LCD PanelService Training

2008TS-08051301-T

Hello and Welcome to JVC’s LCD Panel Troubleshooting Guide. This guide is intended to help you assess problems related to the LCD Panel Electronic Boards. This also serves as a guide to discovering the failures of the TV Electronic Boards as well.

Before you begin any troubleshooting, review the TV Model’s Service Manual and Service Bulletins. These items may show information relevant to the repair.

Also, if at any time you have difficulty proceeding with steps or questions regarding the repair, contact JVC Tech Support or you Local JVC Field Engineer for assistance.

COURSE OVERVIEW

6. Inverter PWB Troubleshooting

7. Backlight/Diffuser

8. Flowchart

9. Examples

1. Service Information

2. The LCD Panel

3. Block Diagrams

4. Control PWB Troubleshooting

This presentation will cover items that will assist in the Troubleshooting of faults related to the LCD panel and it'sPWBs and components.

Different Version Identified Here

LT-32E488 Version “SAA” LT-32E488 Version “VAA”

“SAA” Version uses

QLD0495-001-JIM LCD Panel

“VAA” Version uses

QLD0527-002-JIM LCD Panel

SERVICE INFORMATIONModel Identification

Prior to service, it is always wise to verify the Model and Version to ensure that the correct Service manuals and Schematics are being used.

The pictures show the LT-32E478 Versions “SAA” and “VAA”.

One of the differences in the (2) models is the LCD Panel used in the TV. There are other differences between the models that were not explained.

Version differences may include LCD Panel, PWB or Circuit Designdifferences.

The Model Number listed at the top of the model label will always be the same for all versions.

To find the Model Version it is necessary to look to the right of the Model Number. This may vary at times, but will always be shown in the Service Manual.

THE LCD PANELComponents of The LCD Panel

Backlight

Inverter(s)Control PWB

LCD Panel (Cell and Drive PWBs)The LCD Panel Assembly consists of (x4) major components.

1. Control PWB – inputs LVDS signal from the TV’s Video PWBs and outputs Drive Signals to the LCD Panel

2. LCD Panel – Horizontal Gate and Vertical Source Drives on the LCD Panel create the displayed video image

3. Inverter PWBs – Power the Backlight. LCD Panel Assemblies may have (x1) or (x2) Inverter PWBs.

4. Backlight – Provides light and allows the LCD Panel image to be seen by the viewer.

Vertical Source Drives

Horizontal Gate Drives

The LCD Panel Assembly consists of (x4) major components.

1. Control PWB – inputs LVDS signal from the TV’s Video PWBs and outputs Drive Signals to the LCD Panel.

2. LCD Panel – Horizontal Gate and Vertical Source Drives on the LCD Panel create the displayed video image. Failures of these drivers will result in the Vertical and Horizontal line and Bar failures that are often seen with LCD TV’s.

3. Inverter PWBs – These convert the low voltage DC to High Output AC to power the Backlights. LCD Panel Assemblies may have (x1) or (x2) Inverter PWBs. Failure of (x1) Inverter PWB may result in partial or complete failure of the backlights.

4. Backlight – Provides light and allows the LCD Panel image to be seen by theviewer.

Metal Frame

LCD Panel

Drive PWBs

Diffusion Material

Backlight HousingBacklight THE LCD PANEL

This slide depicts the components of the LCD Panel to show their construction.

Removal of the metal frame of the LCD allows easy removal of the LCD Panel (LCD Cell and Drive PWBs).

These signals may run directly to the Inverter PWB in some cases

Control PWB

DC input Voltage may

vary

Inverter Board

To light the backlight, input DC from the TV Power Supply is stepped up to a High Voltage AC(AC950V for example).

The Backlight Control Signals may be processed at the Control PWB in some cases.

In other cases, these signals flow directly from the TV’s Digital Signal PWB to the Inverter.

THE LCD PANELLCD PANEL PWB FUNCTIONS

Control PWB (may be referred to as Main PWB)

The input digital video signal is memorized into the Frame Memory. The voltage for driving the LCD panel Drive Transistors is created from the data read out of the Frame Memory. This voltage is transferred to Gate-ICs in the panel. The LCD Panels Video lines are driven by the gate-ICs.

TV Power supply

The LCD Panel usually includes two electronic boards. The Control Board and the Inverter Board.

