Home Windows Vista Analysis of the lg flatron monitor. Projectors and monitors. It is better not to touch the display glass. Very fragile

Analysis of the lg flatron monitor. Projectors and monitors. It is better not to touch the display glass. Very fragile

How to disassemble an LG monitor

Do-it-yourself disassembly of the LG FLATRON L1734S-BN monitor

I'll briefly tell you what we will do:

1.Remove the monitor stand

2. Separate the halves of the body from each other

3.Disconnect the control panel

4.Disconnect the backlight lamp connectors

5.Disconnect the cable from the matrix

6.Remove the power board

So, to disassemble the monitor we need:

Screwdriver-
Screwdriver+
Box for screws
Substrate or newspaper

Note

When you use a flat screwdriver to separate the halves of the case from each other, try to do it carefully, since using a flat screwdriver when separating it can damage appearance monitor!

Let's disassemble the monitor:

Before starting work, lay a newspaper or pad on the table.

1.Unfold the latches and remove the monitor stand
2. Take a flat-head screwdriver in your hands, insert the tip between the halves, pull the screwdriver toward you along this gap, when you encounter a latch on the way, then slightly pull the plastic of the back cover up and at the same time slightly turn the screwdriver along the axis until the latch opens.

3.Unfold the latches and remove the control panel

4. Move the front half of the monitor aside 5. Unscrew the 3 screws and remove the leg

6.Remove the plastic cover

7.Unscrew the 4 screws and remove the monitor stand mounts

8. Unscrew 1 screw on the left side

9.Unscrew in the same way right side 1 screw

10. Disconnect the connectors of the backlight lamps

11.Disconnect the cable from the matrix

12.Unscrew the 4 screws on the power board

13.Disconnect the cable from the video board

14.Disconnect power from the video card

15.Remove the power board

This concludes our analysis of the LG flatron l1734s-bn monitor!

Best regards Nako!

mynako.ru

Easy repair of LG FLATRON L1753S monitor

Hi all. Continuing the topic of repairs for novice craftsmen, I suggest your light for attention LG FLATRON L1753S monitor repair. This monitor showed no signs of life at all, but repairing it does not require any deep knowledge in electronics, and most importantly, only care and accuracy are required.

Disassembling the monitor.

The most labor-intensive process of repairing these monitors is their disassembly. Sometimes it can be very difficult to disconnect the latches, especially without spoiling the appearance of the monitor, but with experience this procedure becomes much easier.

First of all, I unscrewed the four bolts on the back cover of the monitor.

bolts on the back of the monitor

Next, I put the monitor down and started removing the front frame. To do this, I first snapped the frame in the center on 4 sides. Next comes the most difficult part, namely separating the corners of the monitor. To do this, I used an old plastic card, inserted it into the gap between the panels, and carefully snapped the panel off.

Having removed the frame, he slowly lifted the matrix, and then turned off the keyboard.

Turning off the monitor lamps

I immediately turned them off, and then lifted the compartment with the boards to disconnect the cable from the monitor matrix.

Disabling the monitor matrix cable

Fault identification and repair.

Taking the board in hand, I immediately saw 3 swollen capacitors.

swollen electrolytic capacitors

These are 1000/25v, 1000/16v and 680/25v. Before replacing the capacitors, I measured the voltage at the input from the power supply, it was 8.5 instead of 12V, and 1.1 instead of 5 volts. I didn’t take pictures of the measurements, it was a little distracting. Having replaced the capacitors, the output voltages stabilized, although instead of 12V the voltage was 14V, but without load this is within normal limits.

Measured 5 volts

Measured 12 volts

After assembly, the monitor worked.

result of repair

Thank you for your attention. Good luck with the repairs.

All the tools and consumables that I use in repairs are located here. If you have any questions about TV equipment repair, you can ask them on our new forum.

