Comprehensive analysis of LED display repair skills

Comprehensive analysis of LED display repair skills

I. Basic preparation for LED display repair

To repair LED display, you need to prepare the corresponding tools, such as tweezers, hot air gun, soldering iron, multimeter, test card, etc., and also prepare auxiliary materials such as solder paste (tin wire), flux, copper wire, glue, etc.

II. Common LED display fault types and repair methods

(I) Local "dead light" problem Local "dead light" means that one or several lights on the LED display are not lit. The cause of this situation is usually a problem with the light itself, which may be damp or the RGB chip may be damaged. The repair method is to replace the LED lamp beads with factory-provided spare parts, using tweezers and hot air guns, and retest with a test card after replacement.

(II) "Caterpillar" problem The "caterpillar" phenomenon refers to the appearance of a long dark-bright strip on part of the LED display when the LED display is powered on but there is no input source. The root cause is leakage of the chip inside the lamp or short circuit of the IC surface line behind it. For chip leakage, you can use a hot air gun to blow hot air along the leakage area to make the internal leakage chip connection swell, but you still need to find and replace the hidden lamp beads. If the row tube circuit on the back IC surface is short-circuited, you need to use a multimeter to measure the relevant IC pin circuit and replace a new IC.

(III) Partial color block missing When a small square block of different color appears when the LED display screen is playing normally, this problem is generally caused by the color IC behind the color block being burned out. The solution is to replace a new IC.

(IV) Partial black screen and large area black screen When the black screen phenomenon occurs, first consider the power factor. Check whether the LED power indicator light is working properly. If the indicator light is not on, it is mostly due to power damage. Replace a new power supply with the corresponding power. At the same time, check whether the power cord of the LED module corresponding to the black screen is loose. Re-tightening the wire head may solve the problem.

(V) Local garbled code Local garbled code refers to the phenomenon that messy, irregular, and possibly randomly flashing color blocks appear in a local area when the LED display screen is playing. First, check the signal line connection problem, check whether the cable is burned, whether the network cable is loose, etc. If there is no problem with the signal connection, you can swap the problematic LED module with the adjacent normal playing module to determine whether the LED module is damaged. The damage is mostly caused by IC problems, and the repair is more complicated.

III. Relevant knowledge of LED display interface and driver chip

(I) 74HC138 8-bit binary to decimal decoder Pin 8 is GND power ground, Pin 15 is VCC power positive pole, Pins 1 to 3 are A, B, C binary input pins, Pins 4 to 6 are chip select signal control pins, only when Pins 4 and 5 are "0" and Pin 6 is "1", it will be selected, and the output is controlled by A, B, C signals. Any other combination will not be selected, and the output of Y0 to Y7 is all "1". By controlling the selection pin, it can be cascaded to expand it to sixteen bits.

(II) 74HC595 LED driver chip Pin 8 is GND power ground, Pin 16 is VCC power positive pole, Pin 14 is DATA serial data input port, display data enters from here, must have the cooperation of clock signal to shift in. Pin 13 is EN enable port, when this pin is "1", QA to QH ports are all "1", when it is "0", the output of QA to QH is controlled by the input data. Pin 12 is STB latch port, when the input data is transferred to the register, only a latch signal can be provided to send the shifted data to QA to QH ports for output. Pin 11 is CLK clock port, each clock signal will shift one bit of data into the register. Pin 10 is SCLR reset port, as long as there is a reset signal, the data shifted into the register will be cleared, the display screen generally does not use this pin, usually connected to VCC. Pin 9 is the DOUT serial data output terminal, which transmits data to the next one. Pins 15, 1 to 7 are parallel output ports, that is, drive output ports, which are used to drive LEDs.

(III) 4953 row drive tube It has two CMOS tubes inside, pins 1 and 3 are VCC, pins 2 and 4 are control pins, pin 2 controls the output of pins 7 and 8, and pin 4 controls the output of pins 5 and 6. Only when pins 2 and 4 are "0", 7, 8, 5, and 6 will output, otherwise the output is in high impedance state.

