LCD_Troubleshooting

Prévia do material em texto

LCD Troubleshooting 
Topics to be covered
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
LCD Theory
The Layers Of The LCD Panel
Backlight
Diffuser
Polarizer
Color Filter
Electrode
Liquid Crystal
Glass Substrate 
(TFT)
Polarizer
• Here we can see the different layers that a 
LCD Panel is composed of along with the 
diffuser and the backlight. In most models 
all of these are combined and replaced as 
a unit if replacement is required. Each 
layer will be described in a bit more detail 
in the following slides. 
LCD Theory: The Back Light
Numerous small thin fluorescent tubes are used in order to create an even amount 
of light throughout the panel.
LCD Theory: The Backlight 
Inverter 
Circuit
Single 
Lamp
• Each individual fluorescent tube has its 
own ballast or inverter circuit. If one of 
these single backlights fails it is 
recommended that all be replaced or else 
not all of the lamps will emit the same 
brightness.
LCD Theory: The Diffuser
Multiple layers of 
diffusion material.
• To further scatter (diffuse) the light from 
the backlight, multiple layers of diffusion 
material are used to create an evenly 
illuminated picture. 
Aligned the same as the 
upper Polarizer.
90 degree shift in polarization 
blocks the light transmission.
Light that is 
passed by the 
first polarizer. Polarizers
Light that is 
blocked by the first 
polarizer.
LCD Theory: The Polarizer
• Here is a demonstration of how polarizing filters 
work. In this example the only light available is 0 
degrees out of phase with the polarizers and 90 
degrees out of phase with the polarizers. On the 
left the polarizers are aligned the same so that 
the light that passes through the upper filter will 
pass through the lower filter. The example on 
the right shows what will happen if the two filters 
are shifted by 90 degrees, no light will pass.
Glass Substrate (TFT)
LCD Theory: The Glass 
Substrate (TFT)
• This illustration demonstrates how the glass section of the LCD 
panel is constructed. For this part of the LCD theory explanation 
special note should be taken for the Thin Film Transistor (TFT) and 
the glass substrate. The TFT is created on the glass substrate and 
controls liquid crystal material. The storage capacitor in this example 
is part of the circuit with the TFT, it helps with the control of the liquid 
crystal. The TFT, Pixel Electrode, and Storage Capacitor are all part 
of the Alignment Layer, which as a whole control each pixel of the 
LCD panel through picture data that is supplied by the units external 
circuitry. LCD’s depend on thin film transistors (TFT). Basically, 
TFT’s are tiny switching transistors and capacitors. They are 
arranged in a matrix on a glass substrate. To address a particular 
pixel, the proper row is switched on, and then a charge is sent down 
the correct column. Since all of the other rows that the column 
intersects are turned off, only the capacitor at the designated pixel 
receives a charge. The capacitor is able to hold the charge until the 
next refresh cycle. And if we carefully control the amount of voltage 
supplied to a crystal, we can make it untwist only enough to allow 
some light through. 
• The Common Electrode is also part of this control circuit and will 
covered in a few slides.
Liquid Crystal 
Material
Light Source
LCD Theory: Liquid Crystal
• This is where the Liquid Crystal Material is 
found in the cell structure. When the 
Alignment Layer applies a voltage to the 
Liquid Crystal it will twist. Depending upon 
the amount of voltage and twist it will allow 
differing amounts of light to reach the 
Color Filter side of the panel assy.
LCD Theory: Liquid Crystal
• The illustration on the right shows the display in the “off”
state. There is no signal (voltage) applied to the 
electrodes so the Liquid Crystal allows the light to pass 
directly through with no polarity change but since the 
second polarized panel is rotated 90 degrees the light 
does not pass through.
• The illustration on the left shows the display in the “on”
state. There is signal (voltage) applied to the electrodes 
so the Liquid Crystal twists 90 degrees end to end which 
in turn twists the light 90 degrees. This allows the light to 
pass through the second polarized panel. The twisted 
popsicle stick stack is an interesting way of thinking of 
how the Liquid Crystals twist.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
System Block Diagram LT-17X576
• This is the overall system block diagram. 