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PostsLG FLATRON L1753SReplacementCapacitorsRepair

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How I fixed a burnt-out monitor | Digital Chip - Digital devices

Damn, what an ambush... I came home from work today, turned on the computer, and went to change clothes. It started to start up, beeped, buzzed, and crackled. But for some reason the monitor did not turn on. I him this way and that way. Dead. Completely. Even in his hearts he hit him... 🙁 (didn’t help, by the way)

He has worked for me for probably six years, maybe even seven. Apparently it's time for him to die. Crap. What a bad time. I'll have to go get a new monitor. Well, this will only work for the weekend. Today I’ll try to pick this one up.

My monitor is the most ordinary one, bought a long time ago for 6 and a half thousand “everwooden” ones, I don’t remember exactly. It's called LG FlatronL1953S. He doesn't have any special qualities. Just an ordinary workhorse. It looks like this:

LG Flatron L1953s monitor in person

The patient was examined and no signs of life were found. Let's start opening:

Let's start disassembling

The four screws came out very quickly. It's time to remove the back cover. But it, the back cover, is not held on by screws, but is attached together with the front frame with latches.

Opening the monitor frame

Well, it’s a hassle to separate them. You're afraid you might break the latches. And there are so many of them around the perimeter... You have to use all available means and devices.

Tools for opening plastic latches

But “the one who walks will master the road.” “It’s long or short,” but we won. The patient is opened! Separated the back cover from the front frame:

Opened the back cover

So, let's see what we have here. The entire metal protective casing that covers the boards is attached to tape. Nothing, not a single screw, not a single latch.

All rear end held on with tape

The guts of the monitor are not rich in variety and consist of two boards: a power supply board and a control board.

Guts of the monitor - control board and power supply

Let's start with nutrition. We pick out the power supply board. Well, there’s dust on it (I’ve never vacuumed the monitor since I bought it).

Dusty power supply board

Blow/wipe/vacuum the dust from the board. And here she is in person in all her glory:

Personal power supply

We carefully inspect the board. First of all, let's check the fuses. There is only one on the board. It works. Let's look further.

Suspicious Conders

So, sir, what is this? And these are awesomely suspicious, swollen, electrolytic capacitors. Let's take a closer look.

Swollen capacitors

Well, the most likely cause of death of the monitor is these electrolytes. We are looking for a replacement. I looked through all my radio-electronic junk, but didn’t immediately find the necessary electrolytes. I had to be smart.

In the end this is what happened:

Yes, I was lucky that I found a large gray Conder, still made in the Soviet Union, from God knows what shaggy year. I'm not at all sure if it's working. But there is no way out, there is no other Conder that is close in parameters. I'll have to install it. Here's what happened:

Resoldered capacitors

I don’t know whether this large aluminum cap of the capacitor is connected to the positive or negative contact, so I just put insulation from a piece of electrical tape (I should have rung it with a tester... hmm...). In general, the final board looks like this:

Repaired board

I put everything together and turned it on. Everything worked. It turns out that the patient's death was clinical and not complete. Very very best!!! The trip to buy a new monitor is postponed indefinitely.

This is the reason for the breakdown!

Well, and finally, a video with the process of picking the insides of a patient.

Sorry for the rambling speech. I came home from work, my head just can’t cook... :)

By the way, I talked about transformers in the video - it’s about here.

It is no secret that owners of LCD monitors often encounter breakdowns of these devices. In many cases, you can repair a faulty device yourself.

Let's look at an example of several steps with which you need to start repairs. LCD monitor and a computer.

Disassembling an LCD monitor is a rather troublesome operation and can be more time-consuming than eliminating the cause of the breakdown itself.

To disassemble an LCD monitor - in this case, the ACER AL1716 model - you need to place it with the screen on a flat surface, and place a soft cloth or other material directly under the LCD screen that will protect its surface from scratches.

