lcd panel failure symptoms free sample

Liquid crystal displays (LCDs) are the most widely used display technology. Their applications cover TV, mobile phone, appliances, automotive, smart home, industrial meters, consumer electronics, POS, marine, aerospace, military etc. LCD screen display problem can occur for several reasons.

Effect of environmental conditions on the LCD assembly. Environmental conditions include both the effects of temperature and humidity, and cyclic loading.

Effect of manufacturing process. With the development of LCD for more than 40 years and the modern manufacturing equipment, this kind if defects are getting rear.

Common failures seen in LCDs are a decrease in screen contrast, non-functioning pixels or the whole display, and broken glass. Different kinds of LCD display problem need to have different kinds of fix methods or make the decision not worthwhile to repair.

Broken glassIf you accidently drop the LCD and you find it broken on the surface but the display still works. You might just break the touch panel; you can find a repair house or find a youtube video to replace the touch panel. If you find the display not showing, especially you find the fluid leaking out. You need to reply the whole display modules.

Dim LCD displayLCD can’t emit light itself. It uses backlight. Normally, the backlight is not fully driven, you can increase the LED backlight to make a dim LCD display brighter. But if you LCD display has been used for a long time, it is possible that the LED backlight has to be the end of life (not brightness enough) if you turn on 100% backlight brightness. In that case to fix LCD screen, you have to find a way to change the backlight. For some display, it is an easy job but it can be difficult for other displays depending on the manufacturing process.

Image sticking (Ghosting)Sometimes, you will find the previous image still appearing at the background even if you change to another image. It is also called burn in. This kind of failure doesn’t need to repair by professionals. You can simply shut off the display overnight, this kind of problem will go away. Please do remember that displaying a static image for a long time should be avoided.

With the modern manufacturing process and design, this kind of failure rarely happens. Normally, it is caused by no power. Please check if the battery dead or adapter (power supply) failure or even check if you have plug in firmly or with the wrong power supply. 99% the display will be back on.

LCD has white screen – If a LCD has a white screen which means the backlight is good. Simply check your signal input sources which are the most causes. It can also be caused by the display totally damaged by ESD or excess heat, shock which make the LCD controller broken or the connection failure which has to be repaired by professionals.

Blur ImagesAs the LCD images are made of RGB pixels, the screen shouldn’t be blur like old CRT displays. If you do see blur images, they might be caused by two reasons. 1) LCD has certain response time, if you are playing games or watch fast action movies, some old LCD displays can have image delays. 2) The surface of the LCD is made of a layer of plastic film with maximum hardness of 3H. If you clean the surface often or use the wrong detergent or solvent which cause the surface damage. To fix damage on LED screen it’s need to be changed with professionals.

If you have any questions about Orient Display displays and touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

1Case 6-Abnormal Display. Bad components in power section of t-con.Case 7-Noise. Solder defect or shorted components on t-con.Case 8-Abnormal Display. Bad components in power section of t-con.Case 9-Noise. Solder defect or shorted components on t-con.Case 10-Abnormal Display. Bad components in power section of t-con.Case 11-Abnormal Display. Bad components in power section of t-con.Case 12-Noise. Bad solder connections, shorted or open components on t-con.Case 13-Noise. Bad solder connections, shorted or open components on t-con.Case 14-No display and back lights are lit. T-con Fuse Open or Bad components in power section of t-con. No voltage to t-con from main board or power supply(main board or power supply failure).Case 15-No back light. Inverter failure or power supply failure.Case 16-Dim back light. Inverter failure.Case 17-Dim back light. Inverter failure.Case 18-Dim back light. Inverter failure.

2Case 19-Uneven display. cell defect.Case 20-Uneven display. cell defect.Case 21-Damage from applied pressure to panel. Bad panelCase 22-Crosstalk. cell defect.Case 23-Crosstalk. cell defect.Case 24-Panel cracked.Case 25-Vertical block. Failed driver IC, TCP/COF failed ACF bonding to panel bad connectionfrom driver IC to TCP/COF.Case 26-Vertical line. Failed driver IC, TCP/COF failed ACF bonding to panel, bad connectionfrom driver IC to TCP/COF.Case 27-Vertical block. Failed driver IC, TCP/COF failed ACF bonding to panel, bad connectionfrom driver IC to TCP/COF.Case 28-Vertical block. Failed driver IC, TCP/COF failed ACF bonding to panel, bad connectionfrom driver IC to TCP/COF.Case 29-Horizontal block. Failed driver IC, TCP/COF failed ACF bonding to panel, bad connectionfrom driver IC to TCP/COF.Case 30-Horizontal block. Failed driver IC, TCP/COF failed ACF bonding to panel, bad connectionfrom driver IC to TCP/COF.Case 31-Horizontal line. Driver IC abnormal output. Failed driver IC, TCP/COF failed ACF bonding topanel, bad connection from driver IC to TCP/COF.