The Control Board’s primary function is to provide the data that drives the LCD panel’s Gate-ICs. The inputted LVDS signal from the TV’s Video Circuits’ is converted and read into the Frame Memory of the Control Board. The data that drives the LCD panel transistors is read from the frame memory and transferred to the Gate-IC in the LCD Panel. These Gate ICs drive the video lines of the LCD Panel.

The Inverter Board converts the small DC voltage from the TV power supply to the High Voltage AC that is required to power the LCD Panels backlight.

Backlight Control signal are used to control the ON/OFF and brightness of the backlight…This signal is usually created on the TVs Digital Signal Board and passes to the Inverter. In some instances, the signal passes to the LCD Panel Control Board prior to reaching the inverter.

Digital Signal PWB

BLOCK DIAGRAMSLCD Panel

Control PWB (LCD Panel)

Power Supply PWB

Master Inverter PWB

Analog PWB

LCD Panel

DC to DC PWB

CN00Q CN00P

T9501

CN

00A

CN

00B

LCD Power

LB_Power

24VDC

24VDC IC96025VDC

CN

10A

CN0DC

CN00HCN0DC

CN00H

CN0LV1

5/12VDC

IC6001

CN001

CN00W

PWM_DIM

DC_DIM

BL_ON

IC7033

24VDC

24VDC

Backlight

Backlight

CN

001

B1_Power

LCD Power

Slave Inverter PWB

(x20) total Backlights24VDC

5/12VDC

Based on LT-37X787/Z

Here we show the Signal flow from the TV’s PWBs to the LCD Panels Circuit Boards.

This Signal and Power flow may vary between TVs and LCD panels, but the general signals utilized will always be the same.

When troubleshooting Backlight problems, always trace the Backlight Control Signal Path from Board to Board to ensure the signal is being passed from the Source to the Intended Point.

Some LCD TVs will utilize a Master/Slave combination of Inverter Boards to power the LCD Panel Backlight. The Master Inverter may power half or the majority of the LCD Panel Lampswhile the Slave Inverter will power the remaining Lamps that are not powered by the Master.

Failure of either Master or Slave Inverter may result in total (in the case of a Master Inverter) or Partial (in the case of a Slave Inverter) Backlight loss depending on the actual failure.

Always ensure the supply voltages are present for the LCD Panel Control PWB and Inverter PWBs.

In some cases, the Inverter PWBs are controlled by the LCD Panel Control PWB. If this is the case, loss of LVDS signal to the Control PWB may result in a “NO Backlight” condition.

Always ensure the LVDS signal is present and the Supply Voltages to the TVs Video Processing ICs are correct. Failure or temporary fluctuations of the signal or voltages may result in Vertical Line failures or Video Image Freeze.

Block DiagramsExamples of Signal Flow to the Panel

Digital Signal PWB

Slave Inverter PWB(LCD Panel)

Control PWB (LCD Panel)

Power Supply PWB

Inverter PWB (LCD Panel)

Power Supply PWB

Inverter PWB (LCD Panel)

Control PWB (LCD Panel)

PWM_DIM

BL_ON/OFF

ANA_DIM

LVDS signal

Inverter DC voltage from Power Supply

DC from Power Supply

Example 1

Example 2

Backlight Control Signals

Panel

Backlight

Digital Signal PWB

Backlight

Panel

Here we show Examples of the Signal flow from the TV’s Digital Signal Board and the TV’s Power Supply to the LCD Panels Circuit Boards.

As you can see; while both examples use the same general Power, Video and Backlight Control Signals; there are (2) general variations of the Signal path.

Example 1 shows all the Backlight Control Signals passing through the Control Board to the Inverter Board.

In Example 2, the Backlight Control Signals are passed from the Digital Signal Board to the Inverter Board.

This block diagrams only shows the originating source of the signal. It is possible that the signals may pass directly through other PWBs . This is important because connector problems between PWBs may result in loss of 1 or more of these signals.

When troubleshooting Backlight problems, always trace the Backlight Control Signals Path from Board to Board to ensure the signal is being passed from the Source.. to the Intended Point.

Some LCD TVs will utilize a Master/Slave combination of Inverter Boards to power the LCD Panel Backlight. The Master Inverter may power half or the majority of the LCD Panel Lamps while the Slave Inverter will power the remaining Lamps that are not powered by the Master. Failure of either Master or Slave Inverter may result in total (in the case of a Master Inverter) or Partial (in the case of a Slave Inverter) Backlight loss depending on the actual failure.

