Power supplies for LCD and LED displays. LCD TV Power Supply LCD Power Supply

Monitors on flat panel displays are made using the following technologies: liquid crystals - LCD, plasma and LED. These types of monitors have increased brightness and contrast, good display response time, low power consumption and high-quality three-dimensional image. The absence of electromagnetic radiation eliminates the influence of the monitor on the human body.

The choice and possibility of using monitors depends on material possibilities, but the overpayment for quality is justified even by saving electricity.

It is justified to use an LCD TV as a computer monitor.
A high-quality three-dimensional image, high resolution, sufficient brightness and contrast even at 50% load allows you to use it simultaneously in TV mode and in monitor mode, the time for switching modes does not exceed a few seconds.

When working in monitor mode on a TV, it is possible to reduce the horizontal size from 16:9 to standard 3:4, which will reduce eye fatigue from a wide screen when working in computer mode.
The disadvantages of LCD TVs include a weak power supply, which is supplied separately and does not always withstand prolonged use.

The simple power supply presented in the article allows you to perform mains power using an elementary base.

The advantage of using as a TV monitor is low power consumption and the ability to be powered by an uninterruptible power supply, successfully bringing the computer out of working condition in case of emergency situations in the power supply.

Power supply specifications:

1. Mains voltage 180-230 Volts.
2. Power consumption 60 watts.
3. Output voltage 12 volts.
4. Load current maximum 5 Amperes.

The schematic diagram of the power supply consists of a mains rectifier on a transformer T2, a device for maintaining voltage in the load on a powerful field-effect transistor VT1 with circuits for stabilizing the output voltage and overload protection.

The circuit is assembled on a circuit board and installed with a transformer in a BP-1 type case with dimensions 178 * 92 * 70.

The price of the power supply is 300 rubles.

The network circuits of the TV power supply are equipped with a filter on the transformer T1 and capacitor C1. The network input is protected by a fuse FU1, if necessary, the mains supply is turned off by the SA1 toggle switch.

Transformer T2 is set to the maximum load current, but its voltage can be reduced to 13.6 volts without deteriorating performance and overheating at a mains voltage of at least 210 volts.

The VD1 diode bridge corresponds to KD213B type diodes and is installed without a heatsink.
The voltage of the secondary winding of the transformer T2, rectified by the diode bridge VD1, is smoothed out by the capacitor C2, network noise is additionally filtered by the capacitor C3.

The voltage setting on the load is made on the resistor R2, with its inclusion in the bridge circuit, consisting of the reference voltage stabilization circuit on the resistor R1 and the zener diode VD2 and the voltage setting circuit - R2 and R3.
Resistor R4 allows you to separate the installation circuits and the input circuits of the field-effect transistor VT1 - resistor R5.

The radiator on the field effect transistor must have a size of at least 30 * 15 * 20.
The field-effect transistor VT1 in the source circuit has a wire-wound current-limiting resistor R9 and an overcurrent protection setting resistor - R8.

In the event of a short circuit in the load circuit or an excess of the load current, the increased voltage from the resistor R8, through the resistor R7, is supplied to the control electrode of the analog parallel stabilizer 1DA1. With a sufficient excess of voltage at the control input, the stabilizer opens and closes the gate of the field-effect transistor VT1 to the minus of the power source, the voltage at the load drops from 12 volts to almost zero.

LED indicator HL1 indicates the presence of voltage on the load.

To reduce possible fluctuations in the supply voltage, a high-capacity capacitor C5 is installed in the load power circuit.

The installation of the low-voltage part of the TV power supply circuit is made on a printed circuit board with dimensions of 75 * 40 mm., The surge protector is made separately.
The filter transformer T1 was taken from a failed power supply.

The power supply circuit of the TV does not require special adjustment, it is enough to connect a load to the 12 Volt output for the duration of the test, in the form of a light bulb from a car headlight for fifty candles and set the output voltage to 12.6 Volts with the R2 regulator. Set the resistor R8 to a position at which the voltage on the load stops growing when the slider of the resistor R2 is turned - setting the output voltage.

