【 Weak current College 】 led screen repair method 】

1. circuit basis and the purpose of the common components

1, resistance: in the circuit played the role of current limiting voltage divider. Use R said that the unit ohm (Ω). In pixels of the product resistance more used to limit the current size.

2. capacitance: every other DC-AC, in pixels, of the products used for filtering. Unit c, (F) law.
Case study: common 0805 package 104PF capacitor, is used to filter out the circuit of high frequency voltage ripple, Electrolytic Capacitor-470UF 16V, used for filtering out/low-frequency voltage ripple. Is to filter out interference and improve circuit of anti-interference ability, the circuit stable work.
3. role: IC IC
Example: our 74HC595, MBI5026 are IC.

74HC245 role: signal power amplification.

1 foot DIR, input output port translation, DIR = "1" high level "A" is set by the client to enter the "B"-end output, DIR = "0" low level signal by "B" end-to-enter "A" end output.
2 ~ 9 foot "A" signal input output, A1 = B1,,,,,, A8 = B8, A1 and B1 is a group, if DIR = "1" G = "0" then enter A1, B1 output with other classes. If DIR = "0" G = "0" then enter A1 B1, other similar output.
11 ~ 18 foot "B" signal input, output, and "A" end, not in the description.
19 feet G, enable, if the foot is "1" A/B-end signal will not only provide "on-0" A/B-end was enabled, the foot that is up to the switch.

10 feet to GND, the power supply.
20 feet VCC, power cathode.
74HC04 role: 6 bits of the inverter.
7 pin GND, power.
14 foot VCC, power cathode.
Signals from A client-side input Y side inverting output, A1 and Y1, other groups, and so on. Example: A1 = "1" Y1 = "0", A1 = "0" Y1 = "1", the other set of features.

74HC138 role: eight-bit binary translation decimal decoder.
8 pin GND, power.
16 foot VCC, power cathode
1 ~ 3 feet A, B, C, binary input pin.
4 ~ 6 foot piece selected signal control, only in 4, 5 feet to "0" to "6 feet, 1" will be gated, output is A, B, C signal control. Any other combinations will not be gated and Y0 ~ Y7 output all "1".
By controlling the gated feet to cascade, so as to extend to 16 bits.
Case study: G2A = 0, 0, G2B = G1 = 1, A = 1, B = 0 C = 0, Y0 Y1 to "0" to "Y7 ~ 1", for more details, see truth table.

The role of the 74HC595: LED driver IC, 8 displacement bit latches.
8 pin GND, power.
16 foot VCC, power cathode
14 foot DATA, serial data input, display the data from this entry, you must have the cooperation of the clock signal to move into.
13 feet EN, enable port, when the PIN is "1" QA ~ QH mouth all "1", "0" QA ~ QH output from input data control.
12 foot STB, latches, and when you enter data in the incoming registers, only supply a latch signal can be moved into the data sent to QA ~ QH port output.
11 feet CLK, clocks, each clock is moved into an old data to the register.
10 foot mouth SCLR, reset, as long as the reset signal that registers the data within the move will be empty, display instead of the foot, General add VCC.
9 foot DOUT, serial data output, data to be passed on to the next.
Sections 15, 1 ~ 7 feet parallel output is driven output, LED drivers.

4953: line drive pipe, the power tubes.
Its interior is both CMOS tube, 1, 2, 3 foot VCC, 4 2 foot control foot, foot control, 7, 8 feet of output, 4-5 foot control, the output of 6 feet, only when the 2, 4 feet to "0", 7, 8, 5, 6, will be output, the output is high impedance state.
MBI5024 role: LED driver IC, 16 bit latch for displacement.
1 foot to GND, the power supply.
24 foot VCC, power cathode
2 foot DATA, serial data input
3 foot CLK, clock input
4 foot STB, latch input
23 foot output current adjustment end, resistance adjustment
22 feet DOUT, serial data output
21 feet EN so that able to input
Other features and similar, only the 74HC595 MBI5024 is a 16 bit latch for displacement and output current adjustment function, but in parallel output does not appear on high, only the high-impedance state and low level status. 74HC595 parallel output with high level and low level output.

Second, the led display common signal of understanding
CLK clock signal: available to shift register shifting pulses, each pulse will cause data moved into or out of a bit. The data on the data port must be coordinated with the clock signal to normal shipping data, data signal frequency is the frequency of the clock signal 1/2 times. In any case, there are exceptions when the clock signal, will make the complete Board show disorganized.
STB latch signal: will shift registers the data sent to latch, and its data content through the driver circuit lit LED displayed. But because of the driver circuit is EN enable signal control, whose premise of light must be enabled to open. Latch signal also needs to be coordinated with the clock signal to show the full image. In any case, when a latch signal with exception makes the complete Board show disorganized.
EN enable signal: full screen brightness control signal, and is also used to screen blanking. As long as the adjustment of its duty to control brightness changes. When the signal when an exception occurs, the screen will be lit, Dim light or smearing.
Data signal: display image needed data. Must be coordinated with the clock signal to transmit data to any of the display. General display in red-green-blue signal separation of data, if a data signal circuit to positive or negative, then the corresponding that color will appear fully lit or unlit, when the data signal is suspended when the corresponding color display case.
ABCD line signal: only in dynamic scanning is displayed there, ABCD is a binary number, A is the lowest bit, if you use the binary representation of the ABCD signal control maximum range is 16 lines (1111), 1/4 scans can be as long as AB signal because AB signal indicates that the range is 4 lines (11). When the line controlsignals when an exception occurs, it will appear dislocation, the highlight or images overlap.

