Sunday, January 01, 2017

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 vertical address lines or electrodes driven by a small board located inside the panel. In this way we can turn the 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. By addressing 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 panel being 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.

CLICK ON THE IMAGE TO ZOOM IN 
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