Temporarily apply voltage to the 1DA1 input from the positive power bus, through a 1-1.5 k resistor, while the light on the load should go out. When the radiator of the field-effect transistor is heated above 80 degrees, it should be replaced with a more powerful one or a network transformer with a secondary voltage of 13.6 volts should be installed, you can simply unwind a few turns of the secondary winding.

The radio components in the circuit are installed for general purposes and can be replaced with Russian-made analogues.
The author used radio components from decommissioned monitors.
When connecting the TV, observe the polarity of the power supply.

The power of the power supply is enough to use it as a charger, in electroplating or as a speed controller for an electric drill, in this case, install the resistor R2 of the SP3 type on the top cover of the device case.

Literature:
1) V.I. Murakhovsky "Computer device". "AST-Press book" Moscow 2004
2) V.P. Konovalov TV Cooler. Radio amateur №4/2007 p.34

List of radio elements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
DA1	Reference IC	TL431	1			To notepad
VT1	MOSFET transistor	IRFP260	1			To notepad
VD1	Diode bridge	S30D40C	1			To notepad
VD2	zener diode	KS210B	1			To notepad
C1	Capacitor	0.1uF 400V	1			To notepad
C2		2200uF 25V	1			To notepad
C3	Capacitor	0.33uF	1			To notepad
C4	Capacitor	0.22uF	1			To notepad
C5	electrolytic capacitor	2200uF 16V	1			To notepad
R1, R4	Resistor	680 ohm	2			To notepad
R2	Trimmer resistor	3.3 kOhm	1			To notepad
R3	Resistor	150 ohm	1			To notepad
R5	Resistor	56 kOhm	1			To notepad
R6	Resistor	1.5 kOhm	1			To notepad
R7	Resistor	510 ohm	1

Internal and external power supplies for LCD monitors.

LCD monitors can be usedinternal and externalpower sources. When repairing, it is necessary to determine the type of power supply for the LCD monitor, the power converter construction schemes, the determination of circuitry solutions and the appointment of any other power supply circuits. At this stage, it is also necessary to determine the element base and the type of microcircuits and transistors used.

Internal power supply located in the monitor case and, as a rule, is a switching converter that transmits AC mains voltage to several output DC power buses (Fig. 1). A distinctive feature of LCD displays with an internal source is the presence of an external 220V connector for connecting a power network cable. The main disadvantage of this arrangement of the monitor is the presence of a high-voltage powerful pulse converter inside it, which can negatively affect the operation of the monitor itself.

Rice. 1. Scheme of the internal power supply of the LCD monitor.

When external power supply In the kit, along with the monitor, an external network adapter is supplied, which is a separate module for converting the AC mains voltage into the required DC voltage with a nominal value of about 12-24V (Fig. 2). Schematically, it is exactly the same pulse converter as in the internal power supply. Such a layout decision makes it possible to exclude the power stage from the LCD monitor, which, ultimately, improves the reliability of the product, as well as the quality of the displayed information.

Rice. 2. Scheme of the external power supply of the LCD monitor.

For the first and second options for building a monitor, the number of output power rails ranges from one to three. A typical option is the formation of tires + 3.3V, + 5V and + 12V at the output. The voltage assignment is as follows:
+5V - used as a standby voltage, as well as for powering digital, analog circuits, the logic of the LCD panel itself, etc.
+3.3V - supply voltage of digital microcircuits.
+12V is the supply voltage of the backlight inverter, and is also used to power the LCD panel drivers.
In the case of using an external power supply, all of the above voltages will be generated from a single 12-24V input bus using DC-DC converters from DC to DC. This conversion can be done either with a linear regulator circuit or with a switching regulator. Linear regulators are used in low-current circuits, and pulse converters in those channels where the current can reach significant values. The DC-DC converter is almost always located on the main control board of the monitor and is an integral part of it.
The construction and implementation of such converters is sufficient typical and different in different monitors only the number of output buses at the output and the element base. The converters are made on the basis of pulse step-down voltage converters, which include a multi-channel PWM chip that controls the output power stage. Adjustment and stabilization of the output buses is performed using PWM technology in feedback circuits.
Repair of the LCD monitor power supply should always be carried out only after preliminary diagnostics of both individual elements and the entire power supply as a whole. Such diagnostics are necessary in order to assess possible damage, identify faulty elements, eliminate repeated failures and the occurrence of interference when the power source is turned on after repair work.

