Have novices encountered this situation when installing an LED screen for the first time - when they plugged in the power, they found that the screen did not light up, and they were anxious to find that little thing called a control card all over the world? Last month, a guy who runs a milk tea shop complained to me, saying that the display screen he bought suddenly went black, and the repairman came and went straight to the lower right corner of the back of the screen and fixed the problem in 5 minutes. Today we are going to take a look at this mysterious control card, and I guarantee that you will never be "blind" again after reading it.

​​What does the control card look like? ​ ​
To be honest, I was confused when I took apart the LED screen for the first time. The metal box with the heat sink attached is about the size of a palm, and the densely packed interfaces on it look like the back of an old video recorder. It’s good to remember these three characteristics:

• The power cord and network cable must be connected (professionally called RJ45 interface)
• There are honeycomb heat dissipation holes on the surface
• Labeled with QR code or SN serial number

When installing curved advertising screens in shopping malls last year, an intern almost threw away the control card as scrap metal. Fortunately, the master's sharp eyesight revealed this "heart part" in the packaging foam. So novices must be careful when unboxing and don’t dispose of the accessory box as garbage.

​​Five common hiding places revealed​​
The installation position of the control card directly affects the maintenance efficiency. According to my experience of installing more than 300 screens in the past few years, there are three main situations:

1. ​​outdoor advertising screen​ ​: 90% is hidden in the waterproof compartment in the upper right corner of the back of the screen, which can be seen by opening the locked metal cover. There is a trick - follow the direction of the power cable routing, and you will basically not go wrong.

2. ​​Transparent window screen​ ​: Such high-end products usually integrate the control card inside the frame. The last time I installed a screen with a transmittance of 86%, its control card was hidden in the card slot of the aluminum alloy frame, and you had to use a special tool to take it out.

3. ​​stage rental screen​ ​: In order to facilitate quick disassembly and assembly, the control card is directly hung on the side of the box. Pay attention to waterproofing and anti-collision here. The most unique design I have seen is a plug-in installation with a silicone protective cover. Changing the card is easier than changing the mobile phone case.

​​The painful lesson of choosing the wrong control card​​
Don’t think that the control card is just an accessory that you can buy casually. Last year, when installing a floor tile screen in a gym, the customer used a mismatched control card, resulting in serious smearing. Later, it was discovered that the refresh rate was not up to standard - professional performance screens must use control cards that support 1920Hz or above, but the one they used could only support 800Hz.

Here are three key points to avoid pitfalls:

• The indoor screen control card depends on the gray scale (at least 14bit)
• Outdoor screens must choose wide-temperature models (can work from -30℃ to 80℃)
• Transparent screens require a special card with brightness compensation function

There is a counter-intuitive knowledge point: the storage capacity of the control card is more important than you think. For example, to do dynamic effect switching, at least 32G of cache space is required. The most exaggerated case I have ever seen was that a shopping mall used an 8G control card to play 4K video, and it would freeze every 15 seconds. Customers thought it was a screen quality problem.

​​The ultimate question: How to save yourself when the control card is broken? ​ ​
I've been asked this question no less than fifty times. Let me start with a real case: Last month, the menu screen of a hot pot restaurant went black, and the boss was extremely anxious. I asked him to do these three steps:

1. Check whether the control card indicator light is always on (green light means normal)
2. Listen for a "beep" startup sound when restarting
3. Use your phone's flash to look at the screen to see if there is any faint display

It turned out that the network cable interface was oxidized, and the problem was solved by polishing the gold finger with an eraser. Here is a piece of industry knowledge: The life of the control card is actually longer than the screen. It will not break down after five or six years of normal use. Most failures are caused by poor interface contact.

The editor’s experience of blood and tears over the years is just this:​ ​The control card is like a car engine. It cannot be seen normally but if something goes wrong, it will be shut down immediately.​ ​. Next time you encounter an abnormal display, don’t rush to report for repair. First look for the control card in the location I mentioned. If you still can't figure it out, remember to ask the manufacturer for a 24-hour technical support hotline, which is ten times more reliable than searching for tutorials online. If you have encountered any weird control card failures, please feel free to chat in the comment area, maybe I can help.

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