Attaching the stand to the chassis

After the stand is disconnected from the main body, using a sharp knife blade or other sharp tool, we snap off the plastic latches that hold the front and back parts of the case together. This operation is quite labor-intensive and you need to be careful, since a sharp blade can damage the appearance of the case and break the latches.

In order to gain access to the control and power printed circuit boards, you need to disconnect the metal frame with the LCD panel from the back of the plastic case. To do this, you need to bend the latches of the four latches on the sides of the plastic panel. After this, the main frame with electronic filling can be easily removed and disassembly can continue.

Locks for the rear of the case and the main unit

Once the back cover of the plastic case is removed, we will see that the LCD monitor itself is a metal frame on which three electronic printed circuit boards and an LCD panel are mounted. All printed circuit boards are covered with metal covers to reduce electromagnetic radiation. Radiation from high-frequency circuits can affect the normal operation of other electronic devices, so all electronics are hidden under a metal cover.

Main metal frame with electronic filling

Structurally, a computer LCD monitor consists of several printed circuit boards and electronic components, namely:

Liquid crystal display (LCD) panel.

Power supply and inverter for powering backlight lamps.

VGA control and interface board.

Keypad with operating mode indicator.

These are the main electronic components that we will find during disassembly.

Next, unscrew the four bolts that secure the LCD panel to the frame. Attention! The LCD panel is connected to other boards through several wires and multi-core cables. Namely, the panel has two wires with four connectors. These are connectors for connecting backlight lamps to the inverter board. They need to be disconnected. The easiest way to do this is with tweezers.

The LCD panel is also connected to the control board via a multi-core flexible cable. It is better to disconnect it from the control board side, because it is fixed quite rigidly on the LCD panel board, and it is not advisable to touch it.

LCD panel

When the LCD panel is detached from the main frame, access to the control and power boards, which are located in a niche in the metal base, opens.

Printed circuit boards for power supply and control

My monitor is the most ordinary one, bought a long time ago for 6 and a half thousand “everwooden” ones, I don’t remember exactly. Called LG FlatronL1953S. He doesn't have any special qualities. Just an ordinary workhorse. It looks like this:

The patient was examined and no signs of life were found. Let's start opening:

The four screws came out very quickly. It's time to remove the back cover. But it, the back cover, is not held on by screws, but is attached together with the front frame with latches.

Well, it’s a hassle to separate them. You're afraid you might break the latches. And there are so many of them around the perimeter... You have to use all available means and devices.

But “the one who walks will master the road.” “It’s long or short,” but we won. The patient is opened! Separated the back cover from the front frame:

So, let's see what we have here. The entire metal protective casing that covers the boards is attached to tape. Nothing, not a single screw, not a single latch.

The guts of the monitor are not rich in variety and consist of two boards: a power supply board and a control board.

Guts of the monitor - control board and power supply

Let's start with nutrition. We pick out the power supply board. Well, there’s dust on it (I’ve never vacuumed the monitor since I bought it).

Blow/wipe/vacuum the dust from the board. And here she is in person in all her glory:

We carefully inspect the board. First of all, let's check the fuses. There is only one on the board. It works. Let's look further.

So, sir, what is this? And these are awesomely suspicious, swollen, electrolytic capacitors. Let's take a closer look.

Well, the most likely cause of the death of the monitor is these electrolytes. We are looking for a replacement. I looked through all my radio-electronic junk, but didn’t immediately find the necessary electrolytes. I had to be smart.

In the end this is what happened:

This is the cause of the breakdown!

Well, and finally, a video with the process of picking the insides of a patient.

Sorry for the rambling speech. I came home from work, my head just can’t cook... :)

By the way, I talked about transformers in the video - this is about .

The LG flatron W1942S – SF January 2008 monitor shows no signs of life and does not turn on. Turned it off and didn't turn on again.

Let's disassemble. We start approximately 1/3 from the edge from the bottom. We press the back cover inward, the front outward. It is better to use plastic cards and several flat strips or screwdrivers.