Block DiagramsLVDS SIGNAL

8bit TTL RGB signal is converted to LVDS

LVDS is a differential signalTTL Signal is converted to

LVDS for transfer from the TVs Video PWBs to the LCD Panels Control PWB

TTL to LVD

S

LVD

S to TTL

PLL

PLL 100

ohm

100ohm

100ohm

100ohm

100ohm

TV Video Process IC

TV Video PWB

R0-R7

G0-G7

B0-B7

Data Enable

R0+

R0-R1+

R1-R2+

R2-R3+

R3-CLK+

CLK-

LCD Panel Video

Process IC

LCD Panel Control PWB

R0+

R0-

RGB signals are 8bit TTL signal.The chart below shows how a color would be represented by the data. For

example, a white raster is displayed by outputting all High data.Data Enable signals when information is ready to be displayed.LVDS is a differential signal. Two differential signals are sent by the LVDS transmitter and compared at

the receiver.TTL Signal is converted to LVDS for transfer from the TVs Video PWBs to the

LCD Panels Control PWB.TTL signals are limited to about 250MHz due to noise. LVDS is capable of up

to 1GBps.LVDS uses a lower voltage swing of 350mV, compared to TTL’s 3V, to allow

faster clocking.Differential signal eliminates noise problems of TTL making LVDS better for

signal transfer between TV and LCD Panel.

LVDS SIGNALSignal Breakdown

DE – Data Enable Signal

TV – Total Vertical Display time

TVD – Active Vertical Display Period

TVB – Vertical Blanking Period

TH – Total Horizontal Display time

THD – Active Horizontal Display Period

TC – Clock

TCH – clock high

TCL – clock low

TDS – data store timeTDH – data hold timeTES – enable store

This is a breakdown of the LVDS signal

DE – Data Enable Signal: signals when data is to be stored to pixel

TV – Total Vertical Display time: Timing of the Vertical signal information for Panel

TVD – Active Vertical Display Period: period that Vertical information is displayed on the LCD Panel

TVB – Vertical Blanking Period: timing of blanking pulse for pixels

TH – Total Horizontal Display time: timing of Horizontal signal information for panel

THD – Active Horizontal Display Period: period that the horizontal information is displayed on the LCD Panel

TC – Clock: timing signal for LVDS pixel data

TCH – clock high: clocks high swing

TCL – clock low: clocks low swing

TDS – data store time: time needed to store data to pixelTDH – data hold time: hold time for pixel dataTES – enable store: enable signal for storage of data to pixel

Control PWB TroubleshootingProblems1. No schematics given2. Failure symptoms similar to LCD Panel and Digital PWB failure. (difficult

to diagnose to specific problem with Control PWB)

Solution1. Check LVDS Input to Control PWB2. Check DC Power supply to Control PWB3. Visually/Electrically check major components4. Use symptom to diagnose problem

Control PWB Failure Causes1. Damaged PWB2. Circuit Failure on Control PWB3. NG inputs (video/dc) from TV PWBs

Troubleshooting the Control PWB is difficult due to the lack of schematics, the PWBs location, etc...

To adjust for these, new methods must be used to determine faults of the PWB and close attention must be paid to the specific symptoms of the failure.

Use the tips here to help determine Control PWB failures.

No video failures must be classified to help determine what caused the failure.1. No video, but the OSD and Backlight shows2. No Video, but Audio is OK3. No Video…at power ON, but after 13 seconds there is a picture4. No video….after 15 minutes.

Often times this information is requested from customers during the initial service contact, but the details are missed. Further information can help asses the failure prior to seeing the malfunction.

This is not a panel failure and may just be customer mistake…wrong input etc... There could also be a failure of the specific input being used since OSD added just before output to the panel. Trying a different input may help determine this problem.

1. No video with audio is a good sign of a panel problem. This could result from Inverter, Control PWB or Backlight failure. 85% of cases would be a failure of the Inverter or supply voltage to the inverter PWB. Knowing this helps determine the time and problems they may be experienced if attempting a fast TAT repair at the customer’s home

2. If the picture appears after a short delay, this may be a normal function of the TV. Many JVC TV have a short 13sec blanking period at power ON prior to the image appearing. Ask further questions to determine if this is the case. It is common for Technicians to forget to determine normal TV operation and Failure operation and spend hours troubleshooting a problem that doesn’t exist

3. No Video after a long period requires more information. Is the backlight ON…Did the TV shut Down…Are the LED’s flashing. Details in this case will prevent you from chasing the wrong problem.