3Case 32-Horizontal block. Failed driver IC, TCP/COF failed ACF bonding to panel bad connectionfrom driver IC to TCP/COF.Case 33-Horizontal block. Failed driver IC, TCP/COF failed ACF bonding to panel bad connectionfrom driver IC to TCP/COF.

COF= Chip on film/flexTCP= Tape carrier packageIC= Integrated circuitT-con= Timing controller(board)LCD= Liquid crystal displayACF= Anisotropic conductive film

In a situation where it seems that the screen is on but displays no image, the failure could be the power supply, the motherboard or the inverter (module that supplies current to the backlight).

Contact us to receive a diagnosis and repair. Our laboratory has advanced and innovative equipment to diagnose and repair any issue on PC LCD monitors. Our technicians provide professional and quick high-quality service. Many satisfied customers attested to that by leaving testimonials.

Issues with non-conforming performance, where the product no longer meets the performance specification, may be tied to a lack of quality of the components, LCD manufacturing, or in some rarer circumstance a change on the end-product that affected the LCD display.

Additionally there can be mechanical non-conformities, where there are aspects exceeding the defined tolerance as described in the specification. And in some instances, there may be variations not designated in the specification, but quite different from the original qualification units. These non-conformances are capable of affecting the fit, form, or function of the LCD display when assembled.

If your supplier has excessive component variability or possible process variability, there is the potential for a number of LCD display performance-related issues. These issues can be one-off or related to a larger batch of products manufactured together. Good serialization and traceability will help in isolating these occurrences and get to the root cause quickly.

While out-of-the-box nonconformance is typically the responsibility of the supplier, but it becomes a little more ambiguous when the non-conformance is not covered specifically by the governing specification. In this case, common sense and reasonable expectations of variation, the concept of the TEAM is considered. But at the end of the day, the LCD displays need to work in the finished product, and both parties should take the responsibility together to help get to the most efficient solution.

On the other hand, you need to be aware that performance degradation is sometimes caused by a change in another component upstream of the LCD display. Sometimes, a non-display component that is malfunctioning or is incompatible and interfaces with the display may cause the display to exhibit irregular behavior or render it inoperable altogether.

To verify this, swap displays to a fully functioning assembly and see whether the problem follows the display. If the issue does not reappear, the cause is likely a non-LCD display component.

Unfortunately, it is common for some failures to make it through final testing. After the vibration and thermal effects from the shipping process, these defects can be exposed and result in an out of box failure at the assembly line.

This could be a manufacturing issue during the LCD display production or a quality issue with an upstream component that exposed a failure mode. In this case, fault may lie with the design itself, which indicates the need for a more robust design. Alternatively, a burn-in test process may be needed to expose potential defects prior to final inspection.

The final assembly process could also be a problem area. If the process is complicated, difficult to maneuver, or there are new operators involved there is a much higher probability of damage while assembling the LCD display into the end-product.

Performing a failure analysis is next. Then, linking that analysis to the customer’s field environment. You’ll need to determine (1) whether the failure is caused by the environment and (2) whether a product improvement can better support the application, or whether there’s a way to limit the environmental extremes.

There is also the potential for misusing the product. A good example of this is using the product in an unintended environment such as extreme moisture. Impact is another unmistakable failure mode as it can manifest itself as a broken touch panel or cracked LCD glass.

Ever had your TV showing nothing but a black screen even if the audio was working? Unfortunately, that’s a common issue with low/middle-end LCD/LED TVs these days… Even more frustrating, this issue often comes from a rather tiny and cheap component that can be easily replaced. Most common issues are:

The first step into repair is to find the root cause of the issue. As backlight failure is a very common issue, this is the first thing to test. To do so, the easiest way is to power on your screen, put a flashlight very close to it and check if you can see the image through. The image would be very dark, like turning the brightness of the screen very very low.