Note the double latches on the silver frame. You cannot bend the black part too far down (or vice versa, the silver part) as the latch will break on the side of the black part. Therefore, we put plates where there are none.

At the edges of the latches on the LG flatron W1942S they look like this

Well, a little skill and everything will work out. It is better to disfigure the black part, because... The scratches are not so noticeable later.

A classic of the genre, we change the capacitors on the LG W1942S - SF. They are swollen to make it easier to find.

These are the instigators of trouble 47omk35v 105 degrees WITH

The parameters of these capacitors are not suitable ESR became 3.3 Ohm, should be less than 0.1 Ohm

This is an ordinary new Chinese capacitor (Extra “E-C” class) ESR is overestimated by 1.5 - 2 times.

It will work, but may cause heating of the capacitor and transistor of the pulse converter.

We install capacitors of a normal brand (Jamicon, Suntan, Samwha, Yageo).

They changed it, but it was too late. You may be lucky and the monitor will work, but our transistor assembly has already been broken. I needed .

The transistor wiring (according to the inverter circuit for the monitor backlight) was not damaged, all parts turned out to be working.

All that remains is to purchase the TO252-4 case or analogues STU407D, AR4525GEH, IRF7389, IRF7319PBF (worse in current). I put STU407D, because The current characteristics are almost 2 times better.

I soldered more tin onto the assembly and pad for good heat transfer.

Everything worked for me. You also need to check the temperature of the transducers and the temperature of the capacitors every minute in the first 10 minutes. If they are not hot, then we check the temperature every five minutes.

LG W1942S backlights do not turn on - APM4048DU4 is to blame

If the repair did not end with resoldering the capacitors, and the LG flatron W1942S - SF apparently does not have protection triggered after a capacitor leak (they need to be changed in advance), then everything may turn out to be more complicated. Short circuit of the trances in the inverter or the trance legs are missing in the transformer itself, then search for “inverter circuit for monitor backlighting”.

Monitor repair | Experimental

Sometimes it seems that modern electrical appliances are designed to break down soon after the warranty period expires.

Meet our LG W2452V. He is six years old. About two years after purchase, it began to have problems resuming from standby mode. We opened it up and found two leaking capacitors on the 5V rail, as well as several swollen capacitors on the 24V rail. We only replaced the 5V capacitors, since we did not have the correct parts to replace the others. After assembly, the monitor worked fine for several months, but then problems with waking up appeared again. I had to open the monitor again and this time complete the work.

In general, the problem with the failure of capacitors on power circuits is quite typical for consumer electronics. It is often possible to understand that they are to blame by the deteriorating stability of operation and the emerging sensitivity to the quality of power from the network. There are other symptoms, including complete failure to work. But it will be possible to say for sure only after the autopsy, which will be discussed further in detail and in all details.

Monitor repair | Removing the frame

Removing the frame requires a lot of patience, dexterity and strength. The bezel latches hold the LCD panel into the case, so you need to be careful with them. We used a discount plastic card as a wedge.

The plastic of this card is quite soft, so cosmetic damage is kept to a minimum. But after assembly, you will have to wipe off the adhesive plastic residue that comes off the card.

Monitor repair | Losses

If you are lucky and all the latches remain in place, you will see the picture on the left (the latches will withstand one more assembly). Otherwise, you will see the result as in the photo on the right - here some of the latches have broken off. The hardest part is with the corners. At this point, three panels meet perpendicularly, which significantly increases rigidity.

There were 20 latches throughout the frame. We broke three of the four in the corners. Moreover, the first two broke during the first repair. But this is for this model. With other monitors everything may work out more successfully.

Monitor repair | Behind the frame

In addition to its cosmetic function, the frame contains a power button, latch holes on the bottom, and design clips to ensure the LCD panel doesn't accidentally fall out. If you break too many latches, you will have to use electrical tape.

