Samsung Syncmaster 740n Dies Screen Backlight

I bring the TOP 10 most common LCD monitor malfunctions that I felt in my own skin. The rating of malfunctions is compiled in the personal opinion of the author, based on experience in the service center. You can take this as a universal repair guide for almost any LCD monitor from Samsung, LG, BENQ, HP, Acer and others. Here we go.

I divided the malfunctions of the LCD monitors into 10 points, but this does not mean that there are only 10 of them. there are a lot more of them, 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

in general, although the power indicator may blink. In this case, the monitor lights up for a second and goes out, turns on and immediately turns off. At the same time, cable juggling, dancing with a tambourine and other pranks do not help. The method of tapping the monitor with a nervous hand usually does not help either, so do not 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 supply have become fashionable. This is good, because the user can simply change the power source in case of a breakdown. If there is no external power supply, you will have to disassemble the monitor and look for a malfunction on the board. It is not difficult to disassemble the LCD monitor in most cases, but you need to remember safety precautions.

Before fixing the poor fellow, let him stand for 10 minutes, disconnected from the network. During this time, the high-voltage capacitor has time to discharge. ATTENTION! DANGER FOR LIFE if the diode bridge and the PWM transistor burned out! In this case, the high voltage capacitor will not be discharged in an acceptable time.

Therefore, ALL before repairing check the voltage on it! If the hazardous voltage remains, then you need to discharge the capacitor manually through an insulated resistor of about 10 kOhm for 10 seconds. If you suddenly decided to close the terminals with a screwdriver, then take care of your eyes from sparks!

Samsung Syncmaster 740n Dies Screen Backlight

Next, we proceed to inspect the board of the monitor power supply and change all the 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 the microscope for microcracks.

From my own experience I’ll say that if the monitor is more than 2 years old, then 90% that there will be microcracks in 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 the active flux is not washed out. which leads to the failure of the monitor after a year or two. Yes, yes, just when the warranty ends.

2nd place. the image blinks or goes out

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

Of course, the first thing you need to check the power and signal cables. they must be securely attached to the connectors. The blinking image on the monitor tells us that the voltage source of the monitor backlight constantly jumps from the operating mode.

The most common cause is bloated electrolytic capacitors, soldered microcracks and a faulty TL431 chip. Inflated capacitors most often cost 820 μF 16 V, they can be replaced with a larger capacitance and higher voltage, for example, the cheapest and most reliable ones are Rubycon 1000 μF 25 V capacitors and Nippon 1500 μF 16 V capacitors. There are cheaper ones from decent (but necessary 105 degrees) Nichicon 1000 uF 25 V. Everything else from China will not last long.

Samsung Syncmaster 740n Dies Screen Backlight

3rd place. spontaneously shuts down

after a period of time or does not turn on immediately. In this case, again, three frequent malfunctions of LCD monitors in order of frequency of occurrence. swollen electrolytes, microcracks in the board, faulty TL431 chip.

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

Samsung Syncmaster 740n Dies Screen Backlight

4th place. no backlight,

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

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There are two options. either the power supply and inverter board burned out, or the backlight is faulty. The last reason in modern monitors with LED backlight LED is not common. If the LEDs are backlit and fail, then only in groups.

In this case, darkening of the image in places along the edges of the monitor may be observed. It is better to start the repair with the 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 about 1000 volts to power the lamps, so in no case do not bother to repair the monitor under voltage. You can read about repairing the Samsung monitor power supply on my blog.

Most monitors are similar in design, so there should be no problems. At one time, monitors simply fell in contact with the tip of the backlight. This is treated with the most accurate disassembly of the matrix to get to the end of the lamp and solder the high voltage wiring.

If the backlight itself burns out, I would advise replacing it with an LED backlight line, which usually comes with its inverter. If you still have questions. write to me in the mail or in the comments.

Video: Samsung Syncmaster 740n Dies Screen Backlight


Samsung Syncmaster 740n Dies Screen Backlight

5th place. vertical stripes in the image

These are the most nasty malfunctions of LCD monitors in the life of any computer technician and user, because they tell us that it is time to buy a new LCD monitor.

Why new to buy? Because the matrix of your pet 90% has become unusable. Vertical stripes appear when the signal loop contacts with the contacts of the matrix electrodes.

This can only be treated by carefully applying adhesive tape with anisotropic adhesive. Without this anisotropic glue, I had a bad experience repairing a Samsung LCD TV with vertical stripes. You can also read how the Chinese repair such strips on their machines.

A simpler way out of this unpleasant situation can be found if your friend, brother-in-law, has the same monitor, but with faulty electronics. Blind of two monitors of similar series and the same diagonal of labor is not difficult.

