LED display fault complete

Source: RUI JIN

2018-04-01 08:37:04



This article lists the LED display screen a variety of issues, including short-circuit processing, cell board troubleshooting, outdoor (module) troubleshooting, the entire screen troubleshooting, control system troubleshooting, drive part of the problem processing. More detailed and worth collecting.

Judgment of the problem must be dealt with by the primary and secondary modes first, with obvious and serious first steps and minor problems afterwards. (short circuit should be the highest priority)

First, short circuit processing
1. The resistance detection method adjusts the multimeter to the resistance file, detects the resistance value of a certain point of a normal circuit board to the ground, and then detects whether the same point of the same circuit board is tested with the normal resistance value. If it is different then the scope of the problem is determined.

2. The voltage detection method will adjust the multimeter to the voltage level and detect the voltage of the point where the circuit is suspected to have problems. Compare whether it is similar to the normal value, otherwise, determine the range of the problem. 3, short-circuit detection method, the multimeter to short-circuit detection block (some diode downshift or resistance file, generally with alarm function), detect whether there is a short circuit phenomenon, found that short-circuit should be prioritized, so that it does not burn out Other devices. This method must be operated with the circuit powered down to avoid damage to the watch.

4, pressure drop detection method, the multimeter to adjust the voltage drop detection diode, because all of the IC is composed of many basic units, but miniaturized, so when there is a current through a pin, There will be a voltage drop on the pin. Generally, the voltage drop on the same pin of the same type of IC is similar, and the voltage drop on the pin is better or worse, and the circuit must be operated with the power off. This method has certain limitations. For example, if the device under test is high-impedance, it cannot be detected.

Second, the unit board failure
A. The whole board is not bright
1. Check if the power supply and signal line are connected.
2. Check whether the test card recognizes the interface. The red flashing of the test card is not recognized. Check whether the light board is in the same power ground as the test card, or if there is a short circuit between the light board interface and the ground, the interface cannot be identified. (Smart Test Card)
3. Check whether the 74HC245 is short-circuited by a short circuit or not, and whether the corresponding input/output pin of the 245 signal is pinned or short-circuited to other lines. Note: Mainly check the power and enable (EN) signals.

B. Regular interlaced display overlaps during point sweep
1. Check whether there is any broken wire, or short circuit or welding between A, B, C and D signal input ports.
2. Check whether the 245 corresponding A, B, C, D output terminals and 138 are open circuited or soldered or short circuited.
3. Detect whether the A, B, C, D signals are short-circuited or a signal is shorted to ground. Note: The main test ABCD line signal.

C. One or several lines are not lit when all lights are on
1. Check if the line between 138 and 4953 is open or short circuited.

D. In line scanning, two or more lines (usually a multiple of 2, regular) light at the same time
1. Check if the A, B, C, D signals are short-circuited.
2. Check if the output of 4953 is shorted to other output terminals.

E. There is a single or multiple points (irregular) when the light is bright
1. Find out whether the corresponding control pin of this module measures a short circuit with this one.
2. Replace module or single lamp.

F. One or more columns are not lit when fully lit
1. Find the pin that controls the column on the module and check if it is connected to the output of the driver IC (74HC595/TB62726...).

G. Single or single column highlighted, or entire row highlighted, and uncontrolled
1. Check if the column is shorted to the power ground.
2. Check if the line is shorted to the positive side of the power supply.
3, replace its driver IC.

H. The display is confusing, but the signal output to the next board is normal
1. Check whether the corresponding STB latch output of the 245 and the latch of the driver IC are connected or the signal is shorted to other lines.

I. The display is confusing and the output is abnormal
1, detect the clock CLK latch STB signal is short circuit.
2. Check whether the 245 clock CLK has input and output.
3. Check if the clock signal is shorted to other lines. Note: The main detection clock and latch signal.

J. Show lack of color
1. Check whether the data of the color of 245 has input and output.
2. Detect if the color data signal is shorted to other lines.
3. Check whether the cascaded data port between the driver ICs of this color is open circuited or short circuited and soldered.
Note: The voltage detection method can be used to find the problem more easily, and whether the voltage of the data port is different from the normal one is determined and the fault area is determined.

K. There is a problem with the output
1. Check if the output interface to the signal output IC is connected or short-circuited.
2. Check if the clock latch signal of the output port is normal.
3. Check whether the cascade output data port between the last driver IC is connected to the data interface of the output interface or whether it is short-circuited.
4. Whether the output signals are short-circuited or shorted to ground.
5, check the output cable is good.