Monitor repair | Turning it over

After removing the bezel, we flipped the case over and the LCD panel simply fell out. If you don't want to damage it, don't forget to hold it with your fingers. You also need to find the cables that need to be disconnected. For example, in our photo you can see the audio cable and the wire for the power button.

Monitor repair | Back cover from inside

After removing the LCD panel and electronics board, we were left with an almost bare back cover. All that remains are the adjustment, power and PCB with headphone jack.

Considering that the panel makes up about half of the total weight of the monitor, the case could use additional stiffening reinforcements around the mounting point of the latch and on the back cover itself. In the end, it took us about ten seconds to remove the panel with some gentle pushing. Our other screen, the Dell, gave way in one second. Most likely, the lighter weight thanks to the LED backlight helped.

Monitor repair | Audio card

Apparently, the audio card with a 3.5 mm output can also be equipped with a microphone input. However, in this case it only carries the Anpec APA2068 2W stereo amplifier with 32-step volume control and more than a dozen passive support components. In the monitor settings there is no way to adjust the volume on the amplifier, which means that the firmware uses one of the fixed values.

Monitor repair | Board with navigation buttons

To simplify assembly, instead of individual plastic buttons, LG uses a single unit with S-shaped strips holding the buttons above the corresponding switches on the board. The slots on the board have different lengths, as do the ribs on the case. This solution will allow you to avoid fussing with them correct installation during reassembly.

Monitor repair | Power Switch Board

There's not much to see here: one switch and a block of two LEDs (yellow and blue). But there is room on the board for two more LED blocks. Apparently, LG decided that three LEDs were too expensive or they distracted the user. Or maybe at some point all three were used, but less bright.

Monitor repair | Protective cover

Under the steel cover are the display controller, power supply, and cold cathode fluorescent lamp (CCFL) inverters. The cover is attached to the LCD with two pieces of metallized adhesive tape.

The base clamp is screwed into the metal frame from below, removing part of the load from the plastic frame. There should be a shield above the CCFL wires on the left, but we forgot to put it in place before shooting.

Monitor repair | CCFL connection

This is what the CCFL power connectors look like with and without a shield. If you ever want to do any tests with these connectors, you should remember that CCFL lamps can have firing voltages in the region of 3kV. This is enough to burn test equipment or give you a nasty electric shock.

Monitor repair | Raise the lid

When you're ready to remove the electronics compartment from the back of the LCD, be careful with the LVDS cable connecting the panel to the display controller. The wires are thin, and the connector with miniature clips is quite flimsy.

And when we say miniature...

The connector is secured using two tiny hooks, about half a millimeter in size, that fold when the levers are pressed. It is unlikely that they will survive a sharp yanking from the nest. Wires of this diameter will also not tolerate rough handling.

Monitor repair | With electronics removed

This is what the display panel looks like without the electronics compartment. On the left are the CCFL power cables dangling. A small circuit board is hidden behind a perforated shield closer to the top edge. Almost the entire back surface of the LCD is covered thin sheet stainless steel, protecting the electronics and CCFL from each other. It may (or may not) serve as a reflector-diffuser for illumination, but while the lamps are alive, we will not find out.

This board has two functions. On the left we have a TI TPS65165 regulator that provides three different voltages to operate the panel driver. On the right, hidden under a thick thermal plate, is a sort of low-voltage differential signal (LVDS) repeater. Almost all unused space on the board has pinholes to dissipate heat and noise.

Below you can see a flat flexible cable going to the panel controller under the steel sheet. The cable is covered with reinforcing tape to protect it from damage.

Monitor repair | Inside the compartment

After removing the electronics box from the panel, you can turn it over. On the left we see the CCFL inverter, in the center is the power supply, and on the right is the display controller. There are shielding strips on the top and bottom edges of the compartment. There is little unused space here.

