Nowadays, the number of LCD TV users is increasing, and the number of repairs is also increasing. The maintenance that corresponds to cheap prices and quality will increase, and almost every day during maintenance, we will encounter problems
When replacing the screen or TV driver board, it is common to encounter models that are different from the original. How do you repair them? Perhaps everyone's methods are different, but everyone's goal is the same - to solve the problem of maintenance. However, many repair technicians encounter LCD screens that are broken and don't know how to start. Here, I will share with you.
1、 Research on Connection Signals
1. The voltage and power of the logic circuit power supply for the screen.
(1) The voltage values can be divided into 5V and 12V, based on the specifications of the screen, which does not comply with the modification on the TV board.
(2) The power consumption of LCD televisions is mainly on the backlight, which accounts for the total power consumption
More than 80%, the larger the screen size, the more backlights there are, the longer the length, and the higher the power consumption. Generally speaking, pairing
A large screen requires a high-power power board.
The power consumption of backlights of various sizes is approximately as follows: 25W for 17 inches, 38W for 20 inches, and 67W for 26 inches,
32 inch is 110W, 37 inch is 145W, and 42 inch is 160W.

2. Power supply voltage and control signal of inverter
(1) The power supply voltage of inverters can be divided into 12V and 24V, and generally around 20 inches and below is 12V. 30 inch left
Right and below are 24V.
(2) There are two types of control signals
The first is the enable signal for controlling the operation of the inverter's control chip, which is Backlight on/off Control in the screen specification book
Voltage. The high/low level output of the TV driver board. There are differences in the high level regulations for screens that need to be noted, some of which are
3.3V, some regulations require 5V, as the minimum value for high levels is 2V, it may not be considered when changing screens.
The second type is the backlight brightness adjustment signal, which is stated on the screen specification sheet as PWM Dimming Control Voltage
There are several voltage values as follows: 0V~3V, 0V~3.3V, 0V~5V. Be sure to change the screen when changing, otherwise
The adjustment range of brightness is not sufficient.
2、 LVDS signal
1. What is LVDS signal
LVDS (Low Voltage Differential Signaling) stands for Low Voltage Differential Signal, which is a type of signal
Low swing differential signal technology, which enables signals to travel at a speed of several hundred Mbps on differential PCB pairs or balanced cables
Rate transmission, with low swing and low current driving output, achieves low noise and low power consumption.
Because the LVDS signal has a DC bias level of 1.2V, a swing amplitude of ± 350mV, and interference between the - and+lines
It can also offset each other. So the anti-interference ability is very strong, so the connection between the TV driver board and the LCD screen is basically the same
It is it that connects.
The LVDS physical interface uses a 1.2V bias voltage as the reference, providing a swing of approximately 350mV. The LVDS driver is composed of
The LVDS receiver consists of a current source that drives a differential pair (usually 3.5mA) and has a high input resistance
Resistance, therefore most of the current output by the driver flows through a matching resistor of 100 Ω and is generated at the input of the receiver
A voltage of approximately 350mV.

It takes time to change from the logical "0" level to the logical "1" level. Due to changes in the physical level of LVDS signals
Between 0.85V and 1.55V, the time it takes for the logic "0" level to change to the logic "1" level is faster than the TTL level
So LVDS is more suitable for transmitting high-speed changing signals. Its low-voltage characteristics and low power consumption.
2. The relationship between the number and logarithm of LVDS signal groups and the resolution and grayscale level of the screen
The signal of LVDS interface is also divided into 6-bit 4-group differential, 8-bit 5-group differential, and data cable names are 0-0+, 1-1+,
If it is a 6-bit screen, there is no signal for the group of 3+-2+, CLK - CLK+, 3+-3+.
The standard clear screen is usually 1366 × With a resolution of 768, there is only one set, and one pair of lines is a clock line (CLK+),
CLK -, the other four pairs are data cables (RX0+, RX0-; RX1+, RX1-; RX2+, RX2-; RX3+, RX3-),
The corresponding three primary colors RGB are eight bits, namely R0~R7, G0~G7, B0~B7, and the grayscale level of the screen is 128 levels.