L. Eight or 16 dot rows, columns, or dots do not appear bright, long, or dark on the cell board.
1. Visually inspect the failure of the corresponding module pins and leads for short circuit, soldering, and open circuit.
2. Whether the common connection lines between the upper and lower modules and the left and right modules of each cell (the cell board is divided into upper and lower two cells) are normal (set the multimeter and the ring terminal, and measure the input terminals of the module rows and the lead connections of the control inputs). If yes, If it is judged that the module is bad, if it is not, it can be eliminated by directly using the thin wire instead of turning it on.
3, can use a multimeter to directly measure whether a single module is normal, and if so, then determine the internal short circuit between the circuit board and the module, if it is judged as a bad module, replace it with the same type of module.

M. A few lines or entire cells appear on the cell board (the cell board is divided into upper and lower two cells), which are off, long, and dark.
1, visual inspection of the corresponding line tube, through the inductor, integrated circuit is a virtual weld, short circuit, open circuit, and if so, the short-circuit at the disconnect and re-welding at the virtual weld, disconnected.

2, with a multimeter to measure the output voltage of each line tube is normal (meter measurement method: black table pen to GND, red meter to measure the voltage of each pin); if so, then determine the line output and the corresponding module pin open circuit; If not, measure the input of the line pipe is normal; if so, then the line pipe is broken, replace it with the same type of line; if not, measure the output of the corresponding HC138 is normal; if so, determine the output and line of the HC138 The input of the tube is open circuited; if not, the HC138 is judged as bad.

3, with a good 16P cable replacement test, measurement HC138 address input terminal 1,2,3 pin voltage, strobe terminal 4,5 (active low), 6 (active high) and IC power supply If it is normal, if it is, then it is judged as HC138 is bad, and then it is continued with (2). (4) If the 5V connection between two small areas is disconnected, if it is, it can be directly connected with the same power line (the general phenomenon is that the whole area is not bright and dark).

4. Measure the row signal at the input end of the unit board (Cruit finger 26P can be regarded as 13 groups, where 8, 9, 10, and 11 are the four groups of L0, L1, L2, and L3, respectively) whether there is an internal short circuit, open circuit, and input HC244 Whether the rear drive is normal or not, if yes, measure whether the signal input by the HC244 drive input HC138 is normal, and then continue with (2), if not, then judge that HC244 is bad and replace it with the integrated circuit of the same type.

N. The cell appears on the cell board (the cell board is divided into two cells). No red or green.
1. Whether the integrated circuit corresponding to the fault is visually inspected, whether the 26P cable is vacant, disconnected, and whether the 5V power supply is normal (it can be directly replaced with a good 26P cable).

2. 26P connecting wires between the cell boards (pins 1 and 2 of 26P are red signals, 3 and 4 feet are green signals) and the previous cell board output (determining method: take a long 26P cable) If the cross-exchange connection is normal, then it is judged to be a problem behind it; otherwise, if there is a problem) is it normal? If yes, then measure the red signal input to the HC244, and drive whether the 14-pin sent to the HC595 is normal (if yes, and HC595 other If the pins are all normal, then the HC595 is judged to be bad. Replace it with the same type of integrated circuit. If not, check the 26P cable for problems and the input is abnormal.

O. Symptoms: The upper and lower modules in the middle of the cell board (upper and lower cells in the cell board) both lack red, lack of green, or from the beginning to the end of the cell, and are both red and green.
1. Visually inspect the integrated circuit corresponding to the fault on the cell board, such as whether the HC595 is cold-welded, short-circuited, or open circuited; if so, solder the leads.
2. Check whether the 5V power supply is normal.
3, with a multimeter to measure the fault corresponding to the HC595's input 14 feet [HC595's measurement should be divided into red germanium integrated circuit, the order is: red, green (R, G) HC595 9 feet for the signal output, 14 feet for The signal input terminal] voltage is normal; if yes, then judge HC595 is bad (under the condition of other normal power supply), replace with the same type of integrated circuit; if not, check the output voltage of the 9-pin output terminal corresponding to HC595, and the circuit connection Whether the line is disconnected, if not, then it is judged as bad HC595, replaced with the same type of HC595 integrated circuit (replacement of the circuit CM595, pay attention to the circuit leads do not disconnect).

Third, outdoor (module) failure
1. The group is continuously off or abnormal:
Check whether the signal of the first abnormal module is in good contact with the power cable. If there is no LED on the module, there is no power input. Check the power supply (check with a multimeter). The bright spot) indicates that the module has no signal input. Please check whether the input terminal of the cable of the first abnormal module is in close contact. You can remove and insert the test several times. If the problem still can replace the new cable.