Monitor repair | Inverter board

The six CCFL LCD backlights are powered by three transformers with two secondary windings each. All three operate in parallel through a whole bridge of Anpec APM4008 N-transistors controlled by an MPS MP1038 CCFL controller. Since half of the board is under high voltage, on both sides it is covered with a glued plastic shield, eliminating the possibility short circuit on metal case. Three Samyoung NXH 35V 220µF curved capacitors look great even after six years of frequent use.

At this stage, no problems have been identified. All items are like new. Let's move on.

It looks like LG used an off-the-shelf CCFL inverter from Frontek Co. Information. Their products are quite rare and the website listed on the PCB seems to have fallen into oblivion. The code just below the transformer says the board was manufactured in week 13 of 2008, making it seven years old.

Monitor repair | Display control board

On the left you can see the HDMI, DVI and VGA inputs. In front of the display controller chip there is a signal switcher for DVI and HDMI. The small IC surrounded by capacitors is the DAC that serves the audio jack. There's nothing notable on the right third of the board other than two RAM chips and an LVDS connector.

We didn't immediately understand why the speaker was needed closer to the bottom left corner. But then we remembered that once upon a time we turned off the sounds of the interface (as well as turning on the monitor).

Monitor repair | Reverse side of the board

Before moving on to a detailed analysis of the board, let's take a quick look at its reverse side. As with many surface mount boards, the bulk of the components we're interested in are on top, while the underside contains various smaller components and wiring. In our case, mostly small capacitors are placed here. Light brown flux residue is visible throughout the board.

If you haven't already guessed, the areas with the solder strips are the heat spreaders of the two linear voltage regulators and the display controller.

Monitor repair | Connection with the past

The VGA connector is gradually going out of use. In the photo we can see neat soldering of ordered resistive capacitance (RC) filters on the left and resistor capacitance diode (RCD) input protection on the right.

Monitor repair | DVI input

DVI input protection is similar to that of VGA, even though it is entirely digital. The DDI chip and its own protection circuit are visible at the top. Below, starting on the right side, there are decoupling capacitors for input protection, clamping diodes at the input, and termination resistors with additional decoupling capacitors between the signal pairs. The lower left corner is occupied by a DVI/HDMI switch TI TMDS351 for three inputs, but only two are implemented on this board.

Monitor repair | HDMI input

Wiring elements near the HDMI interface looks much simpler. We couldn't find information on the chip labeled D1380747, but judging by the fact that all four TMDS signal pairs go straight through it, we can bet it's just an integrated eight-channel diode bridge. A third of the DDI EEPROM elements are located towards the bottom left corner, and their supporting components are not as densely placed on the board as the other two connectors.

Monitor repair | Let there be sound!

The rear 3.5mm audio jack must be connected to something. In our case, this is a Cirrus Logic CS4352 24-bit 192ksps DAC with a THD+N of 96 dB, which provides the theoretical maximum for CD audio. We haven't encountered him before. The layout is quite dense, but neat. Therefore, you can expect a fairly clean sound.

We checked the sound quality on headphones. Although there was no obvious noise or distortion at low volume levels, at levels as low as 20% of the volume in Windows, obvious disturbances began to appear.

Monitor repair | Controller

LG used an STMicro gm5868 display controller with external RAM chips to support frame rate conversion. Although the ST specification requires 1 MB of 75 MHz RAM, LG uses ESMT M12L16161A-5T 200 MHz chips, likely due to the fact that slow, low-density SDR memory is already practically extinct.

The little chip at the bottom is a 4Mbit Macronix MX25L4005 NAND device for storing UI bitmaps. And at the very top there is an EEPROM STMicro 24C16WP I2C 16 Kbit chip, which is used to store user settings.

Monitor repair | And now the main course

This article is called “disassembling and repairing the monitor,” but there has not been a word about repairs yet. It's time to fix this by moving on to disassembling the power module.

Since the PCB is single-sided, all surface components are on the bottom, including the two integrated circuits. The top IC is a PWM regulator for the 12V and 24V outputs, while the smaller chip in the lower right corner performs active power factor correction.