Remember, detail is key when troubleshooting LCD TV and Panel failures. If you have the details, it makes it possible to determine a failure with the use of the information, block diagrams and flowcharts provided on the iSeeDatabase.

Check the DC voltage to the Control PWB

This is normally 9VDC to 12VDC

This voltage is required to power the Control PWBs circuits and ICs

In this case, the voltage has several inputs to the Control PWB

Connections and voltages will vary between LCD panels

Control PWB TroubleshootingCheck DC Power supply to Control PWB 1/2

Example from LT-42X478/V Schematic YA512

The control PWB requires a DC voltage (normally 9VDC to 12VDC) to power the Control PWBs circuits and ICs.

During troubleshooting of Video Problems related to the LCD Panel, ensure that you check that this voltage is present.

It will be necessary to check this voltage at the output of the TV’s PWB supplying voltage to the Control PWB since measurement on the Control PWB would be difficult due to its location.

If the voltage is missing at the TV side, try disconnecting the LVDS cable and rechecking the voltage. A shorted panel or Control PWB may cause the TV to Shut Down or the Voltage Supply to become shorted.

NG PWBControl PWB has

short of 12V supply

OK PWB

Control PWB TroubleshootingCheck DC Power supply to Control PWB 2/2

Measure from “VIN_12V” test point to PWB Ground to test 12V Circuit on PWB

Test point Location, Markings and Results will vary between LCD Panels

The control PWB requires a DC voltage (normally 9VDC to 12VDC) to power the Control PWBs circuits and ICs.

This is a simple check to determine if the supply on the Control PWB has been shorted.

A shorted Control PWB may cause the TV to shutdown due to an over-current condition.

Disconnecting the LVDS cable may allow the TV to Power ON in these cases.

If Disconnecting the LVDS cable allows TV Power ON, use this check to determine if the Supply on the Control PWB has been shorted.

A shorted LCD Panel may cause a similar Shut Down condition in the TV.

1. Input a White Raster using a Video Signal Generator

2. Check the LVDS signals

a. Positive and Negative pins will be inverse signals of each other. For instance; 2+ will be an inverse of 2-.

3. Change to Black Raster and look for change from high to low

4. Only 2+ and 2- are shown in the example, but all should be checked.

5. Marking of these signal will vary

NOTE:

Cold Solder or poor connections at this connector may result in Solarization Problems.

JVC

Example from LT-42X478/V Schematic YA512

Control PWB TroubleshootingCheck LVDS Input to Control PWB 1/3

Black Raster

2- with white Raster input

JVC

White Raster

2+ and 2- signal

2- with black Raster input

2+ with white Raster input

2+ with black Raster input

This schematic shows the partial section of the LVDS connection.

The signal will appear to be similar to the RF waveform of a VCR, with the incoming video signal being modulated by that carrier.

Positive and Negative pins will appear to be approximate inversesignals of each other. For instance; TA2+ will be an inverse of TA2-.

This signal may be checked by using an Oscilloscope to monitor the signal for change. Keep in mind that this is a high frequency signal that is difficulty to monitor during the test.

Perform the below to check the signal:

1. Input a White Raster using a Video Signal Generator 2. Check the LVDS signals 3. Input a Black Raster and you should notice video change

from a High to low signal on the modulated carrier4. Inverse signal should be seen when comparing + and -

RXINP0(Recive in Positive 0)

The LVDS signal consists of (x2) inverse signals, a Negative and Positive signal.

The test point should always have the same impedance measurement at both the negative and positive input for the signal.

This may be the same measurement for all LVDS signal inputs on the PWB.

The test point should always have the same impedance measurement at both the negative and positive input

Control PWB TroubleshootingCheck LVDS Input to Control PWB 2/3

RXINN0(Recive in Negative 0)

The LVDS signal consists of (x2) inverse signals, a Negative and Positive signal.

The test point should always have the same impedance measurement at both the negative and positive input for the signal.

This should be the same measurement for all LVDS signal inputs on the PWB.

RX0P(Recive in Positive 0)

Similar to previous PWB discussed in the previous slide, look for the LVDS test points on the PWB and compare measurements.

They should be approximately the same for all inputs on the PWB.

