LCD Trouble Shooting 2006(R6 )PDF - rtvcenter.comfound in LCD models released in the last year. The block diagrams are a always a good place to start getting familiar with the model

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


LCD TheoryThe 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.


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.


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


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


• 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.


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

Power PW

BSpeaker Speaker

Digital Signal PWB

Audio V

ideo Input

Analog Signal PWB

Front Control

ConnectorPWB

• 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.


Problem Diagnosis and Troubleshooting

No Power

No Picture

No Backlight

No SoundTrouble 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 LEDdoes not come

on

Is the power cordconnected?

Is there aseparate AC

Adaptor?

Reconnect thepower cord Test again

Test again

Test again

Replaceadaptor

Troubleshootor replace Main

PWBATest again

Troubleshootor replace Main

PWBATest again

No

Yes

Yes

No

Is the outputin spec

Yes

No

No

Yes

Are the outputsgood from the PS

PWBA?

Troubleshootor 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 isno picture.

Can the OnScreen Menu be

shown? Yes

Is the backlighton?

No

No

Go to backlighttroubleshooting

Repair or replacevideo circuit

Yes

Is the LVDS signalsupplied to the LCD

Panel?

Yes

Replace LCDPanel

No

Are supplyvoltages OK?

Repair supplyvoltages 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 TroubleshootingChecking 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 TroubleshootingChecking 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 forB

acklights

Control

LVDS Signal, 5V supply for backlight, and controls

Tuner

Tuner IF DemodRF

V

YC

DVI

Main Video

AV-SelectIC501

DVI

V/YC ADConvert

Comb

RGBmatrix

ADConvert

RGBmatrix

IP Convert/Scaler

Digital Enhance

OSD Mix

CPU

OSDGen

LVDS

Receiver PWB

Display unit

PIP Video

CPN

CPNSelect

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 NoPicture Trouble

Shooting

Are Backlight andpower supply

voltages good?

Repair orreplace powersupply related

PWBAs

Test again

Is the backlight orinverter receiving an

"ON" command?

Reapir orreplace Main

PWBATest again

Repair or replaceinverter 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.


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.


• 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 butthere is no Audio

Are supplyvoltages good?

Repair or replacesupply PWBAs

Test again.

Repair or replaceaudio 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-InitializationUse 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.


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.


• 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.


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 foruse. 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


• 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.


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.

Documents

LCD Trouble Shooting 2006(R6 )PDF - rtvcenter.comfound in LCD models released in the last year. The block diagrams are a always a good place to start getting familiar with the model