Panasonic TX-L37G10E – Service mode access – Self check mode – LVDS connection details

Self Check
Self-check is used to automatically check the bus lines and hexadecimal code of the TV set. To enter Self-Check mode, keep pressing the down (-/v) button on the TV set and press the STATUS button on the remote control. To exit Self Check, switch off the TV set at the power button.

Power LED blinking and causes

When abnormality has occurred the unit, the protection circuit operates and reset to the stand by mode. At this time, the defective block can be identified by number of blinking of the Power LED on the front panel of the unit.

LED BLINKING AND CHECK POINTS 

Blinking times	Contents	Check point
1	INVERTER_SOS	A BOARD, P UNIT
2	FAN_SOS	A BOARD
3	SOS	A BOARD
4	SUB_F_12V	A BOARD P UNIT
5	MAIN_9V	A BOARD
6	SUB_5V	A BOARD V BOARD
7	SUB_3.3V	A BOARD
8	MAIN_3.3V	A BOARD V BOARD
9	SOUND_SOS	A BOARD
10	ZWEI_SOS	A BOARD
13	Emergency SOS	A BOARD
14	AUDIO_PWM_SOS	A BOARD

Service Mode Function
MPU controls the functions switching for each IICs through IIC bus in this chassis. The following setting and adjustment can be adjusted by remote control in Service Menu
How to enter SERVICE
While pressing (-/v) button on the TV unit, press on the remote control for 3 times within 2 seconds.
Note:
To exit from Service mode, press 0 the exit button on remote control.
Key Command
# Press the 3/4 button to change the adjustment values or function.
# Press the 1/2 button to step up/down through the functions and adjustments
# Press the numerical button VOLUME (+/-) to change of each option item.
# Press the OK button after each adjustment has been made to store the required values.

LVDS CONNECTION DETAILS  

Tech troubleshooting – TCON board – Backlight Dimming through TCON board – Deference between TCON and 3D TCON board - Purpose of LED in TCON board

T-CONs Deliver P-DIM (Dimming Signals) to the Inverter
P-DIM (Called PWM-DIM which stands for Pulse Width Modulation Dimming) is a signal from the Main board that is generated by monitoring the Video content’s average brightness level. It is then sent to theBacklight driver IC to control the brightness of the backlights accordingly. The maximum brightness level isestablished by the customer through the Customer’s Menu in the Video selection under Backlights. Thissetting has a bar graph that can be set from 100% down to 0%.
The P-DIM signal will follow the percentile setting proportionately. The range of P-DIM is 3.3V to 0V. Sowhen the bar graph is set for 100% the P-DIM line will be 3.3V and the backlight brightness will be maximum.
Most often the P-DIM line is routed directly from the Main board to the Power Supply, it is routed through thePower Supply directly to the Inverter and then to the Backlight driver IC.
(If the Power Supply has an on-board Inverter, the Driver IC is on the Power Supply itself). However,on some sets, the P-DIM line is routed to the T-CON board.The T-CON then generates a control signal that is then routed to the Inverter and then to the Driver IC.

Here is the T-CON from a 42SL80. The connector in the bottom left goes to the Inverter and carries the P-DIM Control Signals. The P-DIM signal from the Main board is brought in on pin 8 of the left LVDS and is then routed to the large MCM IC. Then it is output through the 8 pin IC on the bottom left to the connector.

Troubleshooting the P-DIM Line when Routed Through the T-CON

When troubleshooting this type of P-DIM routing, you will still use the same procedure. Enter the Customer’s Menu and go to Video, then select Backlights. Place a DC voltage meter on the output from the T-CON CN3or the input to the Inverter CN2. You can check either of the two pins. While adjusting the Backlights from 100% down to 0% the P-DIM lines will vary accordingly from 2.4V at 100% down to 0.67V at 0%.

Pin	Label	Run	Diode Test
1	n/c	n/c	n/c
2	SCAN 1	0.67V>2.4V	Open
3	SCAN 2	0.67V>2.4V	Open
4	Gnd	Gnd	Gnd

Function of the Blue LED on Some T-CON Boards

On some of the LCD T-CONs there is a bright Blue LED that turns on for a brief moment during turn on and then it shuts off. These are only used in set with Florescent Bulbs as the Backlights. As in the example below (from 42LG60), it shows the Blue LED is on the lower right hand side.
The purpose of LD1 is to help excite the Selenium gas in one of the backlight bulbs. This helps the bulb to light when there’s little room light by pre-exciting the gas. With little room light, the gas in the florescent Bulbs tends to lie dormant, (Little movement). This LED help to get the Electrons moving just before the point of firing (turning on).  There is a small hole under LD1. This is how the light goes through the board to get to the Bulbs. (There is a hole in the back metal cover of the panel as well).

