AOC LT2725 Service Manual
27’’ LCD TV Color Monitor Norcent LT2725
Service
Service
Service
Horizontal Frequency
31- 60 KHz
Description Page Description Page
Table Of Contents.......…….…..............................…........1
Revision List.…….….....................................……......2
Important Safety Notice.……..................……......3
1. Monitor Specification..…............................………........4
2. Operating Instructions……...……………….……….......5
2.1 The Use Of Remote Control..…………..................5
2.2 Front Panel Control Knobs.....................…...........6
2.3 OSD Operating…………….…............……...............7
2.4 How To Connect...………........................…............12
3. Input/Output Specification............……………............15
3.1 Input Signal Connector............………….................15
3.2 Factory Preset Display Modes........………...............16
4. Mechanical Instructions..………....……......................17
5. Repair Flow Chart…….……………………..................22
6. White Balance, Luminance Adjustment…...……….....25
7. PCB Layout………….....…………………...….…….....27
ANY PERSON ATTEMPTING TO SERVICE THIS CHASSIS MUST FAMILIARIZE HIMSELF WITH THE
TABLE OF CONTENTS
7.1 Main Board………….....……………………....….......27
7.2 Power Board………..….…………………….....….......29
7.3 Audio Board…………..…..........................…….........31
7.4 Key Board.......………..…...…...................................32
8. Block Diagram..…….…....................….......................33
8.1 Main Board.............………..……...............................33
8.2 Power Board….............……...….…..........................34
9. Schematic Diagram...……....….………………….......35
9.1 Main Board……...…..……..…………......................35
9.2 Power Board...…….….……….……………………...53
9.3 Audio Board...………………………..………………..54
9.4 Key Board......…...............…………........................55
9.5 IR Board...…….........………..…..............................56
9.6 Side Board……………………....…………………….57
10. Exploded View……...................................................58
11. BOM List……………….……………...……….…........59
SAFETY NOTICE
CHASSIS AND BE AWARE OF THE NECESSARY SAFETY PRECAUTIONS TO BE USED WHEN SERVICING
ELECTRONIC EQUIPMENT CONTAINING HIGH VOLTAGES.
CAUTION: USE A SEPARATE ISOLATION TRANSFOMER FOR THIS UNIT WHEN SERVICING
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27’’ LCD TV Color Monitor Norcent LT2725
Revision List
Version Release Date Revision History TPV Model
A00 Jun-05-2006 Initial Release E276MZNKD2NCNCP
A01 Nov-07-2006 Add TPV Model in item 11 E276MZNKD2NCNP
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27’’ LCD TV Color Monitor Norcent LT2725
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.)
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27’’ LCD TV Color Monitor Norcent LT2725
1. General Specifications
27” 16:9 LCD DISPLAY PANEL
Resolutions: 1366 (H) X 768 (V) pixels, (1 pixel = 1 R, G, B cells)
0.1460 mm (H) X 0.4365 mm(V) pixel pitch.
Panel MAX Brightness: 550 cd/m2 ㎡ , Panel MAX Contrast:1000:1
ATSC receiver, MPEG-2 decoder
NTSC receiver, Video decoder
Video, S-Video receiver
MIPS controller technology
Factory Presets
D-SUB Vertical refresh rate 56Hz to 75 Hz
D-SUB Horizontal frequency 31.5KHz to 64KHz
Universal Power Supply designed for worldwide application
UL, FCC, certification
≤150 W (Power consumption)
Closed Caption / V-chip For USA
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27’’ LCD TV Color Monitor Norcent LT2725
2. Operations Instructions
2.1 The Use Of Remote Control
Remote control button function as follow
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27’’ LCD TV Color Monitor Norcent LT2725
2.2 Front Panel Control Knobs
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27’’ LCD TV Color Monitor Norcent LT2725
2.3 OSD Operations
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
2.4 How To Connect
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
3. Input/Output Specification
3.1 Input Signal connector
This procedure gives you instructions for installing and using the LCD TV display.
Lay 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.
Connect the 15-pin D-SUB 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:
15 - Pin Color Display Signal Cable
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Pin Signal Assignment Pin Signal Assignment
1 Red Video 9 No Pin!
2 Green Video 10 Sync. Ground
3 Blue Video 11 SDA (Remote Control)
4 SCL (Remote Control) 12 Serial Data for DDC
5 GROUND 13 Horizontal Sync.
6 Red Video Ground 14 Vertical Sync.
7 Green Video Ground 15 Serial Clock for DDC
8 Blue Video Ground
HDMI Digital connector pin assignments
1
11 15
5
10
Pin Signal Assignment Pin Signal Assignment
1 TMDS Data2+ 2 TMDS Data2 Shield
3 TMDS Data2- 4 TMDS Data1+
5 TMDS Data1 Shield 6 TMDS Data1-
7 TMDS Data0+ 8 TMDS Data0 Shield
9 TMDS Data0- 10 TMDS Clock+
11 TMDS Clock Shield 12 TMDS Clock-
13 CEC 14 NC
15 SCL 16 SDA
17 DDC/CEC Ground 18 +5V Power
19 Hot Plug Detect
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27’’ LCD TV Color Monitor Norcent LT2725
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.