2. The single module is off:
Check whether the power supply of the module is good, mainly to check whether the power socket on the module is loose. If the entire module has color confusion or color inconsistencies (but there is a signal input, there is a correct picture) for the signal transmission row County bad contact, re-inserted cable, or replace the tested cable. If you have a good replacement cable still has the same problem, please check the PCB board interface for problems.

3, single light is not bright problem detection method:
Use a multimeter to check if the LED is damaged. If the lamp is broken, change the lamp according to item 5 below. Specific measurement methods: put the multimeter into the resistance X1 file, the black meter of the pointer multimeter is connected to the positive pole of the LED, the red meter is connected to the negative pole (the black pen of the digital meter is connected to the negative, and the red pen is connected). If the LED is bright, the measured lamp is OK, if the lights are not on, the measured light is bad.

4, LED bad point maintenance (out of control point):
After a single lamp test confirms that the LED is damaged, the following maintenance methods are selectively used according to actual needs.
4-1 Frontal Maintenance: Remove the fixed mask screws from the front with a corresponding type of screwdriver (make sure to protect the screws), remove the cover, replace the lamp (please replace the lamp according to the following lamp replacement method), change the lamp and seal the gel After the end, the original mask is restored and the screws are tightened (be careful not to press the lamp when tightening the screws). If there is any glue remaining on the surface of the LED, please carefully remove the colloid.
4-2 Maintenance on the back: Remove the screws from the back side with the corresponding model screwdriver (note the retention screws) and unplug the signal cable. For safety, please do not unplug the power cable to prevent accidents. Carefully move the module from Remove the hole in the sheet metal, move it to the back of the box, and then perform the maintenance of the individual module according to the front maintenance method to change the lamp (please change the lamp according to the lamp replacement method below) or overhaul others.

5, change lights:
Remove the glue around the damaged LED with a sharp tool (such as tweezers), and make the LED pin clearly visible in the line of sight. The right hand clamps the LED with a tweezers, and the left hand uses a soldering iron (a temperature of about 40 degrees Celsius, the high temperature will be LED damage) Contact with solder, and stay for a little while (no more than 3 seconds, if it does not reach the dismantling requirement after exceeding the time, please cool down and try again) Melt the solder and remove the LED with tweezers. Fit the LED lamp that meets the requirements correctly into the hole of the PCB circuit board. (The LED lamp's long leg is positive and the short leg is negative. The PCB's square hole is the LED's positive pin jack. The "round hole" is LED's. Negative electrode pin jack) Melts a little solder wire and sticks it on the iron head. Use tweezers to adjust the direction of the LED to make it smooth. Solder the solder to the LED and the PCB. Use the same type of gel (pH = 7) Seal the LED.

Fourth, the entire screen failure:
A. The whole screen is not bright (black screen)
1. Check if the power supply is powered on.
2. Check whether the communication line is connected or not. (Sync screen)
3. The sync screen detects whether the sending card and receiving card communicate green light flicker.
4. Whether the computer monitor is protected or the display area is black or pure blue. (Sync screen).

B. The whole unit board is not bright (black screen)
1. If several consecutive boards are not in the horizontal direction, check whether the cable connection between the normal unit board and the abnormal unit board is connected; or if the chip 245 is normal,
2. When several boards are not in the vertical direction, check whether the power supply of this column is normal.

C. Lines on the cell board are not lit
1. Check if there is any communication between the line foot and the 4953 output pin.
2, check 138 is normal.
3, check 4953 is hot or burned.
4, check 4953 whether there is a high level.
5. Check whether the 138 and 4953 control pins are connected.

D. Unit board is not bright
1, check 595 is normal.
2. Check whether the corresponding module is connected to the upper and lower modules.
3, check 595 output pin to the module pin is connected.

E. Cell board lack of color
1, check 245 R.G data output.
2. Check whether the normal 595 output pin and the abnormal 595 input pin are connected.
3, detect A, B, C, D signal between the short circuit.
4. Check if the output of 4953 is shorted to other output terminals.

F. There is a single or multiple points (irregular) when the light is bright
1. Find out whether the corresponding control pin of this module measures a short circuit with this one.
2, replace the module or single lamp.

G. One or more columns are not lit when fully lit
1. Find the pins that control the column on the module and check if the output of the driver IC (74HC595/TB62726) is connected.
2. Check whether the module pins and integrated circuits corresponding to the faults on the cell board are soldered, short-circuited, and broken. If yes, solder the pins.
3, with a multimeter to measure the output of the HC595, HC595 output pin: 1,2,3,4.

Fifth, control system failure:
1, the entire screen does not shine or appear square
·Control whether the host is turned on
Is the communication line plugged in?
· Is the sending card inserted?
·Multimedia card and capture card, data cable between send cards