Control PWB TroubleshootingCheck LVDS Input to Control PWB 3/3

The test point should always have the same impedance measurement at both the negative and positive input

RX0N(Recive in Negative 0)

Similar to previous example, look for the LVDS test points on the PWB and compare measurements.

They should be approximately the same for all inputs on the PWB.

Look for obvious signs of damage to the Control PWB.

Check Fuses on the Control PWB.

Many of the Input and Output circuits are similar. Compare similar items looking for defect. For example, the LVDS input to Control PWB or Drive Outputs from the Control PWB to the LCD panel.

Control PWB TroubleshootingVisually/Electrically check major components

Troubleshooting the Control PWB is difficult due to the lack of schematics.

Use the tips here to help determine Control PWB failures.

Inverter TroubleshootingInverter failures1. Blown fuse – measure for open2. Circuit failure – visually inspect but difficult to

detect. Check for input signals to determine if the PWB should be operating

3. Transformer failurea. Shorted – cannot distinguish since shorted

and normal Output may have same impedance measurement. Require HV test to determine

b. OPEN – measure the output/input and compare Transformers to others on the PWB

4. Connection failure a. Loose/missing/cut

5. Damaged PWBa. Visually inspect PWB for this damage.

Troubleshooting the Inverter PWB is difficult due to the lack of schematics.

Use the tips here to help determine Inverter PWB failures.

The BL_ON, PWM_DIM and ANA_DIM signals should be present for backlight function

On the example shown, “ANA_DIM” is renamed “DC_DIM” at CN00W

The Inverters require DC from the Power Supply to operate.The Inverters DC Supply Voltage from the TVs Power Supply will

vary between LCD Panels and TV Models.Missing LVDS signal may also result in “No Backlight” defect

Examples are taken from LT-32X787

Schematic YA428

Inverters DC Supply Voltage from TV Power Supply

2-40(No.YA428)

Inverter TroubleshootingBacklight Signals

Here we show examples of the Backlight Power Supply and Backlight Control Signals. These examples were take from the Schematic for the LT-32X787.

There are (3) signals that MAY be used to control the Backlight. These are shown in the images located on the left of the screen.

“B” “L” ON or Backlight ON. This is a HIGH/LOW signal that signals the Backlight to turn ON or OFF.

“A” “N” “A” Dim or Analog Dim. This may also be referred to as “D” “C” Dim. This signal may be used to control the brightness of the Backlight. The Individual Inverter Ballast output current will be directly controlled by this input signals DC. A Higher DC Input.. will result in Higher output and Brighter Backlight. On the other hand, a lower DC input.. will result in a lower output and a Dimmer Backlight.

“P” “W” “M” Dim or Pulse Width Modulation Dim. This is a modulated signal that may be used to control the brightness of the Backlight. In this case.. the Inverter Output current is fixed, but the duty cycle of the PWM signal determines the OFF/ON period of the Inverter. A longer duty cycle will result in a brighter backlight, while a shorter duty cycle will result in a dimmer backlight.

Keep in mind that the naming of these signals may vary with the various TV models. Also, the signal name may change throughout the schematic. It may be best to follow these signals from the Inverter Board back to the TV’s Microprocessor during troubleshooting. Ensure that the signals are present at both location. Also keep in mind that some TVs will not utilizeall the Backlight Control Signals.

In the image on the Left Side.. you will notice the schematic showing the Inverter Board’s DC voltage Supply from the TV Power Supply. Always check these voltages when troubleshooting backlight problems to ensure they are present and stable. This DC voltage will vary based on TV Model and Panel Size.

Be aware that a missing LVDS Signal can result in the loss of the LCD Panel Backlight. This will result in both loss of Video and Backlight. Ensure that the LVDS signal is present to ensure that this is not the issue.

Inverter TroubleshootingPWB layout

Inverter PWBs consist of a Control Circuits and Power Circuits.

The Control Circuits provide voltage regulation, Power ON/OFF and Feedback.

There are generally multiple Power Circuits.

The Power Circuits are usually split into (x2) identical sectionon the PWB.

You can use these similarities to test for component malfunctions on the PWB by taking Measurements from the PWB Ground.

Many Inverter PWBs provide test points locations on the PWB that make these tests convenient.

Inverter has (x2) mirrored circuits

Inverter PWBs consist of a Control Circuits and Power Circuits.

The Control Circuits provide voltage regulation, Power ON/OFF and Feedback.