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.
This TV (with PC function) has power saving function following the VESA DPMS. Be sure to connect the signal
cable to the PC.
If your TV requires service, it must be returned with the power cord.
3.2 Factory Preset Display Modes:
Analog RGB input signal timing
VESA MODES
Horizontal Vertical
Nominal
Mode Resolution Total
640x480@60Hz 800 x 525 31.469 N 59.940 N 25.175
VGA
SVGA
XGA 1024x768@60Hz 1344x806 48.363 N 60.004 N 65.000
WXGA 1360x768@60Hz 1792x795 47.712 P 60.015 P 85.5
640x480@72Hz 832 x 520 37.861 N 72.809 N 31.500
640x480@75Hz 840 x 500 37.5 N 75 N 31.500
800x600@56Hz 1024 x 625 35.156 P 56.25 P 36.000
800x600@60Hz 1056 x 628 37.879 P 60.317 P 40.000
800x600@72Hz 1040 x 666 48.097 P 72.188 P 40.000
800x600@75Hz 1056 x 625 460875 P 75 P 49.5
Frequency
(KHz)
Sync
Polarity
Nominal
Freq.
(Hz)
Sync
Polari
ty
Nominal
Pixel
Clock
(MHz)
HDMI input signal timing
VESA MODES
Mode Resolution Total
720P
1080i
480P
1280×720P
1920X1080i 33.75 60 74.25
720X480P 31.54 60 27.00
45.00 60 74.25
Horizontal Vertical
Nominal
Frequency
(KHz)
Polarity
Sync
Nominal
Freq.
(Hz)
Sync
Polarity
Nominal
Pixel
Clock
(MHz)
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27’’ LCD TV Color Monitor Norcent LT2725
4. Mechanical Instructions
Step Figure Description
Lay the
LCD-TV on a
Preparation
flat, soft and
clean
surface.
Remove
base
Remove
back cover
Remove
seven screws
Remove four
screws
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27’’ LCD TV Color Monitor Norcent LT2725
Remove
shield
Remove
connector
Remove
fifteen
screws
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27’’ LCD TV Color Monitor Norcent LT2725
Remove
Main,
power
and Audio
board
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Remove
screws and
disconnect
the wire
harness
27’’ LCD TV Color Monitor Norcent LT2725
Remove
twelve
screws
Remove
main frame
Remove
key board
Remove four
screws (left
and right)
Remove two
screws
Remove
panel
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Remove four
screws
27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
5. Repair Flow Chart
5.1 Abnormal display
CHECK CON901 PIN9＝12V
CON905 PIN3=5V?
NG
Check POWER BOARD
OK
CHECK CN407 PANEL connect is
normal?
NG
Reconnect CN407
OK
CHECK X401、X701 is normal?
NG
Check surge circuit
OK
CHECK U401 PIN R5、PIN T8=3.3V?
U401 PIN E6=2.5V? PIN R9=1.8V?
OK
CHECK U108 PIN18, PIN17, PIN14 output wave is OK;
PIN9 PIN20 power supply is OK?
OK
CHECK I²C1DATA, CLK is normal?
OK
CHECK SCALER HS VS is normal?
OK
Check TV mode display is normal?
NG
OK
CHECK SCALER power
OK
Check Tuner circuit
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27’’ LCD TV Color Monitor Norcent LT2725
pply
5.2 No sound
Check speakers are ok?
OK
Check earphone is normal?
OK
Check Q2 MUTE circuit
OK
Test NJM2199 (U5) PIN 12 PIN
11 output is normal?
Test TC200 (U2) PIN9 PIN10 PIN11
PIN 12 is normal
OK
OK
OK
NG
NG
Check TPA6110A2 (U600)
Relative circuit is normal?
Check CS4335 (U405) PIN5
PIN 8 output is normal?
Check NJM2199 (U5) PIN8 power
supply is normal?
OK
NG
OK
Check TC200 (U2) PIN21
power supply is normal?
Test TP2050 (U1) PIN17 PIN10 PIN8
PIN2 Output is normal?
CHECK X701 surge is normal?
Check CAS-220/CS (U701) is
normal?
Check SF701 PIN5、4 signal
input is normal?
OK
OK
OK
OK
NG
NG
Check TP2050 (U1) PIN15 PIN7 PIN4
power supply is 20V; PIN23 PIN25 power
su
is 5V?
OK
NG
Check ZR39660BGCG (U401) is normal?
Check TUNER circuit
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27’’ LCD TV Color Monitor Norcent LT2725
5.3 Key Board
OSD is unstable or not working
N
Is Key Pad Board connecting normally?
Y
Connect Key Pad Board
Is Button Switch normally?
Y
Is Key Pad Board Normally?
Y
Check Main Board
N
N
Replace Button Switch
Replace Key Pad Board
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27’’ LCD TV Color Monitor Norcent LT2725
6. White Balance, Luminance Adjustment
Approximately 30 minutes should be allowed for warm up before proceeding white balance adjustment.