Monitor repair | But this is convenient

All main components and jumpers on top side for better identification, ease of signal tracking and troubleshooting are drawn on the bottom side. In some places there are drops of solder that accidentally fell on the board from the solder mask. Otherwise, the soldering quality is at a high level.

Monitor repair | Scarface

There is practically no marking on the APFC chip. It looks like little flakes have broken off from it. This happens after dipping into molten solder.

We looked for SOIC-8 APFC controllers with "280" in the model number, and the most likely candidate was the TI UCC28051D.

Monitor repair | Top of the board

If you look at the board from both sides, the basic wiring diagram is easy to read. Current enters the IEC plug on the left, goes to the input filter, passes through the bridge rectifier on the top heatsink, begins to return through the PTC, is filtered through the inductor and film capacitors, passes through the APFC circuit in the lower left corner, and then rises along the insulation boundary to the two outputs regulator

Have you already seen the failed elements?

Monitor repair | Characteristics

If you want to use this display's power supply for something else, the input and output power specifications printed on the board will come in handy.

The numbers in the upper left corner indicate that this board was manufactured in week 13 of 2008, the same as the fluorescent lamp. The numbers next to the manufacturing date indicate that the PCB was manufactured by Shanghai Wanzheng Circuit Board Co. Ltd and passed the 94V-0 flammability test.

Monitor repair | 5V power rail

The lower right corner is almost entirely devoted to the 5 V power supply circuit. There are no discrete external transistors here. The chip under the thick U-shaped copper heatsink drives the 5V transformer directly. Judging by the information on the board, you can get a current of up to 3 A at the output.

We replaced two large capacitors during the first repair. They are mounted on the 5V rail, just like the smaller original capacitor on the left. The swollen little capacitor on the right is on the 12V output, and we didn't change it during the first repair because it looked fine at the time.

Monitor repair | About the radiator

If you want to see the chip hidden under the copper heatsink, you need to remove the solder and straighten the legs. Since we still planned to use the W2452V display in our work, we did not dare to take such a risk.

We looked at a bunch of DIP-7 standby PWM regulators from various manufacturers to identify this chip, and the closest was the Sanken STR-A60xxH.

Monitor repair | Buses 12 V and 24 V

During the first repair, we were unable to promptly select appropriate replacement parts. The two large capacitors in the top right corner provide the 24V voltage required by the CCFL inverter. On the swollen capacitor on the left there was a huge mountain of dried electrolyte. But before filming, we accidentally knocked her down. The smaller capacitor underneath is for the 12V rail and doesn't look good either.

The two output rails are controlled by the ST L6599D controller using two MOSFETs under the heatsink.

Monitor repair | Let's take a closer look

This photo clearly shows the failed capacitor. After opening the monitor, we saw on its top an almost perfect cone of black dried electrolyte about 10 mm high. It's a pity that we accidentally shot it down before we had time to take a photo.

Some readers who have encountered a similar situation will probably recognize these capacitors. They belong to the infamous Samwha WB series, which was allegedly discontinued back in 1999, but they are even found in products from 2007-2008. And, oddly enough, you can easily buy them on the market in Shenzhen even today.

Monitor repair | The Last Centurion

The third and only clean looking original capacitor on the 5V rail (bottom left) is connected downstream to larger capacitors and an inductor that isolate it from most switching noise. This case illustrates well that even “bad capacitors” can last quite a long time if they are not exposed to strong current changes.

It is curious that according to the scheme, instead of this capacitor, another, more capacious one should have been used.

Monitor repair | Replacement capacitors

When replacing capacitors, people often forget to look at the ripple current characteristics. By studying the Samwha WB specifications, we were able to find out that 35V 1000mF capacitors are designed for a current of 2.7 A, 25 V 680mF capacitors have a more modest rating of 1.8 A, and 10 V capacitors can withstand only 1 A. We will install Epcos B41888 35 capacitors B 1000mF rated at 2.4 A, Panasonic FM 16V 2700mF rated at 3.6 A and FM 16V 1200mF rated at 2.5 A.