That implies disassembling the TV to access the backlight which is between the LCD screen in the front and the boards in the rear. In my case, with a Samsung F5000, I had to process as follows:

First we have to remove the back housing to reveal the boards (from left to right: main board, T-CON, power supply) and disconnect the LCD panel from the T-CON board.

Note: Older TVs have neon tubes for backlight, which is thicker and less exposed to this kind of failure. LED backlight is the most common thing these days, but do not mistake an LED TV with an OLED TV. The first one is a classic LCD panel with a LED backlight, whereas the second is an OLED panel that doesn’t need any backlight as it is integrated in each pixels (making the spare parts much more expensive by the way).

There might be a lot of other root causes for similar symptoms, a black screen often looks like something very serious and therefore expensive to repair, but this case is the perfect example that taking some time to look for the root cause can sometime lead to a good surprise: here a 1$ fix!

Unfortunately, most of that stuff requires either a certified repair or a complete replacement to fix. Unless you’re especially handy with electronics and you just happen to have access to cheap replacement parts, it’s usually better to either return a monitor to the manufacturer (if it’s under warranty) or simply buy a new one. Even so, here are the most common ailments for modern LCD monitors, and what can be done to fix them…or not.

An incorrect refresh rate setting can also cause flickering. The refresh rate is the number of times the computer sends an image to the monitor per second, expressed in hertz. Most LCD monitors use either 59 or 60 hertz, though 75Hz, 120Hz, and 144Hz are also found on premium monitors. Go into your operating system’s display settings (right-click desktop and head to Display settings > Display adapter properties > Monitor in Windows 10) to make sure the right hertz setting is applied—you may need to update your video drivers as well.

Unfortunately, most other flickering symptoms are caused by a power deficiency somewhere in the monitor itself. It’s possible you could be drawing too much power from one of your home’s electrical circuits or overloading your surge protector—just move the power adapter to another plug to test this. But it’s more likely that there’s a loose or malfunctioning component in the screen assembly itself. If that’s the case, repair or replacement are the answers.

Black or single-colored lines on LCD screens are caused by a lot of different issues, but if the standard fixes outlined in the flickering section above don’t fix them (check your video and power cables for problems, install new drivers), it’s probably a physical defect in the screen itself. Try your monitor on another computer or laptop to see if the problem persists; if it does, you’re probably looking at a replacement, since the error is almost certainly in the LCD panel (the most expensive component of the monitor).

A “dead” pixel is a single dot on your LCD screen that doesn’t illuminate, showing up as one or more black squares. “Stuck” pixels are similar, but instead of showing black they’re stuck on a single color that doesn’t match the computer screen’s image, typically either red, green, or blue.

There isn’t much you can do for a dead pixel—it’s a physical malfunction of the screen panel. Luckily one or two dead pixels usually doesn’t mean you have to throw the whole monitor away; it’s certainly possible to work around it or ignore it. You can also look into a warranty replacement, though many monitor manufacturers won’t replace a screen until multiple pixels have gone out.

A stuck pixel may be a different matter. Depending on exactly how the problem is manifesting, it might be possible to get the pixel back into working order. There are various techniques for this, ranging from physically “massaging” the screen panel itself to running programs that rapidly cycle a portion of the screen through the color spectrum. You can try out some of these solutions as outlined in our guide to stuck pixels, but be warned, in my personal experience, it’s exceedingly rare to find a lasting solution to a stuck pixel.

If your monitor has a visible crack, a large discolored area, or a black/multicolored spot that doesn’t align with the pixel grid, it’s been subjected to physical trauma and the LCD panel is damaged. There’s nothing you can do here: even if your monitor is within its warranty period, it almost certainly won’t cover physical damage. You could try to replace the LCD panel itself, but since the replacement part will be almost as expensive as a new monitor anyway, you might as well start shopping.

Most of the above problems can happen to the LCD screens used in laptop PCs and tablets, too…but because of the compact build, they’re much harder to repair. That being said, the extra expense of a laptop versus a monitor might make it a much better candidate for a repair rather than a replacement. At the very least (assuming you’re out of the warranty period), it’s probably worth a diagnosis and quote at a repair shop, if you’re not comfortable replacing the screen assembly yourself.