First adjust PC mode and then adjust AV mode, HDMI mode, component 480i mode, component 480p mode. Before
started adjust white balance, please set the Chroma-7120 MEM. Channel 01 to Cold color MEM. and channel 03 to
Normal color, MEM. and channel 04 to warm color, MEM.(Our cold parameter is x = 291, y =306; normal parameter
is x =299, y =315; warm parameter is x =308, y =325)
Color Temp. Cold Normal Warm
x 291 299 308
PC MODE
AV MODE
HDMI
COMPONENT
（480i/480p）
Note: The tolerance of the color coordinates should be less than ± 20.
How to setting MEM. channel you can reference to Chroma-7120 user guide or simple use “ SC” key and “ NEXT”
key to modify x, y , Y value and use “ID” key to modify the TEXT description
Following is the procedure to do white-balance adjust
Note: Step of AV, HDMI, COMPONENT480i, COMPONENT480p mode adjustment is the s ame as PC mode,
PC mode:
Ⅰ. In the TV mode adjust volume to zero and press number key 9 Æ 8 Æ 7 Æ 6. It will achieve the
factory mode. Select the item of White Balance and press right key to enter it.
In the White Balance you can adjust 8 items.
1-3 items is RO, GO, BO Æ R, G, B Bias adjust.
4-6 items is RG, GG, BG Æ R, G, B Gain adjust.
7 item needn’t adjust
8 items is color temperature select: Cool, Normal, and Warm.
Ⅱ. Bias (Low luminance) adjustment:
1. Set the raster pattern (Black pattern with 1024×768) Input.
2. Adjust the brightness on OSD until chroma 7120 measurement reach the lowest value.
Ⅲ. Gain adjustment:
A. Adjust Cold color-temperature:
1. Set the Contrast of OSD function to 80 and Adjust Brightness to chroma-7120 Y>350 cd/m2
2. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
3. Switch the MEM. channel to Channel 01 (with up or down arrow on chroma-7120)
4. The LCD-indicator on chroma-7120 will show x =291, y =306, Y>350cd/m2
5. Adjust the 4 item: RG, until chroma 7120 indicator reached the value R=100
6. Adjust the 5 item: GG, until chroma-7120 indicator reached the value G=100
7. Adjust the 6 item: BG, until chroma-7120 indicator reached the value B=100
8. Repeat above procedure until chroma-7120 RGB value meet the tolerance =100±2
9. Switch the chroma-7120 to x, y, Y mode with press “MODE” button to check the color temp is in SPEC. or not.
10. Enter the 8 item to select another color temperature to adjust.
y 306 315 325
Y 350 350 350
x 291 299 308
y 306 315 325
Y 450 450 450
x 291 299 308
y 306 315 325
Y 420 420 420
x 291 299 308
y 306 315 325
Y 450 450 450
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27’’ LCD TV Color Monitor Norcent LT2725
B. Adjust Normal color-temperature:
1. Set the Contrast of OSD function to 80 and Adjust Brightness to chroma-7120 Y>350cd/m2
2. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
3. Switch the MEM. channel to Channel 03 (with up or down arrow on chroma-7120)
4. The LCD-indicator on chroma-7120 will show x =299, y =315, Y>350cd/m2
5. Adjust the 4 item: RG, until chroma 7120 indicator reached the value R=100
6. Adjust the 5 item: GG, until chroma-7120 indicator reached the value G=100
7. Adjust the 6 item: BG, until chroma-7120 indicator reached the value B=100
8. Repeat above procedure until chroma-7120 RGB value meet the tolerance =100±2
9. Switch the chroma-7120 to x, y, Y mode With press “MODE” button to check the color temp is in SPEC. or not.
10. Enter the 8 item to select another color temperature to adjust.
C. Adjust Warm color-temperature:
1. Set the Contrast of OSD function to 80 and Adjust Brightness to chroma-7120 Y>350cd/m2
2. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
3. Switch the MEM. channel to Channel 04 (with up or down arrow on chroma-7120)
4. The LCD-indicator on chroma-7120 will show x =308, y =324, Y>350cd/m2
5. Adjust the 4 item: RG, until chroma 7120 indicator reached the value R=100
6. Adjust the 5 item: GG, until chroma-7120 indicator reached the value G=100
7. Adjust the 6 item: BG, until chroma-7120 indicator reached the value B=100
8. Repeat above procedure until chroma-7120 RGB value meet the tolerance =100±2
9. Switch the chroma-7120 to x, y, Y mode With press “MODE” button to check the color temp is in SPEC. or not.
10. Enter the 8 item to select another color temperature to adjust.
Ⅳ.Switch different source:
Press the source key on the remote control to switch different source to adjust the AV, HDMI, CONPONENT 480i
and COMPONENT 480p mode.
Press “Exit” button on remote control to quit from factory mode.
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27’’ LCD TV Color Monitor Norcent LT2725
7. PCB Layout
7.1 Main Board
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27’’ LCD TV Color Monitor Norcent LT2725
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27’’ LCD TV Color Monitor Norcent LT2725
7.2 Power Board
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27’’ LCD TV Color Monitor Norcent LT2725
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