Interconnection PWB’s is the Tuner, A/V 
Jack PWB, speakers, key pad, IR sensor, 
and the LCD panel. Models that reflects 
these next three slides are the LT-
17/23X576
Video Signal and PC RGB LT-17X576
• This slide shows the video signal and PC/RGB 
communication. The DDR memory IC1032 is 
connected to the Video select/YC sep/RGB 
process/LVDS format converter IC1037(SVP 
EX52) this IC receives A/V signals from the A/V 
Jack PWB and converts the signals to LVDS 
format to display on the LCD. IC1018 (AD9883) 
is the A-D converter that takes your PC/RGB 
signals and converts the analog signals to digital 
for IC1037 (SVP EX52). 
Audio Signal LT-17X576
• The MSP3440 (IC1033) receives the audio 
signals from the AV Jack PWB and sends 
these processed audio signals to 
TPA1517 (IC1027) for amplification.
LT-26WX84 (LCD PANEL PWBs)
• Internally, LCM has additional boards: 
INVERTER and MAIN CTL Board. The 
INVERTER board is responsible for converting 
16VDC to 900VAC to turn on the 
FLUORESCENT BACKLIGHT. For the 
INVERTER to turn, B/L ON, PWM and ANALOG 
DIM voltage controls must be present. 
• MAIN CTL board controls source/gate driver IC 
turning the TFTs on influencing the twisting 
movement of the liquid crystal.
LT-26WX84 (INVERTER & MAIN CTL BD)
• For the INVERER BOARD to turn ON, 3 controls 
must be present: BL ON, PWM DIM, ANA DIM. 
BL ON must be 5V. PWM DIM controls the 
brightness of the BACKLIGHT by changing its 
duty cycle ratio of its Pulse Width signal. 
ANALOG DIM must also be present. Both PWM 
DIM and ANA DIM are dependent on the setting 
the ENERGY SAVER MODE: DARKER or 
BRIGHTER. To extend the life of the 
BACKLIGHT, the backlight intensity can be set 
to DARKER in the MENU SETTING.
LT-26WX84 (INVERTER PWB)
LT-32WX84 (INVERTER & LCD MAIN CTL BOARD)
• LT-32WX84 has 2 inverters. One for the upper 
half and another for the lower half. Therefore, if 
the either half is darker then it could be assumed 
that the INVERTER is defective. For this model, 
16V is supplied from the PS board. 
• If the fuse/s are defective, because of the high-
voltage handled on the inverter, it is 
recommended to replace the complete 
INVERTER PWB. 
Block Diagram LT-26X576
• This slide is intended to assist you in the 
Video and Audio signal flow.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
Disassembly Caution (1)
When powering on without rear cover, disconnect the DVI/HDMI 
module.
• THIS IS IMPORTANT. To prevent the 
HDMI module from becoming invalid, 
before applying power, remove the two 
power plugs from their connectors. 
Working with the back off, the unit can 
now be powered. 
• Models: LT-26WX84
Disassembly Caution (2)
When powering on without rear cover, insure that IC3106 is covered with 
black masking tape.
• This is important: To prevent the digital input from 
becoming invalid, beforeapplying power, cover IC3106 
with black masking tape. Working with the back off the 
unit can now be accomplished. 
• Models:
• LT-26X575 LT-26X576 LT-40X776
• LT-26X585 LT-26X776 LT-32X576
• LT-32X575 LT-32X776
• LT-32X585 LT-37X776
• For Models LT-17/23X475 and LT-17/23X576 no digital 
reset is needed because these models DO NOT have 
HDCP.
DVI Photosensor
Activation of Photo-sensor can be prevented by covering it with a piece of black 
electrical tape from ambient light 
Disassembly Caution (3)
• When the DIGITAL SIGNAL PWB 
is replaced or the DIGITAL 
INPUT is not normal.
• Set to 0 minutes using the [SLEEP 
TIMER] key.
• Press the [VIDEO STATUS] key and 
[DISPLAY] key simultaneously, then 
enter the SERVICE MODE.
• When the Main Menu is displayed, 
press [2] key to enter the self check 
mode.
• Turn off the power by pressing the 
[POWER] key on the remote control 
unit.