Sometimes even the power supply from a monitor with a larger diagonal can be adapted for a monitor with a smaller diagonal, but such experiments are risky and I do not recommend starting a fire at home. But in a strange 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 into the matrix of the LCD monitor will make you regret it.

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

Samsung Syncmaster 740n Dies Screen Backlight

7th place. no image, but there is a backlight

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

If everything remains as before, we look carefully at the power supply board. In the power supply unit of the LCD monitor, voltages of 24, 12, 5, 3.3 and 2.5 volts are usually formed. It is necessary to check with a voltmeter whether everything is in order with them.

If everything is in order, then we carefully look at the video processing board. it is usually smaller than the power supply board. It has a microcontroller and auxiliary elements. It is necessary to check whether food comes to them. With one probe, touch the contact of the common wire (usually along the circuit of the board), and with the other go through the terminals of the microcircuits. Usually food is somewhere in the corner.

If the power supply is OK, but the oscilloscope is not there, then we check all the monitor loops. Their contacts should not be soot or dark. If you find something. clean with isopropyl alcohol. In extreme cases, you can clean it with a needle or a scalpel. Also check the cable and the board with the monitor control buttons.

If all else fails, then perhaps you are faced with a case of flashing firmware or a malfunctioning microcontroller. This usually happens from surges in a 220 V network or simply from aging elements. Usually in such cases you have to study special forums, but it’s easier to put them into spare parts, especially if you have a familiar karate, fighting against objectionable LCD monitors.

Samsung Syncmaster 740n Dies Screen Backlight

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 with buttons. Most often there you will see a crack in the board or in solder.

Sometimes there are faulty buttons or a loop. 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. low monitor brightness

This is due to the aging of the backlight. According to my data, LED backlighting does not suffer from this. It is also possible the deterioration of the parameters of the inverter, again due to the aging of the components.

Samsung Syncmaster 740n Dies Screen Backlight

10th place. noise, moire and jitter

Often this happens due to a bad VGA cable without an electromagnetic interference suppressor. a ferrite ring. If replacing the cable did not help, then it is possible that a power jam has entered the imaging circuit.

Usually they are disposed of schematically using filtering capacities for power on the signal board. Try replacing them and write to me about the result.

On this my wonderful rating of the TOP 10 most common LCD monitor malfunctions is over. The main part of the data on breakdowns is collected on the basis of repairs of such popular monitors as Samsung, LG, BENQ, Acer, ViewSonic and Hewlett-Packard.

This rating, it seems to me, is also true for LCD TVs and laptops. And what is your situation at the front of repair of LCD monitors? Write on the forum and in the comments.

Regards, Soldering Master.

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

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

One of the masters made a good animation explaining how to disengage the latches from the housing, so I will leave it here. it will come in handy.

To view animation. click on the image.

Samsung Syncmaster 740n Dies Screen Backlight

P.P.S.: Power supplies and common LCD monitor malfunctions

Recently, manufacturers of monitors are increasingly equipped with new monitors external plastic case power supplies. I must say that this facilitates the troubleshooting of LCD monitors by replacing the power supply. But it complicates the mode of operation and repair of the power supply itself. they often overheat.

How to disassemble such a case, I showed below in the video. The method is not the best, but fast and can be done using improvised means.

DIY LCD monitor repair

A common malfunction is when the LCD monitor lights up for a second and goes out. What to do in this case and how to use this TOP fault.

Everything is simple. To repair the LCD monitor, follow these steps:

  • Step 1. Disconnect the monitor from the 220 V network and from the computer and decide. we will repair it ourselves or take it to the diagnostic service for inexpensive.
  • Step 2. If you decide to understand it yourself, then take the tools: screwdrivers, a knife or a scalpel and a soft base to lay the monitor down with the matrix.
  • Step 3. Disassemble the LCD display, observing safety precautions and remembering the latches. How they open is shown above in the animation.
  • Step 4 Discharge the high voltage capacitor. It is necessary! Especially if you want to get to a positive repair result.
  • Step 5. Inspect the board for swollen capacitors, burnt transistors and microcracks.
  • Step 6. If there are any finds in Step 5, replace the burned-out, dissolve the cracked one.
  • Step 7. Check the monitor’s performance, observing safety precautions. If everything is in order, then go to Step 10.
  • Step 8. Take a multimeter and ring the fuses, diode bridge, transformers and transistors. Replace burned radio elements.
  • Step 9. Check the operation of the LCD monitor. If the monitor continues to blink, then check the voltage at the test points on the board. This requires knowledge of circuitry, as well as a service manual with an ideal circuit. Further actions are difficult to describe in general terms. Here begins the creative process of the Repair Wizard. For discussion, write in the comments or contact our forum.
  • Step 10. In the event of a successful repair of the blinking LCD monitor with your own hands, make a test run for 2-3 hours in the disassembled state. After that, the monitor can be assembled and operated.

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