Differences between a T-CON and a 3D FRC T-CON

The typical T-CON’s basic responsibilities are to drive the TFT panel and to generate panel voltages.The video input through the LVDS cables is already formatted for usage by the T-CON board.

Typical T-CON

The 3D FRC T-CON basic responsible to; generate panel voltages. When not in 3D it generates the Tru-Motion, Motion Estimated Motion Compensated (MEMC) frames. When in 3D it unpacks 3D frame content. It generates 3D sync which is used by the 3D Shutter glasses. It formats the video for usage by the panel driver circuit and it drives the panel. The video input through the LVDS cables is 24 bit LVDS video.

3D FRC T-CON

Since the 3D FRC T-CON does so much more work than a standard T-CON, it has an additional 12V input via a two wire connector. The voltage is from the same source as a typical TCON board. It comes from the  power supply and switched on/off by the Main board.

T-CON board Troubleshoot – No picture on LCD TV

Troubleshooting No Picture problem.
When dealing with a suspected T-CON problem, the very first thing you should approach is “Does the T-CON board have it’s operational voltage” TV TURN ON PROCESS: When the TV turns on, it is a 3 step process.

Step 1) RL-ON called (Relay On) or PWR ON _ON called (Power On). This turns on the power supply which turns on all the voltages that the Main board needs to operate. It also turns on the backlight B+ even though the backlights will not be ON at this time. The Main board needs several voltages to operate. It needs the Stand-By voltage which is always present even if the set is not turned on. It needs what is called Video Processing voltage which is 12V. And it needs Audio amplification voltage which can vary dependent upon the wattage output of the audio amplifier. This voltage will be either 17V or 24V. This voltage can also be used to generate Tuner voltage.
Step 2) Panel_CTL called (Panel Control). This will be the command that actually turns on the T-CON operational voltage by activating a switch that takes the 12V from the Power Supply and routes it to the T-CON board through the LVDS cable. 3D model T-CONs also have a secondary 12V supply (which comes from the same switch) and sends it to the T-CON through a two pin connector for additional current demands of the 3D T-CON. It is not the fact that the T-CON 12V current is too much for the 12V supply, it is that the current demand of the 3D FRC T-CON is too much for the thin wire in the LVDS cable.
Step 3) INV ON _ON called (Inverter On) or DRV ON _ON called (Drive On) This command will turn on the backlights .This output from the Main is sent back to the Power Supply to activate the backlight driver IC. If the backlights have an external Ballast (Inverter), the INV_ON line will be routed through the Power Supply to the Inverter. The same thing holds true for LED backlights which may have an internal or external Inverter.

So the area to concern when dealing with a No Picture symptom is to first make sure there are backlights . If the backlights do not comes on, you still may be able to see if the panel is working by using a flashlight and looking (at close proximity) to the panel. Hold the flashlight close to the panel and look carefully for any movement within the panel. You may also be able to shine the flash light through any hole in the metal shield covering the back of the panel. If you see movement, this would indicate there is activity in the LCD panel and that you need to investigate the problem from the backlight. Remember the backlights (Florescent or LED) need a power supply (24V) and the turn on command called DRV_ON or INV_ON.

Troubleshooting a No Picture problem, checking Power Supply voltages.
If you have backlights but you have no picture, the fist step is to check the connector from the Power Supply to the Main board. Confirm the 3 voltages, STBY voltage, 12V and 17V/24V. You can also listen for audio which would confirm that the Main board is processing audio and it has the Audio B+.

In the Turn On sequence, Panel_CTL turns on the 12V to the T-CON. Once you have confirmed that the Main board is receiving the correct voltages, you need to confirm that the T-CON is receiving its operational voltage. The best way to check is to begin with the LVDS cable from the Main to the T-CON. It will have a test point for the 12V to the T-CON. Look on the left or right side for 4 pins tied together, this will be the 12V test point. In some cases when the set has two LVDS cables, look on the LVDS cable with the most pins (usually 51). (The LVDS cable with the fewer pins will not be carrying any DC voltage).
Tip: Some models use the first and last pin as ground. This is easy to verify with a DVM in ohms.

12V TO THE T-CON:
Here is an example of how the T-CON 12V is routed to the LVDS connector. You will note that pins 48 through 51 are carrying the 12V to the T-CON. In this case it is not possible visually to determine on the PCB that the last 4 pins are tied together. This is where you would measure the 2nd and the next to the last pin for 12V.

In the Turn On sequence, Panel_CTL turns on the 12V to the T-CON, look at the circuit shown in the example below.