This procedure is used to reset the digital input when you 
are unable to receive digital signals.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
PCB’s Interconnections (1)
• PC identification and location for model 
numbers:
• LT-17/23X475
• LT-17/23/576
PCB’s Interconnections (2)
When powering on without rear cover, insure that IC3106 is covered with black 
masking tape.
Receiver 
PWB
Pow
er PW
B
Speaker Speaker
Digital 
Signal 
PWB
A
udio V
ideo Input
Analog Signal PWB
Front C
ontrol
Connector
PWB
• This the PCB interconnection for the following 
models:
• LT-26X575/585/576
• LT-32X575/585/576
• Note: these models do not have fans as it was 
with the LT-26WX84 and WX74.
• Boards are from Samsung and the panel is 
manufactured from Sharp.
• When panel is determined to be defective panel 
is replaced as complete unit.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
Problem Diagnosis and 
Troubleshooting 
No Power 
No Picture
No Backlight
No Sound
Trouble shooting an LCD unit can be broken down into 4 basic 
sections, No Power, No Picture, No Backlight, No Sound. There could 
be many other types of problems but these are the basic 4 symptoms 
that are experienced.
LT-17X576
• This slide and the following slide represent just two of 
the five or more different block diagrams that can be 
found in LCD models released in the last year. The block 
diagrams are a always a good place to start getting 
familiar with the model and start your trouble shooting. 
• Notable differences between this block diagram and the 
next diagram are the inverter board on this diagram and 
the internal PS of the next diagram. The following 
diagram’s model has the inverter built into the LCD 
Panel Assy while this diagram’s model has an external 
PS.
LT-26X466
No Power Troubleshooting
Power LED
does not come
on
Is the power cord
connected?
Is there a
separate AC
Adaptor?
Reconnect the
power cord Test again
Test again
Test again
Replace
adaptor
Troubleshoot
or replace Main
PWBA
Test again
Troubleshoot
or replace Main
PWBA
Test again
No
Yes
Yes
No
Is the output
in spec
Yes
No
No
Yes
Are the outputs
good from the PS
PWBA?
Troubleshoot
or replace PS
PWBA
PANEL_ON (PVDD)(LT-17/23X576)
When power on is initiated Q009 provides gate supply to turn on 
the MosFET and provide PVDD
Voltage Table (LT-17/23X576)
Audio IC102712VB+AUDIO
LCD panel12V/24VPVDD
IC10371.8VEX-VD1.8
IC10371.8VEX-VA1.8
IC10371.8VEX-VL1.8
IC10373.3VEX-VD3_3
DRAM IC10322.5VVDDMQ
DRAM IC10322.5VVDDM
ADC IC10183.3V3.3V_AP
source for IC10375V5V_P
DC supply when POWER is ON5V5V_VCC
CPU IC10165V5V_SB
LT-17X576/LT-23x57612V/24VB+
RemarksTyp. ValueVoltage name
No Picture Troubleshooting
Power is on but there is
no picture.
Can the On
Screen Menu be
shown?
 Yes
Is the backlight
on?
No
No
Go to backlight
troubleshooting
Repair or replace
video circuit
Yes
Is the LVDS signal
supplied to the LCD
Panel?
Yes
Replace LCD
Panel
No
Are supply
voltages OK?
Repair supply
voltages Test again
No
Yes
Test again
LVDS Connector
Picture Troubleshooting
• This is a pin description of the Low Voltage 
Digital Signaling connector.
• The important connections that I will point out 
are pins 7,8, and 9 – the analog dimming, PWM 
dimming and backlight on/off control. 
• The presence of video riding in the LVDS signal 
can be checked at pins 12, 13, 20, 21, 24, and 
25. The signal will appear to be similar to the 
RF waveform of a VCR, with the incoming video 
signal being modulated by that carrier.
Signal flow 
• This an excerpt from LT-32X84 showing 
the signal from the VIDEO to DIGITAL 
SIGNAL board. Since formatting, scaling 
and LVDS conversion is performed on the 
DIGITAL SIGNAL board, the LVDS is from 
CN000X.
LVDS (LT-17/23X576)
LVDS outputs are from IC1037 (LVDS/FORMATTER IC). Panel power supply is 
derived from PVDD (12V for LT-17X576 or 23V for LT-23X576).