Accidental Damage is any damage due to an unintentional act that is not the direct result of a manufacturing defect or failure. Accidental damage is not covered under the standard warranty of the product. Such damage is often the result of a drop or an impact on the LCD screen or any other part of the product which may render the device non-functional. Such types of damage are only covered under an Accidental Damage service offering which is an optional add-on to the basic warranty of the product. Accidental Damage must not be confused with an occasional dead or stuck pixel on the LCD panel. For more information about dead or stuck pixels, see the Dell Display Pixel Guidelines.

The LCD glass on the display is manufactured to rigorous specifications and standards and will not typically crack or break on its own under normal use. In general, cracked, or broken glass is considered accidental damage and is not covered under the standard warranty.

Spots typically occur due to an external force hitting the screen causing damage to the LCD panel"s backlight assembly. While the top layer did not crack or break, the underlying area was compressed and damaged causing this effect.

If your Dell laptop LCD panel has any accidental damage but the laptop is not covered by the Accidental Damage service offering, contact Dell Technical Support for repair options.

First, I would like to mention that both an LED TV and a LCD TV are actually LCD TVs except that first one has LED stripes and the latter one has CCFL Backlights- (Florescent Tubes).

This Blog is just Symptoms and Repair of different Models in Alphabetical order. These are real case history Symptoms and Repairs. For more information about different symptoms, sound, picture display, etc. and general repair tips, please visit my other blogs.

Repair- Suspect a stuck VOLUME down(-) button. A normal button will give you that tactile feel, compare it with the other buttons. If it feels similar to the other buttons then it could be the switch behind that button. The switch used in most front panel buttons are called ‘tact’ switch, obviously named because of that tactile feedback

This means that the Audio Processing Circuit on the Mainboard of your TV has failed. The mainboard is the board that houses all of the Audio Video jacks on the back of the TV and is accessible/replaceable by removing the of the set. You would need to replace this board to fix the problem, and it is a fairly common failure in this TV.

Repair–Suspect T-Con Board–Sometimes, just resitting, unplugging and re-plugging the flexible ribbon wire from the T-Con board to the LCD panel, will fix it-If not replace T-Con Board-

Symptom- the unit powers on with a steady red light on the front panel. However, I could not turn the unit on using either the remote or mechanical buttons. The red standby light never flashes and remains steady.

Emerson LF501EM5F TV Symptom- Bought it less than 2 years ago and now won’t turn on. The Led light is solid red once I plug it back in. I took the rear panel off and can hear a small humming sound in the marked location. Repair- Replace Main Board

Funai LC320SSX LCD TV- Symptom- ” It does not turn on at all. It use to turn and turn off then it just stop turning off” Repair- Bad capacitor on Power Board

Replace- Replaced the power board with a new one and replaced the main board as well and also replaced the t- con board–No ChangeRepair–1 burnt Led on LED Strip inside panel–

Hisense 50K23DG LED-LCD HDTV - 50K23DG Symptom- red light comes on, flashes 6 times Replace- Replaced the power board with a new one and replaced the main board as well and also replaced the t- con boardNo Change Repair1 burnt Led on LED Strip inside panel

Insignia NS-L42Q120-1-A LCD TVSymptom–The TV plays awesome beautiful pic, but powers down , I can turn it back on and it plays great! Then powers down– Repair–Firmware Update

Insignia NS 50D550NA15 TV Symptom- While watching the tv I could hear a sizzling sound a flickering light in the top right corner and then the picture faded to black . I have changed the power supply board and with the new board installed there is power and audio. I can see a picture doing a flashlight test but I do not see any backlights. Repair- Replaced Power Board, have sound no picture. Can see movement, with flashlight-Apparently, shorted Mosfet on Power Board, burnt LED strip inside panel.

Symptom–While I was fixing a ribbon cable on LCD screen TCON board popped. Replaced with new one but now my screen has sound but image is extremely bright. With image but no colors.

Repair–Replaced T-Con Board–No change. Found shorted VA1-(Variable Resistor) Since it is on the Control Board, which is Micro Soldered to the Panel and cannot be replaced, it`s considered as panel failure-

Activate the TV’s menu — let’s see if that flickers too. We want to see if the menu flickers, because it might be only the TV’s picture that flickers. If the menu flickers, then we know we’re dealing with the panel or the TCON. If only the picture flickers and the menu is steady, then we know we’re dealing with the Main board.