Here is an example of how the T-CON 12V is switched on/off on the Main board. When the Microprocessor outputs Panel_CTL it is routed to Q505 which turns on. The Collector current goes high and the collector voltage goes low. This drops the base of Q506 low and Q506 turns off. This allows the 12V from the Power Supply routed through L511 to pull up the Gate of Q507 via R558. Q507 has the 12V on its Source. When Qp 507 switches on its outputs the 12V to the T-CON.

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Panel power

Once you have confirmed that there is 12V on the Main board side of the LVDS connector, it is time to get to the T-CON itself. Since the T-CON is generally covered by a metal shield, you may or may not be able to get to the 12V TP without removing the shield.
There will always be a 12V fuse protection in 12V line. It will always be the first component the 12V passes once it enters the T-CON. So this is an easy test point to check for the 12V input to the T-CON. If its there the Check the fuse. If it is missing, check the LVDS cable for an open circuit from the Main board to the T-CON. Be sure (with the power turned off) to remove the LVDS cable from the connectors on both ends to investigate.

All T-CONs have a DC-to-DC converter which develops voltages for the T-CON board itself and for the panel. Some have more than one. It is important to check these voltages once the 12V input has been confirmed. To locate the main DC-to-DC converter, look for the larger coils on the board. In the example below, the two larger coils can easily be seen on the upper left hand side. The flat pack IC US1 is the main DC-to-DC converter driver IC. If you do not have any training material you can still pick out some key voltage source TPs from the DC-to-DC converter. Look for “VCC, VDD, HVDD, VGL or VGH” silk screened labels on the board. This T-CON actually has more than one DC-to-DC converter. In some case Replacing the DC-to-DC Converter IC can solve the TCON board fault. If its not then you have to go for a new TCON board.

When there is a video problem it can be difficult to determine if the problem is related to the Main board, the T-CON board or the Panel. Most of the typical T-CON boards (not the 3D FRC T-CONs) have a built in test pattern that can be run to isolate the problem. 

Also remember that to run the Panel Test;
# The Power Supply must be working normally.
# The Backlights must be running normally.
This test can also be used when there is video or the video has a problem.
If there is a Video Problem and the Panel Test works normally, before condemning the Main board be sure to investigate the LVDS cable. 

TCON Board – What is TCON board – What is the Function of TCON board – TCON board Voltages – LVDS Cable Configuration

FUNCTION OF TCON BOARD
The T-CON (TFT Controller) is responsible for;
1. Driving the TFT panel. This is usually accomplished by two LVDS type cables between the T-CON and the panel. The panel cell structure as into Vertical columns and Horizontal rows.
# Horizontal Resolution: On a panel with a resolution of 1920 X 1080 we must have 1920 X 3 columns, because a pixel is comprised on a Red, Green and Blue cell. So there will be 5760 individual cells in rows across the screen. To turn these cells on and off, the panel will use verticaladdress lines or electrodes driven by a small board located inside the panel. In this way we can turnthe colors on and off accordingly to recreate the correct colors required to recreate the image.
# Vertical Resolution: On a panel with a resolution of 1920 X 1080 there will be 1080 horizontal rows of cells running across the panel. These rows are being driven by a small board inside the panel. Byaddressing a particular cell via the vertical columns and turning on a row of cells, only the cells being address by the vertical electrodes will be activated. The number of horizontal rows determine the panels Vertical resolution.
2. TFT: Each cell has is driven by a thin film transistor called (TFT) and a capacitor. When that cells is addressed (turned on) the capacitor will charge and will remain charged until the next refresh cycle.Generally speaking, when the cell has no power applied, it blocks the light from passing through, when it turns on, dependent upon how long it is on, allows more or less light to pass. In this way we can control the brightness level being output by that cell.
3.Panel Voltages: The T-CON is responsible for developing panel voltages. These voltage will vary dependent upon the type of panel utilized. Generally state there will be 4 voltages that are always being delivered to the panel, -5V, 3.3V, 16V and 26V. However, there may be more according to the type of panelbeing used.

Backlights: Since the Liquid crystal panel does not generate any light of its own, there must be a light source behind the panel. This light source is called the “Backlights” called B\L here after. The B\L can be either florescent (EEFL or CCFL) or they can be LED. 

Voltage Source for the T-CON

The T-CON Voltage Source will always be provided from the Main board. However, the Main board does not actually generate the T-CON source voltage. All the Main board does is switch on and off the voltage coming from the Power Supply. The Power Supply generates a 12V supply that is sent to the Main board. When it is time to turn on the T-CON, the Microprocessor will send out a command that turns on the T-CON 12V and this voltage is routed through LVDS cable to the T-CON.

Voltages that the T-CON Generates.

