressing the function button.
5. Fine tune: NTSC-M is seldomly used.
6. AFC can be set to ON or OFF. When it is set to ON, the TV will search the TV signal automatically; when there is
any offset in the signal, it will automatically adjust the channel to the correct positon.
7. Skip can be set to ON or OFF. When it is set to ON, a channel can be skipped by pressing the switching button
on the remote control or on the front panel.
8. Reset to default: Reset to the factory default value.

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2.3 LCD TV Description
The LCD TV will contain a main board, a power board, an IR board, a function keyboard, a tuner board and a
headphone Board. The main board and power board will house the flat panel to control logic I²C bus, DDC,
brightness control logic for LCD panel, DC-DC conversion to supply the appropriate power to the whole board
and transmitting TTL level signals into LCD Module to drive the LCD display circuit.
The inverter board will drive the six CCFLs (Cold Cathode Fluorescent Tube).
The switching power board will provides the power ON/OFF to control the TV and control LED indicator for
DPMS.
The function keyboard and Remote Control will provide the OSD control signal to the Main Board.
2.4 Interface Connector
(A) Power Cord Connector.
(B) RF Signal Connector.
(C) Video / Audio Signal Connectors.
(D) PC D-sub 15 pin Connector.
(E) PC Audio Connector
(F) AV Connector
(G) S-Video Connector
(H) Component Connector

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3. Precautions and Notices
3.1 Assembly Precaution
(1) Please do not press or scratch LCD panel surface with anything hard. And do not soil LCD panel surface
by touching with bare hands (Polarize film, surface of LCD panel is easy to be flawed)
In the LCD panel, the gap between two glass plates is kept perfectly even to maintain display
characteristic and reliability. If this panel is subject to hard pressing, the following occurs:
(a) Uniform color (b) Orientation of liquid crystal becomes disorder
(2) Please wipe out LCD panel surface with absorbent cotton or soft cloth in case of it being soiled.
(3) Please wipe out drops of adhesive like saliva and water in LCD panel surface immediately.
They might damage to cause panel surface variation and color change.
(4) Do not apply any strong mechanical shock to the LCD panel.
3.2 Operating Precaution
(1) Please be sure to unplug the power cord before remove the back-cover. (Be sure the power button is
turn-off)
(2) Please do not change variable resistance settings in MAIN-BOARD; they are adjusted to the most
suitable value. If they are changed, it might happen LUMINANCE does not satisfy the white balance
spec.
(3) Please consider that LCD backlight takes longer time to become stable of radiation characteristic in low
temperature than in room temperature.
(4) Please pay attention to displaying the same pattern for very long-time. Image might stick on LCD.
3.3 Storage Precaution
(1) When you store LCD for a long time, it is recommended to keep the temperature between -10°C -50°C
without the exposure of sunlight and to keep the humidity less than 85% RH.
(2) Please do not leave the LCD in the environment of high humidity and high temperature such as 60°C,
85%RH.
(3) Please do not leave the LCD in the environment of low temperature: below -10°C.
3.4 High Voltage Warning
The high voltage was only generated by INVERTER module on Power Board, if carelessly contacted the
transformer on this module, can cause a serious shock. (The lamp voltage after stable around 600V, with
lamp current around 8mA, and the lamp starting voltage was around 1500V, at Ta=25°C)

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4. Input/Output Description
4.1 D-SUB Connector
This procedure gives you instructions for installing and using the LCD TV display.
1. Position the display on the desired operation and plug the power cord into a convenient AC outlet.
Three-wire power cord must be shielded and is provided as a safety precaution as it connects the chassis
and cabinet to the electrical conduct ground. If the AC outlet in your location does not have provisions for
the grounded type plug, the installer should attach the proper adapter to ensure a safe ground potential.
2. Connect the 15-pin color display shielded signal cable to your signal system device and lock both screws
on the connector to ensure firm grounding. The connector information is as follow:
1
6
11 15
5
10
15 - Pin Color Display Signal Cable
Pin No. Description Pin No. Description
1 Red Video 9 No Pin!
2 Green Video 10 Sync Ground
3 Blue Video 11 Not Used
4 Not Used 12 Serial Data for DDC
5 Ground 13 H-Sync.
6 Red Ground 14 V-Sync.
7 Green Ground 15 Serial Clock for DDC
8 Blue Ground
3. S-Video ( Y /C ): TV rear side : 4 pin Mini-DIN female
Component Video: TV rear side : RCA female ( Red / Blue / Green )
TV: TV rear side : IEC type female
AV: TVrearside :RCAfemale(Yellow)
AV/HDAudio: TVrearside :RCAfemale(Red/White)
PC Input audio: 3.5mm Stereo female
Audio Input for AV,S-Video, Component Video : RCA female ( Red / White )
Headphone 3.5mm female
Audio Output ( to external speaker )
4. Apply power to the display by turning the power switch to the "ON" position and allow about ten seconds
for Panel warm-up. The Power-On indicator lights "GREEN" when the display is on.
5. With proper signals feed to the display, a pattern or data should appear on the screen, adjust the
brightness and contrast to the most pleasing display, or press auto-adjust to get the best picture-quality.
6. This TV (with PC function) has power saving function following the VESA DPMS. Be sure to connect the
signal cable to the PC.
7. If your TV requires service, it must be returned with the power cord.

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4.2 Factory Preset Display Modes:
Analog RGB Signal Timing
Vertical Horizontal Sync Polarity Presence Screen Mode
Dots ×Lines Frequency
(Hz)
Frequency
(KHz) Horizontal Vertical Horizontal Vertical FULL (15:9)
720 ×400 70.1 31.5 NEG POS YES YES YES
59.9 31.5 NEG NEG YES YES YES
72.8 37.9 NEG NEG YES YES YES
640 ×480
75.0 37.5 NEG NEG YES YES YES
60.3 37.9 POS POS YES YES YES
72.2 48.1 POS POS YES YES YES
800 ×600
75.0 46.9 POS POS YES YES YES

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5. Front Panel Control Knobs
Power Key ⑦:Press to turn on or off the TV.
MENU Key ⑥:Press to show the OSD menu and exit OSD menu at the TV.
Down / Up Key ⑤④:Select the intended function by pressing these two keys, or switch the channels
in the TV mode.
+ /- Key ②③:Press to confirm your function selection and adjustment volume.
Source Key ①:Press to select your input source.

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6. Repair Flow Chart
1. No Power (No LED indicator)
Check power cord
and board interface
NG Plug in power cord and interface
Check F901, BD901 Replace F901 or BD901
Check the circuit
Check IC901 Q901 Replace IC901 or Q901
Check T901 Replace T901
Check D904, D905 Replace D904, D905
Replace Q903, ZD902,
IC903 IC902
Check Q903, ZD902, IC903 IC902
and relative circuit
Check Q906, IC905 and relative circuit
No Power
OK
NG
OK
NG
OK
NG
OK
NG
OK
NG
OK

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2. No Display (LED indicator green)
Check the source Reset source
Check LVDS cable
NG
Replace LVDS cable
Check 12V power supply Return to “1”
Check U406 Replace U406
Check panel Replace panel
Check main board power supply
Check I2C communication Repair I2C communication relative circuit
No display
OK
NG
OK
NG
OK
OK
NG
OK
NG
OK
NG