LG LED TV-50LN5310 Symptom–Turns on quick white flash (Backlights) then sound, no picture- Repair-Burnt Line inside panel on negative side–Re-soldered negative line on connector

Now, You only have 2 boards- Power Board and Main Board. What I need you to do, is disconnect the LVDS Cable, the cable that runs from, Main Board to T-Con at top of Panel–See picture below- Disconnect at red box, plug in TV. Does it come on–

Panasonic 42 THAS610D LED TV Symptom- backlights are looking fine, no picture- Repair- Checked SMD Fuse is good. Replaced T-Con, no difference When removing 1 FPC Cable(Cable at top of T-Con, we get 1/2 picture. Was considered panel Failure’

Philips LCD TVSmoke like shadow on one side of the screen It is most likely a LCD panel problem. It is costly and impractical to have it replaced. You can only discern the smoke like shadow on low light scenes

RCA 42″ Flat Screen TVSymptom–I have only half the screen is working . After it warms up the you can see the whole thing. Repair-This problem is either the T-Con Board or Panel Failure–

Symptom-When the TV is plugged in the Red Light is on-No Blinking-Then when I turn the set on with either the front panel Button or the remote control the light then goes off and nothing happens, No sound or picture

Repair-3 shorted LEDs inside panel–In stead of replacing strips, put a jumper resistor and soldered in–Use 5K Resistors is best–Remember his LEDs where in Sequence and not Parallel–

Samsung-LCD TV Multiple Color Vertical Lines- This type of TV problem, we must call out the OSD Menu to confirm–If the OSD Menu is showing normally on the screen, but the-background is full of color vertical lines then this symptom is caused by the Main Board or LVDS Cable–

The only thing you have to do is disconnect the cable between the power board and main board. Then, power on your TV. If you see the back light in the back of panel the problem is the main board if not, the power supply is the problem.

Sony LCD TVHas dim picture–1 of the CCFL(cold cathode fluorescent lamp/light) could have burnt or the circuit(inverter) that powers it might have failed. A technician will usually swap the connectors between the suspected dead lamp with the other good ones. The backlight consist of more than 2 CCFLs. When swapped and the dark area is at the same location then you have a bad lamp, otherwise suspect the inverter.

Sony 52″ LCD TVSymptom-Turns off by its self after a few minutes- Try to check first TIMER Settings on the TV set. Disable features such as auto-off and sleep timer. If everything seems to be ok, check air vent holes for possible obstruction and clean, maybe a sign of overheating.

Repair-Activate the TV’s menu — let’s see if that flickers too. We want to see if the menu flickers, because it might be only the TV’s picture that flickers. If the menu flickers, then we know we’re dealing with the panel or the T-CON Board. If only the picture flickers and the menu is steady, then we know we’re dealing with the Main board.

Symptom– Turns on, then says “Digital Television” then turns off.( Short flash of Light...and a short Display ) This type of failure is almost always caused by Inverter circuit failure, in the majority of LCD TV’s. Check the pico fuses or smd fuses and HV Transformers in the main inverter circuit, but with these models, I know that one of the HV Transformers, often develops a open a secondary winding. It is usually the HV Transformer, at location T1100

Symptom–Nothing happens if I press buttons from the remote control or even on the TV panel. If I unplug it for an extended period of time it seems to “boot up” right away and everything is fine.

In this quick guide we’ll cover what Dirty Screen Effect looks like, what’s happening on a technical level, and what, if anything, you can do to get rid of it. We’ll also touch on the notion of the so-called “panel lottery” and how that plays into how clean — or dirty — your new TV screen might look.

Dirty Screen Effect (DSE) is a term that’s used to describe an LCD panel that has inconsistent luminance performance across its surface area. It can appear as random splotches, uniform lines, wide bars, and, in some cases, vignetting (a slight darkening toward the corners). DSE once plagued plasma TV panels as well. But since those are no longer in production, we’ll keep this explainer focused on LCD-based TVs.

As a reminder, any TV that uses an LED backlight also uses an LCD panel, so TVs marketed as LED, QLED, and mini-LED are all susceptible. Due to what causes DSE on a technical level, some may argue it can only apply to LCD-based TVs. However, similar effects can be seen in OLED-based displays — thus the term is often applied — so we’ll include those types of TVs as well, but address them separately.