LVDS Test point 
LVDS TP is at Digital BD CN000X. For the sake of showing the connector 
clearly, the flex cable between CN900H of the DIGITAL board and CNH of the 
Analog board was removed.
LVDS with full field color bar input
Picture Troubleshooting
Checking the LVDS signal
• Pictures captured with 600MHz storage 
scope. The scope probe was placed on a 
random LVDS connector pin with a Full 
Field Color Bar input.
• Note that the pictures look different due to 
the time per division settings.
LVDS with no input signal
Picture Troubleshooting
Checking the LVDS signal
• Pictures captured with 600MHz storage 
scope. Here the Full Field Color Bar input 
signal has been removed. 
• This check will verify whether or not the 
video signal is reaching the LCD panel.
Panel
Inverter for
B
acklights
Control
LVDS Signal, 5V supply for backlight, and controls
Tuner
Tuner IF DemodRF
V
YC
DVI
Main Video
AV-Select
IC501
DVI
V/YC AD
Convert
Comb
RGB
matrix
AD
Convert
RGB
matrix
IP Convert/
Scaler
Digital Enhance
OSD Mix
CPU
OSD
Gen
LVDS
Receiver PWB
Display unit
PIP Video
CPN
CPN
Select
Video
 PWB 2D YC Sep
Micon/
DIST
Picture Troubleshooting
• Here is a diagram that demonstrates the 
flow of video input circuit up to the LCD 
panel. In the process of troubleshooting a 
no video problem it may need to be 
determined where in the video circuit a 
failure has occurred.
No Backlight Troubleshooting
Continued From No
Picture Trouble
Shooting
Are Backlight and
power supply
voltages good?
Repair or
replace power
supply related
PWBAs
Test again
Is the backlight or
inverter receiving an
"ON" command?
Reapir or
replace Main
PWBA
Test again
Repair or replace
inverter or LCD
Panel Assy
No
No
Yes
Yes
• No Backlight troubleshooting. In order to 
light the LCD panel three conditions must 
be met (1) confirm that the VCC to panel 
(normally 12V could be 24V) is present (2) 
Panel ON command is present and (3) 
dimming command is OFF.
No Backlight Troubleshooting
By shining a flashlight into the screen you can check to see if picture data is on the 
LCD Panel when the backlight is not operating.
• One more method of troubleshooting a no 
picture/no backlight problem is to check for a 
picture on the screen by shining a flashlight 
directly into the screen, in effect substituting the 
flashlight for the backlight. If the LCD panel and 
video circuits are working properly and the 
backlight is not, then you should be able to see 
the picture faintly on the screen by shining a 
flashlight directly into the screen. 
• In order to take pictures of this a very large 
flashlight was used. 
No Backlight Troubleshooting
• The “Panel On” command is quite 
common to find in the diagrams and is one 
item to check when the backlight does not 
come one.
• We canalso see that some panels will use 
12V and others will use 24V for the 
backlight.
No Audio Troubleshooting
Picture is OK but
there is no Audio
Are supply
voltages good?
Repair or replace
supply PWBAs
Test again.
Repair or replace
audio circuit
PWBAs
Test again
Yes
No
• This information was sourced from the 
Tatung factory training class held in 
McAllen. This applies to the following:
• LT-17/23X475
• LT-17/23X576 
Flash Rom Re-Initialization
Use this procedure for: 
•Flash Rom Replacement
•Board Swap
•Intermittent or constant symptoms including :
Key functions do not work. 
Unit does not power up.
Remote control does not work.
Procedure:
•Re-seat Flash Rom IC1004 (LT-17/23X475) or ICI026 (LT-17/23X576). 
•Check for cold solders on the socket and re-solder as needed.
• Press the menu, ch+, and ch- buttons together at the same time for no more than 
20 seconds. If successful the re-initialization screen will appear on the LCD 
screen.
• The following pictures and all of the LCD 
panel failure pictures in the following slides 
are thought to be LCD Panel failures.
Failure Pictures
Missing color
Failure Pictures
Line in picture
Failure Pictures
Missing color, possible backlight problem.