Hello!

In this article, we will take a look at lcd tv power supply Samsung BN44-00192A , which is used in devices with a screen diagonal of 26 and 32 inches. We will also analyze some typical malfunctions of this module.

All components of this power supply located on the same board. The appearance of the board is shown in the figure:

BN44-00192A Power Module Schematic can be found on this site.

This module is functionally divided into several nodes:

- Power Factor Correction (PFC) or power factor corrector (PFC);

- power supply "on duty";

- power supply "working".

Let's consider each node separately.

Power factor corrector

This assembly eliminates current harmonics in the input circuit, which are reproduced by the rectifier diodes along with the electrolytic capacitor of the switching power supply (SMPS) mains rectifier filter. These harmonic components negatively affect the power grid, so manufacturers of household appliances are required to equip their products with PFC devices. Depending on the power, these devices are active and passive. In the BN44-00192A power supply we are considering, the PFC device is active.

Here PFC is turned on by switching the voltage M_Vcc on the 8th output of the ICP801S controller simultaneously with the “working” power supply. When the standby mode is on, the active PFC does not work, since the + 311V voltage from the diode bridge through the DP801 diode is supplied to the filter capacitor. To filter harmonics at low loads, the installed input filters are quite enough. In fact, these filters are passive PFCs.

Power supply "on duty"

The standby power supply is a flyback converter circuit that is controlled by the ICB801S PWM controller. A converter operating at a fixed frequency of 55 ... 67 kHz generates a stabilized voltage of 5.2V at the output and has a current of up to 0.6A in the load. This voltage provides power to the control processor in standby mode, power to the PWM chips of the main source, as well as power to the PFC in operating mode. The TV goes from standby to operating mode by generating a voltage of 5.2V using a QB802 transistor switch. The supply voltage M_Vcc, at the same time, is supplied to the PWM controllers ICP801S and ICM801. At the same time, the PFC and the main power supply start up.

Power supply "working"

The working power supply is implemented according to the scheme of a forward converter, which is made according to a half-bridge scheme. This source generates stabilized voltages at the output:

24V (backlight inverter power), 13V, 12V and 5.3V to power the lane.

Typical malfunctions

Now consider the most popular defects of this power supply.

These include:

Liquid crystal display (LCD) indicators and displays based on light emitting diodes (LED) can be operated from conventional power supplies. However, this is not the best way to supply power. Below will be shown options for switching on using specialized microcircuits - voltage regulators, which are produced by MAXIM.

Using a digital potentiometer to adjust the LED backlight

The DS 1050 5-bit programmable potentiometer is used as the main element of the pulse-width modulator (PWM). Change the pulse width from 0 to 100% in steps of 3, 125%. The potentiometer is controlled via a two-wire serial interface compatible with I? C, addressing up to eight DS 1050s on a two-wire bus. The circuit solution for controlling the brightness of the LED backlight of the liquid crystal display is shown in fig. one.

This circuit is not designed to control the LCD contrast voltage. The 20x4 character display used in this example, type DMC 20481 from Optrex, has a yellow-green LED backlight. The forward voltage drop across the LEDs is 4.1 volts and the maximum forward current is 260mA.

By changing the duty cycle of the pulse-width modulator, thereby changing the input power to the LEDs. When the pulse is 100% of the mode cycle time, we have the maximum power supply and, accordingly, the maximum brightness of the glow. Conversely, when the cycle momentum is 0%, the brightness of the glow is also zero.

The control of the PWM modulator is quite simple. The only requirement is that the LEDs do not flash. Our eyes cannot see blinking at frequencies of 30 Hz and above. The "slowest" DS1050 operates at 1 kHz. This is quite enough for visual observation and minimization of electromagnetic radiation. The MOS transistor Q1 must be selected so that it can be directly driven by a 5V pulse width modulator whose voltage varies from ground to Vcc. The default PWM duty cycle at power-up is 2. The PWM-driven transistor Q1 can switch the 260 mA required for LED backlighting. The gate threshold voltage of transistor Q1 is 2-4 volts. Diode D1 type 1N4001 is used to lower Vcc to 4.3 volts, which is less than the maximum forward voltage drop of the LEDs. The resistor instead of the specified diode is not used due to the high power dissipation. To reliably close the MOSFET, a resistor R3 is installed, which eliminates the “floating” gate mode of Q1.