There are a number of factors stemming from the manufacturing of an LCD panel that can cause Dirty Screen Effect, from variance in backlight distribution to variance in TFT switching for sub-pixels, to variance in conductivity and/or capacitance of transparent electrodes. That’s super-nerdy, though, and the actual cause is less important than the common theme here: inconsistency.

In panel manufacturing, there are numerous variables that can be introduced that would cause an LCD panel to have groups of pixels that shine less bright than others. This variance is, unfortunately, part of the tech that makes our TVs. And the manner in which different manufacturers handle that variance is also … you guessed it: Varied.

Dirty Screen Effect also can be caused by damage to the panel in shipping or mishandling of the TV during the setup or installation process. Generally speaking, it’s recommended one avoids “pinching” or otherwise exerting pressure on the front of the TV screen.

From what I’ve seen, DSE — ranging from insignificant to severe — seems fairly common among newly manufactured LCD-based televisions, due primarily to the nature of LCD panel manufacturing. Very broadly, the less expensive a TV is, the more likely it is to exhibit some level of DSE. More expensive TVs are not immune to the issue, but some manufacturers have tighter quality assurance tolerances for their high-end products so — again, very broadly speaking — DSE tends to be less prevalent among those models.

DSE as a symptom of age is virtually impossible to track, however — again, anecdotally — I have witnessed DSE creep into a TV’s display panel slowly over time and worsen with age. I’ve seen it happen in TVs I own, TVs friends and family have owned, and TVs installed in commercial environments such as hotels and bars.

Unfortunately, there’s no way to eliminate DSE. Some websites suggest loosening the screws on the back of a TV to lessen the strain on the panel. We do not recommend this tactic as it could stand to void an active warranty. Also, it’s not very likely to work.

Most TVs offer a “game mode” which, due to its tendency to brighten everything on-screen, can help to obscure DSE. But this is really just a Band-Aid measure. The DSE is still there, but it may be less obvious. Another somewhat helpful tip to reduce the appearance of DSE in LCD panels is to view the TV from as direct an angle as possible. As you move off-axis (view a TV from an angle) DSE tends to become more obvious.

The so-called “panel lottery” refers to the game TV buyers unwittingly play when purchasing a TV. Sometimes you “win the panel lottery,” which is a way of saying that the TV you got was in especially pristine shape and shows no signs of DSE. It’s also a term used to easily express that there’s such a variance in panel quality that it’s virtually impossible you’ll win a perfect panel. In other words, it’s all up to chance.

LCD panels have steadily evolved over the last several years. New designs of the physical structure of the LCD crystals have greatly improved the contrast ratio and viewing angle. Quicker response times and increased refresh rates have helped to reduce the motion “smear” associated with LCD displays. Backlighting design has also aided in producing a picture with color temperatures to make the images as true as possible. With all these design improvements, one aspect of the LCD panel remains relatively the same: Processing of the video signal. A typical LCD panel and the associated video

processing circuits as found in the WAX3 chassis. The various formats and resolutions of video signals are processed on the BU1 board. All video signals exit the video processor in the native resolution of the LCD panel. In this design, the resolution is for a 1366 by 768 at 60HZ refresh rate panel. 48 horizontal lines are discarded to match up to the 720p resolution

of the ATSC specifications so the video will exit as 720p. The LCD panel used in this model processes 8-bit RGB video data. Before the video information can be sent to the TCON board it must be converted to a format that allows for practical and noise-free transmission. The large number of parallel lines to transmit the 8-bit RGB data would need to be sent on differential lines for noise reduction. This would require 48 lines just for the video. The TCON circuit also requires B+, ground connections, a communications bus, sync, and a clocking line transmitted differentially so we can see that up to 60 lines would be required for an 8-bit video signal and significantly more lines for a 10-bit processor. The practical way to transmit this information is to convert the parallel video data to a serial stream and this is accomplished by the Low-Voltage Differential Signaling (LVDS) transmitter.

