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LCD Troubleshooting
Topics to be covered
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Basic LCD Theory
Block Diagram
Cautions
PCB’s Interconnections
Troubleshooting Techniques
McAllen Magic Writer Jig (MMWJ)
On-line Tech Report
Core Return Reporting
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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
Polarizer
Color Filter
Electrode
Liquid Crystal
Glass Substrate
(TFT)
Polarizer
Diffuser
Backlight
• 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
Single
Lamp
Inverter
Circuit
• 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.
LCD Theory: The Polarizer
Light that is
passed by the
first polarizer.
Aligned the same as the
upper Polarizer.
Light that is
blocked by the first
polarizer.
Polarizers
90 degree shift in polarization
blocks the light transmission.
• 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.
LCD Theory: The Glass
Substrate (TFT)
Glass Substrate (TFT)
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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.
LCD Theory: Liquid Crystal
Liquid Crystal
Material
Light Source
• 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.
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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 LT17/23X576
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 highvoltage 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.
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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, before applying 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)
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When the DIGITAL SIGNAL PWB
is replaced or the DIGITAL
INPUT is not normal.
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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.
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This procedure is used to reset the digital input when you
are unable to receive digital signals.
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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)
Connector
PWB
Analog Signal PWB
Input
Power PWB
Audio Video
Front Control
Speaker
Receiver
PWB
Digital
Signal
PWB
Speaker
When powering on without rear cover, insure that IC3106 is covered with black
masking tape.
• 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.
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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?
No
Reconnect the
power cord
Test again
Yes
Is there a
separate AC
Adaptor?
Yes
Yes
Troubleshoot
or replace Main
PWBA
Test again
Troubleshoot
or replace PS
PWBA
Replace
adaptor
Test again
Test again
Test again
Is the output
in spec
No
No
Are the outputs
good from the PS
PWBA?
No
Yes
Troubleshoot
or replace Main
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)
Voltage name
Typ. Value
Remarks
B+
12V/24V
LT-17X576/LT-23x576
5V_SB
5V
CPU IC1016
5V_VCC
5V
DC supply when POWER is ON
5V_P
5V
source for IC1037
3.3V_AP
3.3V
ADC IC1018
VDDM
2.5V
DRAM IC1032
VDDMQ
2.5V
DRAM IC1032
EX-VD3_3
3.3V
IC1037
EX-VL1.8
1.8V
IC1037
EX-VA1.8
1.8V
IC1037
EX-VD1.8
1.8V
IC1037
PVDD
12V/24V
LCD panel
B+AUDIO
12V
Audio IC1027
No Picture Troubleshooting
Repair or replace
video circuit
Power is on but there is
no picture.
Test again
No
Can the On
Screen Menu be
shown?
Yes
Is the LVDS signal
supplied to the LCD
Panel?
Yes
Replace LCD
Panel
No
Yes
Are supply
voltages OK?
Yes
Is the backlight
on?
No
Go to backlight
troubleshooting
No
Repair supply
voltages
Test again
Picture Troubleshooting
LVDS Connector
• 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.
Picture Troubleshooting
Checking the LVDS signal
LVDS with full field color bar input
• 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.
Picture Troubleshooting
Checking the LVDS signal
LVDS with no input 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.
Picture Troubleshooting
Receiver PWB
Tuner
RF
Tuner
IF
Demod
Micon/
DIST
AV-Select
IC501
V
V/YC
AD
Convert
Main Video
YC
PIP Video
AD
Convert
Comb
2D YC Sep
IP Convert/
Scaler
Digital Enhance
OSD Mix
CPN
CPN
Select
DVI
DVI
Inverter for
Backlights
RGB
matrix
RGB
matrix
Video
PWB
Display unit
Panel
CPU
OSD
Gen
LVDS
LVDS Signal, 5V supply for backlight, and controls
Control
• 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?
No
Repair or
replace power
supply related
PWBAs
Test again
Reapir or
replace Main
PWBA
Test again
Yes
Is the backlight or
inverter receiving an
"ON" command?
Yes
Repair or replace
inverter or LCD
Panel Assy
No
• 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 can also 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?
Yes
No
Repair or replace
supply PWBAs
Repair or replace
audio circuit
PWBAs
Test again.
Test again
• 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.
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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)
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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.
McAllen Magic Writer Jig (3)
• 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.
D1 and D2
Note: The Red button must be pressed each time MMWJ is used.
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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
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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.
On-line Tech Report
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
We recommend that you enter the suffix letter of the model
you are servicing so proper documentation can be noted.
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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.