(IV) TB62726 LED driver chip Pin 1 is GND power ground, Pin 24 is VCC power positive pole, Pin 2 is DATA serial data input, Pin 3 is CLK clock input, Pin 4 is STB latch input, Pin 23 is output current adjustment terminal, connected to resistor adjustment, Pin 22 is DOUT serial data output.

IV. Detection method for LED display repair

(I) Short circuit detection method Set the multimeter to the short circuit detection gear (some are diode voltage drop gear or resistance gear, generally with alarm function), and detect whether there is a short circuit. After a short circuit is found, it should be handled first to prevent burning other devices. This operation must be performed when the circuit is powered off to prevent damage to the meter.

(II) Voltage drop detection method Set the multimeter to the diode voltage drop detection mode. Because all ICs are composed of many basic units, but they are miniaturized, when current passes through a certain pin, there will be a voltage drop on the pin.

V. Troubleshooting and treatment of the entire screen failure

(I) The entire screen is not lit (black screen) Check whether the power supply is powered on, check whether the communication line is connected and whether it is connected incorrectly (synchronous screen), and check whether the green light of the sending card and the receiving card on the synchronous screen flashes, whether the computer display is protected, or whether the display area is black or pure blue.

(II) The display is chaotic, but the signal output to the next board is normal. Check whether the corresponding STB latch output terminal of 245 is connected to the latch terminal of the driver IC or the signal is short-circuited to other lines, check whether the line is short-circuited to the positive pole of the power supply, and replace its driver IC.

(III) Display confusion, abnormal output Check whether the clock CLK latch STB signal is short-circuited, check whether the clock CLK of 245 has input and output, and check whether the clock signal is short-circuited to other lines. Note: Mainly check the clock and latch signals.

(IV) Display lack of color Check whether the data end of the color of 245 has input and output, check whether the data signal of the color is short-circuited to other lines, and check whether the cascaded data port between the driver ICs of the color is open or short-circuited, or has a cold solder joint. The voltage detection method can be used to easily find the problem, check whether the voltage of the data port is different from the normal one, and determine the fault area.

(V) Output problems Check whether the line from the output interface to the signal output IC is connected or short-circuited, check whether the clock latch signal of the output port is normal, check whether the cascaded output data port between the last driver IC is connected or short-circuited to the data port of the output interface, whether the output signals are short-circuited to each other or short-circuited to the ground, and check whether the output wiring is good.

VI. Services and processes for LED display screen repair

(I) LCD splicing screen series Including the repair, installation and recycling of ultra-narrow LCD splicing screens such as 32 inches, 40 inches, 43 inches, 46 inches, 47 inches, 49 inches, 50 inches, 55 inches, and 65 inches, as well as the repair, installation and recycling of touch-screen all-in-one machines, advertising machines, monitors, electronic whiteboards, nano-smart blackboards, and queuing systems.

(II) LED display screen series Provides LED display screen production and installation services, including indoor high-definition full-color screens, outdoor full-color outdoor screens, indoor and outdoor single and double-color LED subtitle screens, etc. At the same time, it provides LED display screen repair and maintenance services, including the repair and debugging of single-color screens, double-color screens, and full-color screens, covering the handling of various fault problems. It also provides LED display screen steel structure design and construction services, including the production and installation of various structural types.

(III) Large screen supporting equipment Including the repair of high-definition matrix, decoding matrix, decoder, splicing processor, video processor, image processor, high-definition distributor, etc.

The maintenance process is as follows: the customer reports a fault, the company registers and accepts the report and assigns a technician, the technician contacts the customer to come to the customer's home, conducts an on-site inspection and presents a price list, after the maintenance is complete the warranty form is filled out and the user confirms the signature, the company returns the visit, the customer confirms the maintenance result, and the warranty begins.