The stated characteristics of Epcos capacitors are slightly lower and may lead to their failure after a few years, on the other hand, high quality promotes slower aging.

Monitor repair | Replacement

Brand new capacitors look much better than old and swollen ones. Even the board itself has improved. Or do we just think so?

Monitor repair | Testing equipment

Before the monitor could be turned on and tested, it had to be almost completely assembled. Since the panel covers the board, we had to solder the wires and bring the busbars out. This is important because long wires add unnecessary noise, making switching processes appear much worse on the oscilloscope screen than they really are. In other words, ignore high-frequency noises and bursts.

Monitor repair | Let's look at the results

After scaling the oscilloscope screenshots, the grid became almost invisible. This happened because we placed two images with different original sizes in one picture.

Going from 680mF to 1200mF on the last 5V capacitor had no significant effect. The ripples looked a little better, while the blurrier lines were caused by a little more ringing. The lower ESR (effective series resistance) of the new capacitor provides less attenuation.

Monitor repair | Something more hopeful

We see a similar picture on the 12 V bus. We replaced the capacitor closest to the rectifiers with a model with a capacity of 2700mF, and the second one with a capacity of 1200mF, almost tripling the electrical capacitance of the bus. At best, the ripple was reduced by half, but with a decrease in ESR, the “ringing” increased noticeably.

It sounds unexpected, but two leaky, swollen Samwhas capacitors on the 12V rail performed their task just as well as our new super-capacitive capacitors.

Monitor repair | Better now

The readings on the 24 V bus look much better. Ripple dropped from 600-1000mVPP to a stable 200 mVPP, even without a large increase in capacitance (and despite the 100 kHz impedance of 27 mOhm for Epcos versus 18 mOhm for Samwha).

Out of curiosity, we tried to measure the parameters of the old 35V capacitors, but due to excessive leakage current, we were unable to collect data. It looks like they've done their job a long time ago.

Monitor repair | Standby power

Our multimeter and homemade current sensor showed that the monitor in standby mode draws 43 mA at a line voltage of 117.6 V. Total power is 5.5 VA. The part of the current waveform in which the phase lead is almost 90° indicates the input power EMI filter capacitors, while small ripples of up to 150 mA appear when the input capacitor saturates at peaks AC voltage. This pulsation is enough to reduce the advance to 61° and reduce the power factor to 0.49. Jumps above the measuring scale (up to 300 mA) are short pulses occurring in the APFC.

Subtract distortion (anything not 60Hz, including noise) and reactive power, and we get a net standby power of 1.7W.

Monitor repair | Turn on

Once the display is turned on, the APFC is activated and the current phase is almost identical to the voltage phase whenever the input line voltage exceeds 50 V. The input current of 504 mA with a 7° lead at a voltage of 117.1 V gives a total power of 59 VA, and the power factor is obtained 0.99 is an almost perfect result.

By removing minor distortion and reactive power, we got 57 W of usable power. The measurements were taken with the “No Signal” message on the monitor at 40% brightness. I wonder what the difference is between all these values before and after the repair? It's a pity that we didn't think to carry out similar measurements before replacing the capacitors.

Monitor repair | Let's sum it up

Replacing capacitors is one of the simplest and most accessible types of electronics repair, next in complexity to replacing fuses in a known working circuit (at least when the fuse is not internal and not soldered to the printed circuit board).

We are more concerned about the fact that many electronics manufacturers use capacitors that are barely able to survive the warranty period, instead of installing more reliable and comparable in price that can last up to ten years. Because of people like this" technical solutions“I would like the government to legislatively increase the minimum warranty period to at least three years. In this way, we can reduce the amount of “electronic” waste generated by low-quality products, and also not once again jeopardize the family budget.

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