The LVDS transmitter contains a circuit to serialize the parallel data. The parallel video information along with sync and clocking data are transmitted via twisted line pairs. Depending on the logic level, current is sent along one or the other of the twisted pair of wires. The receiving end of the wires is loaded with a resistor (usually around 100 to 120 ohms). The receiver detects the polarity of the voltage drop across the resistor to determine the logic level. The current level swings in the wire are about 3ma with a voltage differential of around 350mv. This allows for transmission of the video signal with minimal EMI. The LVDS receiver on the TCON board converts the serialized data back to parallel. This data is processed by the timing control IC to allocate the RGB data into serial streams for processing by the LCD panel. The TCON transmits the pixel control data to the panel via flat, flexible circuit board cables which can number 2 or 4 depending on the bit rate and refresh timing of the panel. A 1366 X 768 panel requires about 180 lines to transmit control information and B+ from the TCON. This number of control lines is not even close to the number of horizontal or vertical rows of pixels so the LCD panel must use this information to further expand the ability to turn on each individual crystal. The process will be explained in the gate and source driver paragraphs. All of this is accomplished by the TCON board. The term “TCON” is short for Timing Control. Other LCD panel manufacturers may have a different name for this particular circuit but the term used by Sony will always be TCON.

Referring to Figure 4-5, note the IC’s located along the side of the panel. These IC’s are mounted on a flexible cable(s) which are bonded to the LCD panel. Their function is to activate each row of pixels one at a time starting with the first line at the top. As each line is activated, the source drivers turn on the appropriate liquid crystals for the frame of video about to be displayed. This continues from top to bottom until the entire frame of video is displayed. The process is repeated for the next frame. This rate can vary from 60 times per second or be increased to 120 or 240 as found in the high-frame-rate panels.

These IC’s provide the control voltages to turn on each RGB segment of the vertical rows of pixels. In this example, the panel has a horizontal resolution of 1366 pixels. Each pixel is made up of a red, green and blue liquid crystal which means there are 4,098 columns to control. The source drive IC’s contain shift registers along with buffer switches. Shift registers are used to convert serial data to parallel. By using this method, the TCON is able to transmit control information to each of the source drivers using serial data lines. If the TCON is transmitting 8-bit data to the panel, each data line is capable of controlling 256 lines exiting the source drivers. Understanding how the gate and source drivers work together makes it easier to observe a problem on the screen and determine if the failure is panel or TCON related.

In order for this concept to move forward successfully, it is important that the service industry be able to properly identify the symptoms of TCON issues to avoid unnecessary service calls and repair costs. Accurate analysis of TCON failures will reduce costs significantly (both in parts costs and time) when warranty repairs are involved and will reduce the number of COD repairs that are lost. A good approach when determining a TCON failure is a good understanding of which symptoms ARE NOT caused by the TCON. Examples are as follows:

Video Process Failures: All video inputs received by the video process circuits are handled on a frame-by-frame basis. The video frames are converted and scaled to 8 or 10-bit RGB information. It is virtually impossible for the video process circuits to cause a problem on a specific area of the screen. Failures on this board usually appear as distortions, color level shifts, video level shifts, noise that involves the entire picture, or no picture at all. The TCON can generate symptoms that appear to be video process related but the video process circuits cannot produce the symptoms of a failed TCON circuit.

LVDS Cable Failures: Although problems with the LVDS cable or connectors can generate symptoms of TCON failures this usually tends to be intermittent and wiggling of the connectors will usually provoke a change in the symptom on the screen. LVDS cables and connectors have become rather robust over the past few years and most problems are caused by one who works with it damage them and this is generally quite obvious upon close examination.

LCD Panel Failures: Some LCD panel failures could possibly be mistaken for TCON issues. Other than damage to the LCD glass, most panel failures are isolated to a particular area of the screen. Since the TCON disperses the pixel data to groups of line and column drive IC’s situated on the outer edges of the panel, it is unlikely that more than one of these IC’s would fail at the same time. Multiple columns of stuck on or stuck off pixels are, therefore, more likely to be the fault of the TCON circuits. The same applies to a single row of lit or unlit pixels. The TCON simply cannot cut out a single line of information.

• Physical damage such as cracks in the panel, a single pixel or group of pixels that always on or off, or random sections of the panel which are completely dark.

• Source driver failure. This symptom appears as a single vertical band around 1 to 2 inches (depending on the panel size) and can be black, white, or any other color. It can also contain video information with distortion. A single vertical line that is dark or colored. This may be due to a tab bonding failure from the IC to the panel but either cause requires the replacement of the panel.

