Jvc Lcd Service Traninig

L CD P a n e l Service Training

2008

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

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

1. Serv Servic ice e Info Inform rmat atio ion n

6. Inve Invert rter er PWB PWB Tro Troub uble lesh shoo ooti ting ng

2. The LCD Panel

7. Back acklig light/D ht/Dif iffu fus ser

3. Block Diagrams

8. Flowchart

4. Co Cont ntro roll PWB PWB Trou Troubl bles esho hoot otin ing g 9. Examples

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

SERVICE INFORMATION Model Identification

LT-32E488 Version “VA

LT-32E488 Version “SAA”

Different Version Identified Here



Prior to service, it is always wise to verify the Model and Version to en 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 There are other differences between the models that were not explain



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



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



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

THE LCD PANEL Components of The LCD Panel Control PWB

LCD Panel

Inverter(s)

(Cell and Drive PWBs)

The LCD Panel Assembly c (x4) major components.

Vertical Source Drives

1. Control PWB – inputs LVDS s TV’s Video PWBs and outputs the LCD Panel

2. LCD Panel – Horizontal Gate a Source Drives on the LCD Panel displayed video image

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

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

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

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

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

Backlight Housing

Backlight

THE LCD PANE

Drive PWBs

LCD Panel

Diffusion M

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).

THE LCD PANEL LCD 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.

Control PWB

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

DC input Voltage may vary

Inverter Board

The

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

The

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

The

Inverter Board converts the small DC voltage from the TV power sup 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

BLOCK DIAGRAMS LCD Panel 24VDC

DC to DC PWB

Power Supply PWB

 C  N   0   0  B 

LCD Power LB_Power

Control PWB (LCD Panel)

T9501  C  N   0   0  A 

24VDC

 C  N  1   0  A 

24VDC

IC9602

Master Inverter PWB

5VDC CN00Q 24VDC

LCD Power

CN00P

CN00H

CN0DC

24VDC

Slave Inverter PWB Digital Signal PWB

Analog PWB

5/12VDC

IC6001

IC7033

B  L   _  O N 

CN00H

CN0DC

DC_DIM

B  1   _ P   o w  e r 

CN001

 C 



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



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



When troubleshooting Backlight problems, always trace the Backlight Control Signa Board to Board to ensure the signal is being passed from the Source to the Intende



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



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



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



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

Block Diagrams Examples of Signal Flow to the Panel Power Supply PWB

Digital Signal PWB

Control PWB (LCD Panel)

Inverter PWB (LCD Panel)

Example 1 Control PWB (LCD Panel)

Digital Signal PWB

Inverter PWB (LCD Panel)

P a n e l

B a c k l i g h t

P a n e l B a c

Here

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

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

1 shows all the Backlight Control Signals passing through the Control Boa Inverter Board. In

Example 2, the Backlight Control Signals are passed from the Digital Signal Boa Inverter Board. This

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

troubleshooting Backlight problems, always trace the Backlight Control Sign from Board to Board to ensure the signal is being passed from the Source.. to the In Point. Some

LCD TVs will utilize a Master/Slave combination of Inverter Boards to power

Block Diagrams LVDS SIGNAL R0-

R0+

TV Video Process IC

T  R0-R7 T  L  G0-G7  t    o B0-B7 L  V  D  Data Enable  S 

R0R1+ R1-

TV Video PWB

100 ohm

R2+ R2-

100 ohm

R3+ R3-

P  L  L 

100 ohm

 t    o T  T  L 

LCD Panel Video Process IC

R0+

100 ohm

CLK+ CLK-

L  V  D   S 

100 ohm

P  L  L 

LCD Panel Control PWB

8bit TTL RGB converted to LV  LVDS is a dif  TTL Signal is LVDS for transf Video PWBs to Control PWB 

RGB signals are 8bit TTL signal. below shows how a color would be represented by the data  The chart below 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 signals are sent by the LVDS LVDS transmitter and compa the receiver.  TTL Signal is converted to LVDS for transfer from the TVs Video PWB LCD Panels Control PWB.  TTL signals are limited to about 250MHz due to noise. LVDS is capa to 1GBps.  LVDS uses a lower voltage swing of 350mV, 350mV, compared to TTL’s 3V, t faster clocking.  Differential signal eliminates noise problems of TTL making LVDS be signal transfer between TV and LCD Panel. 