There are generally multiple Power Circuits on the Inverter PWB. Each Circuit is identical in design and function.

The Power Circuits are usually split into (x2) identical section on the PWB.

You can use these similarities to test for component malfunctions on the PWB by taking Measurements from the PWB Ground.

Many Inverter PWBs provide test points locations on the PWB that make these tests convenient.

Lamp output from the inverters ballast circuits share identical circuit designs.

Use the other circuits to help diagnose Lamp Output Circuit faults on the Inverter PWB.

Output Impedance to the lamp will measure the same at the test points located by the Lamp Connectors.

This will detect OPEN Transformer.

Shorted Transformer will not show by this method normally.

Inverter TroubleshootingBallast Circuit Check 1/2

Measurements are Approximately the same, so outputs are assumed OK.

Compare to remaining circuits on PWB to determine the normal output measurement

Lamp output from the inverters ballast circuits share identical circuit designs.

Use the other circuits to help diagnose Lamp Output Circuit faults on the Inverter PWB.

Output Impedance to the lamp will measure the same at the test points located by the Lamp Connectors.

This will detect OPEN Transformer.

Shorted Transformer will not show by this method normally.

NG Circuit

The NG circuit measured at 5.03K.

All others measured at approx 5.3K ohm.

Large differences may be a sign of Circuit failure.

In this cause, the failure resulted in a “NO Backlight”condition.

The Inverter PWBs consists of Control Circuits that will Shut OFF the Backlight if failures are detected.

Backlight Shutoff due to the Inverters Failure detection will usually occur within 3 seconds of the Backlight showing. This will not cause the TVs LEDs to flash unless the failure is also detected by the TVs PWBs.

OK Circuit

Inverter TroubleshootingBallast Circuit Check 2/2

The NG circuit measured at 5.03K, All others measured at approx 5.3K ohm.

Large differences may be a sign of Circuit failure, In this cause, the failure resulted in a “NO Backlight”condition.

This Inverter PWBs control circuits usually sense these differences or failures.

The Inverter PWBs consists of Control Circuits that will Shut OFF the Backlight if failures are detected.

Backlight Shutoff due to the Inverters Failure detection will usually occur within 3 seconds of the Backlight showing. This will not cause the TVs LEDs to flash unless the failure is also detected by the TVs PWBs.

BACKLIGHT TROUBLESHOOTING 2/3

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.

Another 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.

This will, in effect substitute, 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.

A very large flashlight had to be used to take the pictures shown above.

If the Inverter fails or the Backlight Bulbs do not ignite, the video signal may still be present. If this is the case, it may be possible to see the TV video with a large flashlight. By Shining a Large flashlight at an angle toward the screen; some of the video may become visible. The presence of Video without the Backlight is a clear sign of an Inverter problem. Further troubleshooting of the Backlight DC supply and Backlight Signals is necessary to determine if the Inverter requires replacement.

Keep in mind, a very bright flashlight is required for the test to effectively work. Additionally, the video is difficult to see under these conditions. Therefore look closely and double-check your results.

This Test will only be useful if the LCD Panel and TV Video Circuits are fully functioning. Certain other LCD Panel and TV Video Circuit failures may also result in Backlight malfunction.

A Voltage tester may be used to test the individual Lamp Outputs from the Inverter PWB.

This will help access if a Bulb in the panel is blown or if the Inverter has no output to the Bulb.

1. With the TV Power OFF, disconnect Bulb to allow insertion of the Tester.2. Insert Tester to allow testing of the output.3. Turn ON TV power.4. The Light, on the Tester, will flash to show “Good” output from the inverter.

The Inverter tests for load upon TV Power ON. If no load is present, it will not provide an output. If the tester is connected after TV Power ON, the test will always fail.

Standard Voltage Tester used for testing AC Line

1

2

4

Inverter TroubleshootingInverter Output test

This is a simple test for checking the output from the Inverter to the Backlight.

The Inverter Board uses individual Ballast circuits to power the LCD Panel Backlights. It is possible to test these individual outputs by using a Simple AC line Voltage Tester.

While the TV Power is OFF. Disconnect the Lamp output from the Inverter Board.

Insert the Test Probe into the connector on the Inverter Board, Polarity is not important.

When you Turn ON the TV Power, Watch for the Test Probe to signal the circuits. function.

The tester should flash ON, Then OFF if the output is functioning. A Good Test will signify that the output to that Lamp is working only.