Capacitor C1 is used as a power filter, should work well at high frequency and is installed as close as possible to the terminals of U1, with a minimum distance to the power source.

Digital potentiometer DS 1050 - 001 is set by hardware with address A=000. The program for the microcontroller type 8051 can be found in the appendix to “App. note 163" on the MAXIM website.

To control the contrast of liquid crystal displays (LCDs), instead of traditional mechanical potentiometers, it is proposed to use a digital potentiometer such as DS1668/1669 Dallastats or DS 1803. The DS1668/1669 devices were chosen because they provide both push-button and microcontroller control of the current collector contact. It is also important that these devices have an internal non-volatile memory that allows you to save the position of the current collector without power supply. On fig. Figure 2 shows a schematic for LCD contrast control using a DS 1669 digital potentiometer.

Of course, a double digital potentiometer type DS 1803 can also be used here.

The liquid crystal module (LCM) is powered by 5 volts. The same voltage is supplied to the DS 1669, whose resistance is 10 kOhm. The current collector terminal is connected directly to the power input V o of the LCM driver.

The use of a digital potentiometer allows you to reduce the size of the device, significantly increase the durability and transfer control to the system microcontroller.

Well, now back to the control of the LEDs. With the increasing popularity of color liquid crystal displays in mobile phones, PDAs, digital cameras, etc., white LEDs are becoming popular light sources.

White light can be provided by either cold cathode fluorescent lamps (CCFLS) or white LEDs. Due to its size, complexity, and high cost, CCFLS has long been the only source of white. But now they are losing ground to white LEDs. They do not require high voltage (200 - 500 VAC) and a large transformer to produce this voltage. And although the forward voltage drop on a white LED (3 to 4V) is higher than on a red (1.8V) or green (2.2 - 2.4V), they still require fairly simple power supplies. The brightness of a white LED is controlled by changing the current flowing through it. Full brightness occurs at 20 mA. As the current flowing through the LED decreases, the brightness decreases. Digital cameras and mobile phones typically require 2 to 3 LEDs. There can be 2 ways to group LEDs: parallel and serial. When the LEDs are connected in series, the current through each will be guaranteed to be the same. But such an inclusion requires a higher voltage than with parallel connection. When connected in parallel, the voltage is approximately equal to the forward voltage drop across a single LED instead of the voltage drop across the entire row of LEDs. However, the brightness of the diodes can be different due to the spread of the forward voltage drop across the LEDs, hence different currents, if they are not regulated. The battery voltage in most cases is not enough to light up the white LED, so a DC/DC converter must be used. In this case, the parallel connection of LEDs is desirable, since DC / DC converters are most effective with a small ratio of increased output voltage to input voltage.

Parallel connection of LEDs

There are three main ways to connect LEDs in parallel, as shown in fig. 3.

1. Independent current regulation through each diode.
2. The currents are regulated by ballast resistors from a voltage regulated source corresponding to the forward voltage drop across the LED.
3. From a source with adjustable current, a voltage is obtained equal to the voltage drop across the adjustable LED and resistor, and with the help of ballast resistors, the current through the remaining LEDs is regulated.

Let's take a closer look at these inclusion options.

A simple way to control the current flowing through the LEDs is to use a chip specially designed for this purpose. The switching circuit is shown in fig. 4. Shown here is a cheap MAX1916 chip that allows you to adjust the current through 3 white LEDs. The absolute accuracy of the current is 10%, and the currents flowing through the LEDs differ by no more than 0.3%. This is the most important characteristic, since the luminous flux from each LED must be the same. At full brightness, the current through the LED is 20 mA. In this case, 225 mV is enough, exceeding the voltage drop across the LEDs, for the microcircuit to maintain the set current value. Setting the current through the LEDs is done using the resistor R set . The equation for calculating the current is as follows.




where:
I led - current flowing through the LED
230 - chip conversion factor
U out - output voltage of the regulator
U set = 1, 215 V
R set is a resistor installed between the regulator output and the SET MAX1916 input (kΩ).