LVDS SIGNAL Signal Signal Break Breakdow down n DE  – Data Enable Enable Signal Signal TV – Total Vertical Vertical Displa Display y time TVD – Active Active Vertical Vertical Display Display Period Vertical Blanking Blanking Period Period TVB – Vertical

Total Horizontal Horizontal Display Display time TH – Total

THD – Active Horizontal Display Period Clock k TC – Cloc

TCH – clock clock high high TCL – clock clock low TDS – data store time



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 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 pixel TDH – data hold time: hold time for pixel data TES – enable store: enable signal for storage of data to pixel

Control PWB Troubleshootin Problems 1. No schematics given 2. Failure symptoms similar to LCD Panel and Digital PWB failure. to diagnose to specific problem with Control PWB)

Solution 1. Check LVDS Input to Control PWB 2. Check DC Power supply to Control PWB 3. Visually/Electrically check major components 4. Use symptom to diagnose problem Control PWB Failure Causes 1 Damaged PWB



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 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 shows 2. No Video, but Audio is OK 3. No Video…at power ON, but after 13 seconds there is a picture 4. No video….after 15 minutes.  Often times this information is requested from customers during the initial service contact, but the details 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 fa specific input being used since OSD added just before output to the panel. Trying a different input may help this problem. 1. No video with audio is a good sign of a panel problem. This could result from Inverter, Control P Backlight failure. 85% of cases would be a failure of the Inverter or supply voltage to the inverte Knowing this helps determine the time and problems they may be experienced if attempting a 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 short 13sec blanking period at power ON prior to the image appearing. Ask further questions to if this is the case. It is common for Technicians to forget to determine normal TV operation and 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 D the LED’s flashing. Details in this case will prevent you from chasing the wrong problem. 

Control PWB Troubleshooting Check DC Power supply to Control PWB 1/2

Example from LT-42X478/V Schematic YA512

Check the DC voltage to the Control PWB

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

During troubleshooting of Video Problems related to the LCD Panel, e 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 Contro would be difficult due to its location. 

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

Control PWB Troubleshooting Check DC Power supply to Control PWB 2/2 Measure from “VIN_12V” test point to PWB Ground to test 12V Circuit on PWB

NG PW

Control PWB short of 12V s

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

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

A shorted Control PWB may cause the TV to shutdown due to an overcurrent 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 t determine if the Supply on the Control PWB has been shorted. 

Control PWB Troubleshooting Check LVDS Input to Control PWB 1/3 2+ and 2- signal

White Raster

Black Raster

JVC

JVC

Example from LT-42X478/V Schematic YA512 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

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 inverse signals of each other. For instance; TA2+ will be an inverse of TA



This signal may be checked by using an Oscilloscope to monitor th signal for change. Keep in mind that this is a high frequency signa 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

Control PWB Troubleshooting Check LVDS Input to Control PWB 2/3 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

RXINN

(Recive in Neg

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 th signal. This

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

Control PWB Troubleshooting Check LVDS Input to Control PWB 3/3

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.

RX0N (Recive in Negative 0)

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

RX0P (Recive in Positive 0)

Similar

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

should be approximately the same for all inputs on the PW

Control PWB Troubleshooting Visually/Electrically check major components



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. 

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



Use the tips here to help determine Control PWB failures.

Inverter Troubleshooting Inverter failures 1. Blown fuse – measure for open 2. Circuit failure – visually inspect but difficult to detect. Check for input signals to determine if the PWB should be operating 3. Transformer failure a. b.

4.

Shorted – cannot distinguish since shorted and normal Output may have same impedance measurement. Require HV test to determine OPEN – measure the output/input and compare Transformers to others on the PWB

Connection failure a.

5.

Loose/missing/cut

Damaged PWB a

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.

Inverter Troubleshooting Backlight Signals Inverters DC Supply Voltage from TV Power Supply

2-40(No.YA428)

Examples are taken from LT-32X787 Schematic YA428



Here we show examples of the Backlight Power Supply and Backlight Control Signals. These examples we 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 t 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 con of the Backlight. The Individual Inverter Ballast output current will be directly controlled by this input signals D Input.. will result in Higher output and Brighter Backlight. On the other hand, a lower DC input.. will result in a 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 b Backlight. In this case.. the Inverter Output current is fixed, but the duty cycle of the PWM signal determines period of the Inverter. A longer duty cycle will result in a brighter backlight, while a shorter duty cycle will resu backlight.



Keep in mind that the naming of these signals may vary with the various TV models. Also, the signal name m throughout the schematic. It may be best to follow these signals from the Inverter Board back to the TV’s Mic during troubleshooting. Ensure that the signals are present at both location. Also keep in mind that some TV all the Backlight Control Signals.

Inverter Troubleshooting PWB 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 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.

Inverter has (x2) mirrored c

Inverter The

PWBs consist of a Control Circuits and Power Circuits.

Control Circuits provide voltage regulation, Power ON/OFF and Fee

There

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

Power Circuits are usually split into (x2) identical section on the PW

You

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

Inverter PWBs provide test points locations on the PWB that mak tests convenient.