It is important to remember that some Inverter Boards will look for a load upon Power UP. If a load is not present, the Inverter will shut off. While attempting this test, ensure that the Test Probe is connected prior to powering ON the TV. If this is not done the Inverter Board will shut down before your are able to check the output.

THE LCD PANELThe Back Light/Diffuser

Inverter/Ballast Circuit

Single Fluorescent Lamp

BACKLIGHT

The Backlight is made up of many small thin Fluorescent Tubes.(1)

Each individual fluorescent tube has its own ballast or inverter circuit.(2)

This Backlight provides the Light Source for the LCD Panel Image.

Without the Backlight, The Image may be created by the LCD panel, but will not normally be viewable.

DIFFUSER

The diffuser is made up of multiple layers of material. (3)

This material ensures that there is an even dispersion of light on the panel. (no bright spots)

Each Fluorescent Lamp has its own Ballast or Inverter circuit

LCD Panel with LCD layer removed

LCD Panel with LCD layer and Diffuser removed

Rear View LCD Panel

Multiple Layers of Diffusion Material3

2

1

BACKLIGHT

The Backlight is made up of many small thin Fluorescent Tubes.(1)

Each individual fluorescent tube has its own ballast or inverter circuit. (2)

This Backlight provides the Light Source for the LCD Panel Image.

Without the Backlight, the Image may be created by the LCD panel, but will not normally be viewable.

DIFFUSER

The diffuser is made up of multiple layers of material. (3)

Multiple layers of diffusion material are used to create an evenly illuminatedpicture.

This material ensures that there is an even dispersion of light on the panel. (no bright spots)

LCD Panel Inverter Defect

Control PWB Defect

Check TV Power Supply

OK NG

OKCheck “PWM_Dim”signal to Inverter (4)

OKNGNG

NG NA

Not a Panel DefectCheck TV PWBs,

connections and wires

OK

Start NA Means Signal path does not go through Control PWB

Check “ANA_Dim”signal to Inverter (4)

NG

Check “Backlight On” signal to

Inverter (4)

OK

TROUBLESHOOTING FLOWCHART

Display or image defect

Check defect against Panel Specification

NO

NO

Check LVDS signal, cable and connections (3)

OKNG

Lines in Display

NG

NO

OK NG

Not a Panel DefectCheck TV PWBs,

connections and wires

Missing Pixels

YES

Backlight defect (1)

YES

YES

YES

NO

OK

YESNot a Panel DefectCheck TV PWBs,

connections and wires

NO

Not a Panel DefectCheck TV PWBs,

connections and wires

Check this Signal into the Control PWB

Check LVDS signal, cable and connections (3)

Check for Panel or Control PWB Defect

Check “On Screen Menu”

Check DC Voltage to Inverter from Power SupplyImages seen using flashlight (2)

REFERENCE NOTES

(1) Check for appearance of Backlight through LCD Panel frame, as this may not be visible from front of TV.

(2) Refer to “Backlight Troubleshooting” section

(3) Refer to “LVDS Signal “Section

(4) Refer to “LCD Panel PWB” function section

Follow this flowchart to assist with the diagnosis of LCD Panel failures.

Use the supplied troubleshooting steps from this guide and commonly practiced troubleshooting steps to eliminate potential causes of the failure.

When troubleshooting NO VIDEO problems.. always look for the presence of a backlight before proceeding. The Backlight may be difficult to see under normal conditions, so it may be necessary to look for this on the sides of the LCD Panel frame.

Abnormal picture on half screen

Vertical or horizontal lines

Wavy color shading

Noise

White Display

EXAMPLES Control PWB failures

No Display

The Control PWB only causes this defect when the Backlight Control Signals are Output from the Control PWB

No LVDS signal may also result in this symptom

Other failures may present with similar symptoms

Here we show examples of defects that may be caused by the Control Board of the LCD Panel. If it is decided that the Control Board is faulty through troubleshooting, refer to the Service Manual for the Part Number of the part required.

Many of these Error may reflect errors that may be caused by the TV’s Video Circuits. Display the TV’s User menu to eliminate SOME of those TV Circuit Failures. When the failure does not show in the TV’s User Menu, the error cannot be the LCD Panel or its Boards. If the error shows in the TV’s User Menu, further troubleshooting is required to determine the appropriate source.

Abnormal Display On Half of the Screen is caused when the Control Board is unable to properly address a portion of the screen.. resulting in No Video Output in that area of LCD Panel.