When the T-CON receives the 12V from the Main board, it turns on DC-to-DC converters on the T-CON board to generate several voltages. Some are used on the T-CON board itself (3.3V and 1.0V) and some are sent to the panel’s internal horizontal and vertical driving board. Generally speaking, there are 4 primary voltages sent to the panel. They are -5V, 3.3V, 16V and 26V. It is important to always check for these voltages if you having problems with the T-CON board. But always remember there may be more voltages generated and sent to the panel on different types of panels.

LVDS Cable (Low Voltage Differential Signal)

The picture below shows the LVDS cables routed from the Main board to the T-CON.

About LVDS Cable.

The LVDS (Low Voltage Differential Signal) Cable in a LCD TV is responsible for two primary jobs.
1. VIDEO and TIMING SIGNALS: To deliver video signals that have been processed into a positive and a negative going pair of signals. These pair of signals are sent is groups which equal the resolution characteristics of the panel. As an example if the panel is a HD panel, the differential pair will be 10 lines carrying positive and negative video data. And there will be two line carrying positive and negative clock signals. If the panel is a full HD panel, it will have double the amount of lines.
The positive signals will be designated on the schematic with the suffix of (P or +) and the negative lines will be designated as (N or -). If you take one pair of video signals and look at them on a Oscilloscope, they will be and exact mirror of each other. By using a differential pair, the circuitry can isolate and remove the noise on the line by addition and it can extract the actual signal by subtraction which will double the signal level.
2. T-CON VOLTAGE: The T-CON board needs voltage to operate, the LVDS cable will deliver the T-CON’s operational voltage form Mother board.
If the LVDS cable is suspected of having a problem, most often it can be seen visually. Look for the cable being bent which cause the internal paths to be broken. The cable can be cut, or cracked or physically damaged in some way. The other problem that the LVDS cable can have is the continuity of contacts that are on the side that goes into the connector. This can only be seen by unlocking the cable connector and removing the cable. Then flipping the cable so the contacts points can be seen. See if they are separated from the cable. They could be curled up or even bent over and pressed onto another line causing a short. One other thing to look for is the cable being incorrectly inserted into the connector, (improperly seated).

When the LVDS cable is causing a problem, the symptom can be many. Lines in the picture, portions blocked out, every other line missing, noise pattern on the screen. Missing 12v to the TCON board causing a black or no picture symptom, etc… It can even shut the TV down if the 12V is shorted.

LVDS Cable Connectors

The LVDS cable can use different types of connections to the Main board and to the T-CON.
Below shows some of the types of LVDS cable connections being used in LCD TVs.

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LVDS Connector Contents

Pin	Label	Run	Check Diode
1	Gnd	Gnd	Gnd
2	3D_Sync_Out	0.03V	2.34V
3	*V_SYNC	3.33V	1V
4	SDA3_3.3V	3.34V	1.73V
5	SCL3_3.3V	3.34V	1.73V
6	FRC_RESET	3.32V	Open
7	n/c	n/c	n/c
8	3DTV	0V	Open
9	3D DIM	0V	Open
10	3D_DIM_2	0.05V	Open
11	n/c	n/c	n/c
12	RRXA0-	1.17V	1.67V
13	RRXA0+	1.19V	1.67V
14	RRXA1-	1.19V	1.67V
15	RRXA1+	1.17V	1.67V
16	RRXA2-	1.22V	1.67V
17	RRXA2+	1.14V	1.67V
18	Gnd	Gnd	Gnd
19	RRXACK-	1.16V	1.67V
20	RRXACK+	1.20V	1.67V
21	Gnd	Gnd	Gnd
22	RRXA3-	1.20V	1.67V
23	RRXA3+	1.14V	1.67V

Pin	Label	Run	Check  Diode
24	RRXA4-	1.26V	1.67V
25	RRXA4+	1.08V	1.67V
26	Gnd	Gnd	Gnd
27	n/c	n/c	n/c
28	RRXB0-	1.19V	1.67V
29	RRXB0+	1.19V	1.67V
30	RRXB1-	1.19V	1.67V
31	RRXB1+	1.16V	1.67V
32	RRXB2-	1.2V	1.67V
33	RRXB2+	1.14V	1.67V
34	Gnd	Gnd	Gnd
35	RRXBCK-	1.16V	1.67V
36	RRXBCK+	1.2V	1.67V
37	Gnd	Gnd	Gnd
38	RRXB3-	1.22V	1.67V
39	RRXB3+	1.14V	1.67V
40	RRXB4-	1.26V	1.67V
41	RRXB4+	1.09V	1.67V
42-46	Gnd	Gnd	Gnd
47	n/c	n/c	n/c
48-51	PANEL_VCC	11.59V	Open