The absolute current must also be controlled, but the brightness will change in general for the entire device (for example, a phone display). The change in brightness can be obtained by applying to the enable (EN) input of the chip with a pulse-width modulation signal. The maximum brightness will be at 100% pulse width, and at 0% - the LED does not shine.

Using a power supply with regulated output voltage.

This switching method is less accurate, since the individual currents through each LED are not regulated. How can one increase the absolute accuracy of the currents flowing and matching them through each diode?

The current through the LED is calculated by the formula:

Iled \u003d (V out - V d) / R

Due to production variations, even at the same currents, the forward voltage drop across the LED (V d) can be different. You can write the ratio of two currents through 2 diodes

I1/I2 = R2/R1 [(V out - V d1)/(V out - V d2)]

Taking into account that the resistors have high accuracy (this is acceptable), we have:

I1/I2 = (V out - V d1)/(V out - V d2)

It follows that the ratio (difference) of the currents through the diodes is the smaller, the higher the output voltage of the power source. It must be borne in mind that the convergence of the values ​​\u200b\u200bof the currents through the LEDs is paid for by a higher power consumption. Therefore, we can recommend a voltage at the output of the regulator equal to 5 volts.

To obtain this voltage, you can use simple converters such as MAX 1595 (U out = 5V, I out = 125 mA), or use converters MAX1759 with regulated output. Thus, by changing the output voltage of the regulator, it is possible to correct the currents in the LEDs to the desired level (for example, 20 mA). If it is not possible to correct the current by adjusting the voltage at the output of the power supply, then resistors and MOS transistors are placed in parallel with the ballast resistors R1a: R3a, as shown in Fig. 5. Turning the MOS transistors on and off with a logic level, you can connect or disconnect additional resistors R1v:.R3v, effectively changing the value of the ballast resistor.




1. Using a converter with adjustable output current. On fig. 3c shows the principle of using a variable output current converter. In this scenario, the current through one of the diodes (fig. 3c - D1) is converted into a voltage drop across the resistor R1 and it is this voltage that is maintained by the converter. The converter can be a key type, switched capacitors or a linear regulator.

   The equation for the current through the LED is the same as above.

   I x \u003d (V out - V dx) / R x (1)

   But in this case, V out is not adjustable, but I1 is adjustable and its value is

   I1 = V o.c / R1 (2)

   where: V o.c is the feedback voltage taken from the resistor R1.

   Since the current of only one diode is regulated, the different forward voltage drops across the LEDs can cause different currents to flow through them. In this case, you can use the following. We divide the resistor into 2 parts: R1 \u003d R1A + R1B and substitute it in equation (1), and replace the value of R1 in equation (2) with R1B. R2 and R3 do not require resistor splitting. Their values ​​must be equal to R1A + R1B. Now the output of the regulator will maintain a voltage determined by the voltage drop across the resistor R1B, as shown in fig. 6. If the setting from R1B is equal to the voltage of R1, then the error amplifier will remain in the same state, the output voltage of the regulator will increase, which will ensure the matching of the currents through each LED.

   
   

Sequencing LEDs

The main advantage of connecting LEDs in a series chain is that the same current flows through all the diodes and the brightness of the glow is the same. The disadvantage with this inclusion: a higher voltage is required, since the voltage drop on each LED is summed up. Even 3 white LEDs require 9 - 12 volts. Usually, key regulators are used for such inclusion, as the most effective converters for these purposes. Figure 7 shows the connection diagram of the MAX 1848 key regulator, designed to control three white LEDs connected in series. The device can be powered from 2.6 to 5.5 volts with an output voltage of up to 13 volts. The input range is designed for one Li-ion battery or 3 NiCD/NiMH batteries. The operating frequency of the regulator is 1.2 MHz, which allows the use of external components with minimal dimensions. The output is a PWM signal. The excess voltage is rectified and fed to the LEDs. The current through the LEDs, and thus the brightness, can be adjusted using either a DAC-sampled voltage or a filtered PWM signal applied to the CTRL input of the MAX 1848. The MAX 1848 is up to 87% efficient with LEDs.