No Display conditions may occur under several circumstances. This symptom may occur with or without the presence of a backlight since the backlight signals are often passed from the Control Board to the inverter.

White Display, Noise in the Video and Wavy Color Shading can all result from an improper video output from the Control Board. This will occur when the Control Board does not properly bias the drive ICs of the panel causing this video error to occur.

EXAMPLES LCD Panel Defects

Vertical or Horizontal lineColor Shading (like a band)Some gate-ICs are not operating correctly.

Bright dot / Black dotBright dot – always ON Black dot –always OFF. 1) It varies depending on input signal.2) Observe it with magnifying glass 3) Check against Specification:(For details, please refer to the service policy.)

Partial No DisplayGate-ICs drive the horizontal lines. If a gate-IC is broken, other gate-ICs below it will not be driven as well.

No video below this area

Other failures may present with similar symptoms

Here we show examples of defects that may be caused by the LCD Panel. If it is decided that the Panel is faulty through troubleshooting, refer to the Service Manual for the Part Number of the part required.

The Errors shown here Partial NO Display.. Color Shading.. and Vertical or Horizontal Line may all be caused by a failure of the Drive ICs within the LCD Panel. These Drive ICs bias the Pixels of the display turning them ON or OFF. In the Case of Partial NO Display shown, since gate ICs are driven in Groups, the failure of a single IC will result in no operation of the ICs below it in the group.

A Bright Dot defect results when a pixel is always on. This is tested using a Black or dark Video pattern. A Dark dot defect results when a pixel will not turn ON. This is tested using a white pattern. In both instances it is necessary to check the defect against the specification of the TV Model and LCD Panel. This defect is easily seen when using a Magnifying Glass to view the pixel. By doing so, you will be able to judge the Pixel’s color, size, and shape if needed.

EXAMPLES Inverter Defects

No Display Partially Dark(dark band in image)

See also “LCD Panel Defect Examples”

Some Panels use (2) Inverter Boards, Master and Slave. For thesemodels Confirm the symptom and check the corresponding PWB.

If the voltage for the Backlight is not supplied, luminance-shading could occur. This is difficult to identify with a normal picture. Therefore, when you check this, input an all-white picture to confirm the phenomenon.

Other failures may present with similar symptoms

Here we show examples of defects that may be caused by the LCD Panel’s Inverter or Inverters. If it is decided that the Inverter is faulty through troubleshooting, refer to the Service Manual for the Part Number of the part required.

No Display conditions will result when the Backlight is not operating. This may be caused by both an inverter or backlight failure. In these cases, the TV Audio may be heard and the LCD Panel may still display video, but this video will not be easily seen since the Backlight is not operating. Use the previously discussed troubleshooting methods to assist in the diagnosis of this failure.

Partially Dark image may be the result of one of the Inverters not functioning at peak capacity due to low input voltage or failure. Since these errors are difficult to see.. input a 100% all white video signal to aid with the diagnosis. This may also be caused by a faulty backlight.

Some failures may not show with 100% video input.. So it is often wise to lower this input signal to about 25-30% to insure that the Backlight remains evenly spread over the panel under all circumstances.

EXAMPLES Backlight/Diffuser defects

Partially dark color Dark LinesSee also “Inverter Defect Examples”

This may be caused by damaged or shifted diffuser

Other failures may present with similar symptoms

No Display Partially dark(dark band in image)

See also “LCD Panel Defect Examples”Some backlights may not be functioning

Dark Lines and Partially Dark Color, may result if there is a defect in the diffusion material used to evenly spread the light produced by the LCD Panel’s Backlight. Since the light is not even in an area, that area will appear darkened. This is easily visible with bright white video.

No Display conditions will result when the Backlight is not operating. This may be caused by both an inverter or backlight failure. In these cases, the TV Audio may be heard and the LCD Panel may still display video, but this video will not be easily seen since the Backlight is not operating. Use the previously discussed troubleshooting methods to assist in the diagnosis of this failure.

Partially Dark image may be the result of one of the Inverters not functioning at peak capacity due to low input voltage or failure. Since these errors are difficult to see.. input a 100% all white video signal to aid with the diagnosis. This may also be caused by a faulty backlight.

Some failures may not show with 100% video input.. So it is often wise to lower this input signal to about 25-30% to insure that the Backlight remains evenly spread over the panel under all circumstances.