Inverter Troubleshooting Ballast Circuit Check 1/2

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.

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.

Inverter Troubleshooting Ballast Circuit Check 2/2

The All

NG circuit measured at 5.03K.

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.

OK Circ



The NG circuit measured at 5.03K, All others measured at approx 5.



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



This Inverter PWBs control circuits usually sense these differences 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 o within 3 seconds of the Backlight showing. This will not cause the T 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. 



If the Inverter fails or the Backlight Bulbs do not ignite, the video signal may st 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 o video may become visible. The presence of Video without the Backlight is a cl sign of an Inverter problem. Further troubleshooting of the Backlight DC supp Backlight Signals is necessary to determine if the Inverter requires replaceme



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 loo 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

Inverter Troubleshooting Inverter Output test

2

1

4

Standard Voltage Tester used for testing AC Line



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.



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 li 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 circuit function.



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

LCD Panel with LCD layer removed

THE LCD PANEL The Back Light/Diffuser

3

Single Fluorescent Lamp

1

LCD Panel with LCD layer and Diffuser removed

Each Fluorescent Lamp h Ballast or Inverter c

BACKLIGHT

2

The

Backlight is made small thin Fluorescent T Each

individual fluoresc own ballast or inverter c This

Backlight provides Source for the LCD Pan Rear View LCD Panel

Without

the Backlight, T be created by the LCD p normally be viewable.

BACKLIGHT The

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

Each This

individual fluorescent tube has its own ballast or inverter circuit.

Backlight provides the Light Source for the LCD Panel Image.

Without

the Backlight, the Image may be created by the LCD panel, b 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 illum

picture. This

material ensures that there is an even dispersion of light on the p

YES

Backlight defect (1)

Start

NO

TROUBLESHOOTING FLOWCHART YES

Display or image defect

Images seen using flashlight

(2)

NO

Not a Panel Defect

NG

Check Power S

YES

Check TV PWBs, connections and wires

Check “On Screen Menu” OK

NG

Check “Backlight On” signal to Inverter (4)

OK

OK

Check “PWM_Dim” signal to Inverter (4)

Check “AN signal to In

NG

NG

Mean go t

Check DC Voltage to Inverter from Power Supply OK

NO

NA

NG

Check this Signal into the Control PWB YES

Lines in Display

NG

NO

Not a Panel Defect Check TV PWBs, connections and wires

Missing Pixels YES

NA

NO

Check LVDS signal, cable and connections (3)

OK

Check L and

Control PWB Defect LCD Panel Inverter Defect

OK



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 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 th LCD Panel frame.

EXAMPLES Control PWB failures

Other failures may present with similar symptoms

The

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

Abnormal picture on half screen

No

LVDS signal may also result in this symptom

No Display

White D



Here we show examples of defects that may be caused by the Control Board o Panel. If it is decided that the Control Board is faulty through troubleshooting, re 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 Ci Display the TV’s User menu to eliminate SOME of those TV Circuit Failures. W failure does not show in the TV’s User Menu, the error cannot be the LCD Pane Boards. If the error shows in the TV’s User Menu, further troubleshooting is req determine the appropriate source.



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



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



White Display, Noise in the Video and Wavy Color Shading can all result from a video output from the Control Board. This will occur when the Control Board do

EXAMPLES LCD Panel Defects

Other failures may present with similar symptoms

No video below this area

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

Bright dot / B

Bright dot – always O Black dot –always OF 1) It varies depending 2) Observe it with ma 3) Check against Spe (For details, please re policy.)



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



The Errors shown here Partial NO Display.. Color Shading.. and Vertical or Line may all be caused by a failure of the Drive ICs within the LCD Panel. Drive ICs bias the Pixels of the display turning them ON or OFF. In the Ca Partial NO Display shown, since gate ICs are driven in Groups, the failure of 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 dark Video pattern. A Dark dot defect results when a pixel will not turn ON. tested using a white pattern. In both instances it is necessary to check the d against the specification of the TV Model and LCD Panel. This defect is eas when using a Magnifying Glass to view the pixel. By doing so, you will be ab  judge the Pixel’s color, size, and shape if needed.

EXAMPLES Inverter Defects

Other failures may present with similar symptoms

No Display 

Partially Dark

(dark band in image) See also “LCD Panel Defect Exam

Some Panels use (2) Inverter Boards, Master and Slave. For these

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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.

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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.

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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.

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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 Other failures may present with similar symptoms

No Display

Partially dark color

Partially dark (dark band in image) See also “LCD Panel Defect Examples” Some backlights may not be functioning

Dark Lines See also “Inverter Defect Examples” This may be caused by damaged or shifted diffuser