For large displays where many LEDs are required, the MAX 1698 key controller can be used (see Figure 8). The microcircuit can operate from an input voltage of only 0.8 Volts, and the output voltage is limited by the operating voltage of the external n-channel MOS transistor. Low, up to 300 mV feedback voltage (FB pin) contributes to the maximum efficiency of the circuit, which reaches 90%. The brightness of the LED is adjusted using a potentiometer, in which the brush is connected to the ADJ pin of the microcircuit. The potentiometer can be used both analog and digital.

Of course, the number of chips that are used to power and backlight liquid crystal and LED displays is not limited to the names presented in the article. If the reader wants to pick up the microcircuits necessary for his particular case, then there is nothing easier than to enter the site

Here are the TOP 10 most common malfunctions of LCD monitors that I felt the hard way. The rating of malfunctions was compiled according to the personal opinion of the author, based on experience in a service center. You can think of this as a universal repair guide for almost any LCD monitor from Samsung, LG, BENQ, HP, Acer and others. Here we go.

I divided LCD monitor malfunctions into 10 points, but this does not mean that there are only 10 of them - there are many more, including combined and floating ones. Many of the breakdowns of LCD monitors can be repaired with your own hands and at home.

1st place - the monitor does not turn on

generally, although the power indicator may flash. At the same time, the monitor lights up for a second and goes out, turns on and immediately turns off. At the same time, cable jerking, dancing with a tambourine and other pranks do not help. Tapping the monitor with a nervous hand usually doesn't work either, so don't even try. The reason for such a malfunction of LCD monitors is most often the failure of the power supply board, if it is built into the monitor.

Recently, monitors with an external power source have become fashionable. This is good, because the user can simply change the power supply in case of a breakdown. If there is no external power source, then you will have to disassemble the monitor and look for a malfunction on the board. in most cases it is not difficult, but you need to remember about safety.

Before you fix the poor fellow, let him stand for 10 minutes, unplugged. During this time, the high-voltage capacitor will have time to discharge. ATTENTION! DANGER TO LIFE if the PWM transistor is also burned out! In this case, the high-voltage capacitor will not discharge in an acceptable time.

Therefore, ALL before repair, check the voltage on it! If a dangerous voltage remains, then you need to manually discharge the capacitor through an insulated one of about 10 kOhm for 10 seconds. If you suddenly decide to close the conclusions, then take care of your eyes from sparks!

Next, we proceed to inspect the monitor power supply board and change all burnt parts - these are usually swollen capacitors, blown fuses, transistors and other elements. It is also MANDATORY to solder the board or at least examine the soldering under a microscope for microcracks.

From my own experience I will say - if the monitor is more than 2 years old - then 90% that there will be microcracks in the soldering, especially for LG, BenQ, Acer and Samsung monitors. The cheaper the monitor, the worse it is made at the factory. Up to the point that they do not wash out the active flux - which leads to the failure of the monitor after a year or two. Yes, just as the warranty expires.

2nd place - the image flashes or goes out

when the monitor is turned on. This miracle directly indicates to us a malfunction of the power supply.

Of course, the first step is to check the power and signal cables - they must be securely fastened in the connectors. A flashing image on the monitor tells us that the monitor's backlight voltage source is constantly jumping off the operating mode.

3rd place - spontaneously turns off

after the time has elapsed or does not turn on immediately. In this case, there are again three common malfunctions of LCD monitors in order of frequency of occurrence - swollen electrolytes, microcracks in the board, a faulty microcircuit.

With this malfunction, a high-frequency squeak from the backlight transformer can also be heard. It usually operates at frequencies between 30 and 150 kHz. If its mode of operation is violated, oscillations can occur in the audible frequency range.

4th place - no backlight,

but the image is viewed under bright light. This immediately tells us about the malfunction of LCD monitors in terms of backlighting. In terms of frequency of appearance, one could put it in third place, but it is already taken there.

There are two options - either the power supply and inverter board burned out, or the backlight lamps are faulty. The latter reason is not often found in modern monitors. If the LEDs are in the backlight and fail, then only in groups.

