Analysis of Common Problems of LCD Screen: Black Screen (Hardware)

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Analysis of Common Problems of LCD Screen: Black Screen (Hardware)

In the previous issue: “Analysis of Common Problems of LCD Screen: Black Screen”, we mentioned that when the LCD screen module is black during the screen-pointing process, the first step is to observe whether the backlight is on. If the backlight is not on, we need to analyze the factors affecting the backlight such as voltage and current (please read the previous article for details). But if the backlight is already on normally, where should we start when the LCD is still black? In this issue, we will provide you with ideas for solving this problem from a hardware perspective.

 

  1. Interface verification First, when we use the motherboard to light up a screen, we need to confirm the following three points one by one: 1. The interface type is consistent. The following 4 definitions are the more common interface types of LCD screens on the market: RGB, LVDS, MIPI, eDP.
  2.  The line sequence definition is consistent. The line sequence refers to the order in which the signal lines are arranged in the interface. In order to ensure that each signal line is correctly connected to the corresponding pin, it is necessary to check that the interface definitions of the motherboard and the LCD screen are consistent, including the number and definition of pins.

interface

  1. The first pin position of the interface must correspond. Take the following figure as an example. The LCD screen is arranged from top to bottom as 1→40. Use the same direction connection line to match the LCD screen and the motherboard 1pin to 1pin, and 40pin to 40pin. If either end is arranged as 40→1, you should consider using a reverse connection line.

mini 40 pin

 

When lighting up the screen, the interface definition must be consistent. When the interface definition is uncertain, do not blindly power on to avoid damaging the screen or motherboard.

If the interface or connector type is inconsistent, we can use the adapter cable to bridge. For example, if the LCD screen is an eDP interface type, but the motherboard only supports LVDS, we can use the signal adapter board to achieve the conversion between the two, as shown below:

mother board

2)Interface contact type

After ensuring that the interfaces on both ends are consistent, let’s understand the common contact methods between motherboards and screens on the market. The following are some common plug-in types:

FFC

FFC type, common consumer tablet scenarios

FPC

FPC types, common consumer tablet scenarios

FFC+METAL SEAT

FFC+metal base type, common laptop NB screen

Dupont

DuPont port type, common industrial control scenarios

board to board

Board-to-board type, common mobile phone screen scenarios

The plug-in type and stability of the connector directly affect the signal transmission effect between the motherboard and the LCD screen. For different plug-in types, the designed adapter cable needs to ensure consistency and strictly control the dimensional tolerance. This can keep it stable during plugging and ensure the stability and reliability of signal transmission.

3)How to ensure that the motherboard and screen are consistent in definition and the connection is stable Use the cable to connect the motherboard and the screen. You can use the conduction position of the multimeter to check the signal conduction one by one to ensure that all signals are connected normally. As shown in the figure below:

multimeter

4)Customer Cases A customer reported that the screen occasionally went black or white. After returning to the factory for inspection, our fixture test showed normal results. So we suspected that there might be a poor contact problem and asked the customer to provide a drawing of their adapter cable. The following figure shows the customer’s plug-in method:

case

After the secondary element measurement, we found that the thickness of the customer’s FPC was 0.15mm, while the drawing indicated 0.19mm±0.03mm. We suggested that the customer adjust the thickness tolerance. Since then, no similar problems have occurred.

 

For more information about LCD screens, please follow the ZOYO Touch Display Company.