Failure Pictures
Possible backlight problem
Failure Pictures
Line in picture
Failure Pictures
Backlight problem, possible color problem
Failure Pictures
Backlight problem, possible color problem
Failure Pictures
Vertical lines in the picture
Failure Pictures
Vertical line in the red only
Failure Pictures
It looks like one or two colors are always on
LT-26WX84 Polarizer 
Typical failure on LT-26WX84 with the polarizer being defective. Generally, 
characterized by horizontal black bands when displaying a white signal. This usually 
happens on industrial applications where extended usage is the norm. For example, 
restaurants, gymnasiums, airports. LCM QLD0282-002.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
McAllen Magic Writer Jig (1)
• Purpose of JIG is 
to edit data 
causing HDMI 
incompatibilities 
with Cable Set Top 
Box or DVD player.
• Symptoms include 
No video, No 
audio, and aspect 
ratio changing.
• The MMWJ is used to edit data values in the 
EEPROM for HDMI incompatibilities when the 
LT-26/32/37/40X776 are connected to DVD 
players or Set Top Boxes such as the DISH 
Satellite DVR942, 811, and the 211. Symptoms 
include loss of audio, noisy audio, loss of video, 
noisy video, or aspect ratio changing. These are 
the only known LT models in which there is an 
HDMI incompatibility.
McAllen Magic Writer Jig (2)
• Install MMWJ software . 
Software and Instructions for 
MMWJ can be downloaded 
from iSee. (refer to model 
number)
• MMWJ program can operate 
with Windows 98, Win2K, and 
WinXP. (These windows 
operating systems are the only 
ones that have been confirmed 
to operate the MMWJ 
program) 
• Connect USB “A” connector 
cable to computer.
USB "A" connector
USB “B" connector
• In order to use the MMWJ ASC must 
download software and instructions. (go to 
www.jvcservice.com refer to the model 
number of the unit on iSee) Follow the 
installation instructions to enable use of 
the MMWJ program. This slide shows the 
two ends of the USB Universal Serial Bus 
cable. After software installation connect 
USB “A” connector to USB port of the PC.
• Press the red button as the USB 
“B” connector cable is inserted to 
the MMWJ. (The red button must 
be pressed in order to enable PC 
and JIG communication)
• PC will request Driver for USB 
cable. (Refer to MMWJ 
instructions for installation)
• After USB Driver installation 
LEDs D1 and D2 will light to 
confirm communication.
• Refer to TT-06090701-T(R3) for 
HDMI incompatibility correction.
McAllen Magic Writer Jig (3)
Note: The Red button must be pressed each time MMWJ is used.
D1 and D2
• While the red button is pressed insert the USB “B” connector to the 
MMWJ pop-up screen will appear on your PC requesting driver 
installation. (Follow the instructions on the MMWJ instruction book 
for driver installation) when the driver installation is complete D1 and 
D2 of the MMWJ will light to indicate that the MMWJ is ready for
use. To edit data for HDMI incompatibility follow the instructions as 
stated on TT-06090701-T(R3) bulletin. As stated on slide you must 
press the red button when connecting MMWJ to your PC each time 
the software is opened for use.
• Model numbers that are affected:
• LT-26X776
• LT-32X776
• LT-37X776
• LT-40X776
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
• The following slides are to assist you on how to 
enter tech reports and for core returns when 
servicing JVC products.
• All ASC are given a User ID and Password to 
gain access of iSee where JVC products 
information is stored such as service manuals, 
tech tips and service diagrams. Firmware and 
software information is also available on iSee. 
When servicing a JVC product always refer to 
iSee for the model information such as upgrades 
and tech reports. 
Go to Web-Site
Enter User ID and Password
On-line Tech Report
Go to iSee Database
On-line Tech Report
Click on Tech Tip Entry
On-line Tech Report
On-line Tech Report
We recommend that you enter the suffix letter of the model 
you are servicing so proper documentation can be noted.
• Basic LCD Theory
• Block Diagram
• Cautions
• PCB’s Interconnections
• Troubleshooting Techniques
• McAllen Magic Writer Jig (MMWJ)
• On-line Tech Report
• Core Return Reporting
Core Return Reporting
Core return form must be filled out in order to receive core credit. 
Include model number, serial number, and symptom. The more 
information that is included the better to evaluate and determine cause 
of failure.
Core Return Reporting
Provide information as stated on form. Include as much information as 
possible to help assist in core repairs.