In this case, there may be a darkening of the image in places at the edges of the monitor. It is better to start repairs with diagnostics of the power supply and inverter. The inverter is the part of the board that is responsible for generating a high-voltage voltage of the order of 1000 volts to power the lamps, so in no case do not try to repair the monitor under voltage. You can read about it on my blog.

Most monitors are similar in design, so there shouldn't be any problems. At one time, monitors simply fell down with a broken contact near the tip of the backlight. This is treated by the most careful disassembly of the matrix in order to get to the end of the lamp and solder the high-voltage wiring.

An easier way out of this unpleasant situation can be found if your friend-brother-matchmaker has the same monitor lying around, but with faulty electronics. Blinding from two monitors of similar series and the same diagonal will not be difficult.

Sometimes even a power supply from a larger diagonal monitor can be adapted for a smaller diagonal monitor, but such experiments are risky and I do not advise starting a fire at home. Here in someone else's villa - this is another matter ...

6th place - spots or horizontal stripes

Their presence means that the day before you or your relatives had a fight with the monitor because of something outrageous.

Unfortunately, household LCD monitors do not provide shockproof coatings and anyone can offend the weak. Yes, any decent poke with a sharp or blunt object will make you regret it.

Even if there is a small trace or even one broken pixel, the spot will still grow over time under the influence of temperature and voltage applied to liquid crystals. Unfortunately, it will not work to restore the broken pixels of the monitor.

7th place - no image, but backlight is present

That is, a white or gray screen on the face. First you should check the cables and try connecting the monitor to a different video source. Also check if the monitor menu appears on the screen.

If everything remains the same, look carefully at the power supply board. In the power supply of the LCD monitor, voltages of 24, 12, 5, 3.3 and 2.5 Volts are usually formed. You need to check with a voltmeter if everything is in order with them.

If everything is in order, then we carefully look at the video signal processing board - it is usually smaller than the power supply board. It has a microcontroller and auxiliary elements. You need to check if they are getting food. With one touch the contact of the common wire (usually along the circuit of the board), and with the other go over the pins of the microcircuits. Usually food is somewhere in the corner.

If everything is in order in terms of power, but there is no oscilloscope, then we check all the monitor cables. on their contacts. If you find something, clean it with isopropyl alcohol. In extreme cases, you can clean it with a needle or scalpel. Also check the board with the monitor control buttons.

If all else fails, then you may have encountered a case of a flashed firmware or a microcontroller failure. This usually happens from surges in the 220 V network or simply from the aging of the elements. Usually in such cases you have to study special forums, but it's easier to use it for spare parts, especially if you have a familiar karateka in mind who fights against objectionable LCD monitors.

8th place - does not respond to control buttons

This case is easily treated - you need to remove the frame or the back cover of the monitor and pull out the board. Most often there you will see a crack in the board or soldering.

Sometimes there are faulty or. A crack in the board violates the integrity of the conductors, so they need to be cleaned and soldered, and the board glued to strengthen the structure.

9th place - reduced monitor brightness

This is due to the aging of the backlights. According to my data, LED backlighting does not suffer from this. It is also possible that the performance of the inverter may deteriorate, again due to the aging of the constituent components.

10th place - noise, moiré and image jitter

Often this happens due to a bad VGA cable without an EMI suppressor -. If changing the cable does not help, then power interference may have entered the imaging circuits.

Usually, they are eliminated by circuitry using filter capacitances for power supply on the signal board. Try to replace them and write me about the result.

This concludes my wonderful rating of the TOP 10 most common LCD monitor malfunctions. Most of the data on breakdowns is collected based on the repairs of such popular monitors as Samsung, LG, BENQ, Acer, ViewSonic and Hewlett-Packard.

This rating, it seems to me, is also valid for and . What is your situation on the LCD monitor repair front? Write on and in the comments.

Yours sincerely, Pike Master.

P.S.: How to disassemble the monitor and TV (how to snap off the frame)

The most common questions when disassembling LCD monitors and TVs are how to remove the frame? How to release latches? How to remove the plastic housing? etc.

One of the craftsmen made a nice animation explaining how to disengage the latches from the body, so I'll leave it here - it will come in handy.

To view animation- click on the image.