III. common troubleshooting tools

Judge issues must first master after the time of processing, the manifest, serious issues to deal with, small.
Short circuit should be the highest priority.
1. resistance detection method, the multimeter to resistance, detection of a normal circuit board of a certain point to resistance value, and then detects another piece of the same circuit board with a point and normal resistance values are different, if different then determines the scope of the problem.
2. voltage detection method, the multimeter to voltage rail, test the suspected circuit of a point to ground voltage, a comparison is similar to the normal value, and determines the scope of the problem.
3 short circuit detection method, the multimeter to short-circuit detection gear (some are diode drop stalls or resistance, generally with alarm function) to detect if a short circuit, the discovery of the phenomenon should give priority to solving the short circuit, so that it does not burn other devices. The Act must be in the circuit power of operation, to prevent damage to the table.
4. pressure drop detection method, the multimeter to diode drop detection, because all of the IC are fundamental to many unit parts, only small size, so when it's a PIN on the current adoption, in the presence of voltage drop on the PIN. Generally the same models of IC same PIN on the pressure drop, depending on the pressure drop pin value comparison is good or bad, you must power off of the circuit. This method has limitations, such as detection devices are high, it is not detected.
4. cell plate alignment patterns and common processing steps
1/16 unit plate alignment method:

1/8 unit sheet 3 alignment method:

Static light plate alignment method:
The only way for the section alignment. On unknown unit panels, repair before to measure to know whether the alignment style, convenient next maintenance to improve work efficiency.
Cell board failure:
A complete Board is off.
1. check the power supply and signal cable is connected.
2. check whether the test card to identify the interface, the test card is not recognized by the red light flashing, check the light plate with test card with power supply, or light Board interface has signal and to a short circuit causing unrecognized interface. (Intelligent test card)
3, there is no deficiency detected 74HC245 welding short circuiting, 245 on corresponding enabling (EN) signal input output pin is soldered or short-circuit to other lines.
Note: check the power and enable (EN) signal.
B £ ® oblique in points, of the law when scanning interface is not lit display overlapping
1. check the A, B, C, D signal input to 245 is there between the broken line or soldered and short circuit.
2. detection of 245 corresponding A, B, C, D output and 138 between circuit breaker or soldered and short circuit.
3. testing A, B, C, D the signal between the short circuit or short circuit of a signal and ground.
Note: the main test ABCD line signals.
C £ ® full bright one line or several lines not lit
1. detection of 138 to 4953 whether circuit breaker between lines or soldered and short circuit.
D £ ® in the line scan, two lines or lines (usually multiples of 2, regularity of) at the same time light
1. testing A, B, C, D the signal between the short circuit.
2. detection of 4953 outputs are short circuit with the other outputs.
When you full bright E. a single-point or multi-point (irregular) is not lit
1. Locate the module corresponds to the control of foot measurement is our short circuit.
2. replace the module or a single lamp.
F.-when a column or columns is not lit
1. in control column found on the module pin, if measured and driver (74HC595/MBI5026) output-side connection.
There is a single point G £ ® or single row highlighting, or highlighting the entire line, and not managed
1. check whether the column and the power to the circuit.
2, testing whether the row and the power of positive electrode short circuit.
3. replace the driver.
H. display confusion, but the output to a plate of good signal
1. detection of 245 corresponds STB latch output and driver IC latch side is connected or signal is short circuit to another line.
I £ ® display confusion, the output is not working properly
1. detection of clock CLK latch STB signal is shorted.
2. detection of 245 clock CLK for input and output.
3. detection of the clock signal is shorted to other lines.
Note: the main test clock with latch signal.
Lack the color displayed J.
1.Detection of the 245 color data end if input and output.
2. detection of the color data signal is shorted to other lines.
3, detect the color driver between concatenated data port is open or short circuit, the virtual welding.
Note: you can use voltage detection method is easier to find the problem, test data of the normal voltage and to determine whether different fault zones.
K. output problems
1. detection output interface to the signal output IC circuit is connected or short circuit.
2. detection output clock latch signal correctly.
3. testing the last driver of the concatenated output data port with the output interface data port connections or is shorted.
4. output signals if there is mutual short circuit or short to ground.
5. check the output of wire is good.
Full size:
A. full screen does not light (black)
1, testing whether the power supply.
2. detection of communication cable is connected, there is no mistake then. (Synchronous screen)
3. Synchronize screen test send card and receives the card address there is no blinking green light.
4, whether the protection of the computer monitor, or the display area is black or blue. (Synchronous screen)
B. block cell plate is off (black)
1. how many sheets of transverse direction continuously do not light up, check for normal cell plates and abnormal cell plates between the cable connection is connected; or chip 245 is normal,
2. continuous longitudinal direction a few panels, check off the power supply correctly.
C. no uplink modules
1, check row feet and 4953 output pin are connected.
2. check whether the normal 138.
3 4953 perm or burned down.
4 4953 has a high level.
5. check 138 and 4953 control pin are connected.

By calculating the led display viewing distance, you can help us identify the most suitable distance from the Viewer, and the best angle, the led display will be able to play it unique.
Three RGB color mixing distance of a single color mix of distance: pixel spacing (mm) * 500/1000
Minimum viewing distance to display smooth image distance: pixel spacing (mm) x 1000/1000
The best viewing distance to the viewer can see a clear picture of distance height: pixel spacing (mm) a × 3000/1000
The most distant viewing distance: screen height (m) x 30