• Gate driver failure. These IC’s operate in a “bucket brigade” fashion. As mentioned earlier, the gates drivers scan each horizontal line starting at the top. If any one of the gate drivers fails, all of the subsequent drivers below it will fail to operate properly. This symptom is usually indicated by normal video on the upper portion of the screen followed by distorted video from the point of the failed IC and downward.

• Any horizontal lines. The gate drivers are activated by a single source of timing information so any single horizontal line or groups or random horizontal lines are caused by an output failure from a gate driver or a loss of the tab bond to the panel.

Failures in the timing control circuits of the TCON can produce symptoms of absolutely no video or generate lines and patterns that usually cover all or a substantial part of the screen. Determining if the TCON is the cause of a “no video” condition is a bit more difficult since there are no indications on the screen to analyze.

many of the Sony television models over the last few years will detect a TCON that has completely failed. The communications data between the video process circuits and the TCON will cease to communicate if the TCON fails completely. This will cause the television to shut down and display a diagnostics code indicating a failure of the TCON. Not all chassis designs have this feature and it is not found on older models.The typical scenario when this failure arises is for the technician to bring a video process board to the repair location. It is usually safe to assume that the problem lies on the TCON board if the replacement video board does not remedy the problem since it is highly unlikely that a replacement board with the same failure was received. One trick to check most TCONS for functionality is to loosen the LVDS connector at the TCON (as shown In Figure 4-3) while the unit is turned on. Handle the LVDS connector with care and be certain to fully release the lock tabs. Gently rock the cable in and out of the connector while observing the screen for any response. Depending on the chassis, the symptoms of the screen may be gentle white flashes, intermittent colored lines, or a screen full of random patterns. The idea at this point is to provoke some kind of response on the screen. TCON boards that have failed will not usually generate any type of response on the screen. Another helpful procedure is to rapidly heat and/or cool the TCON with hot air devices or circuit coolant and watch for patterns to appear on the screen.

Illustrates 2 examples of a loss of control data to the drive IC’s. In the first example, an entire group of column drivers has lost the data stream for red. The second example involves the complete loss of drive data for all RGB information to the right side of the screen. This is sometimes caused by the flat cable connecting the TCON to the LCD panel coming loose. The area of missing video can be dark or completely white depending on the panel design. Service Tip: Select an inactive input (or one that is known to be a 4:3 SD source) and toggle between the “normal” and “zoom” modes. If the lines follow the zoom changes, the problem is located on the video process board. If they stay in the same place, they are originating in the TCON Or LCD panel.

Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is switched ON. Vertical ridges etched on the surface are smooth.

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directlybacklight or reflector to produce images in color or monochrome.seven-segment displays, as in a digital clock, are all good examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.

LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, calculators, and mobile telephones, including smartphones. LCD screens have replaced heavy, bulky and less energy-efficient cathode-ray tube (CRT) displays in nearly all applications. The phosphors used in CRTs make them vulnerable to image burn-in when a static image is displayed on a screen for a long time, e.g., the table frame for an airline flight schedule on an indoor sign. LCDs do not have this weakness, but are still susceptible to image persistence.

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, often made of Indium-Tin oxide (ITO) and two polarizing filters (parallel and perpendicular polarizers), the axes of transmission of which are (in most of the cases) perpendicular to each other. Without the liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. Before an electric field is applied, the orientation of the liquid-crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic (TN) device, the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.

The chemical formula of the liquid crystals used in LCDs may vary. Formulas may be patented.Sharp Corporation. The patent that covered that specific mixture expired.

Most color LCD systems use the same technique, with color filters used to generate red, green, and blue subpixels. The LCD color filters are made with a photolithography process on large glass sheets that are later glued with other glass sheets containing a TFT array, spacers and liquid crystal, creating several color LCDs that are then cut from one another and laminated with polarizer sheets. Red, green, blue and black photoresists (resists) are used. All resists contain a finely ground powdered pigment, with particles being just 40 nanometers across. The black resist is the first to be applied; this will create a black grid (known in the industry as a black matrix) that will separate red, green and blue subpixels from one another, increasing contrast ratios and preventing light from leaking from one subpixel onto other surrounding subpixels.Super-twisted nematic LCD, where the variable twist between tighter-spaced plates causes a varying double refraction birefringence, thus changing the hue.

LCD in a Texas Instruments calculator with top polarizer removed from device and placed on top, such that the top and bottom polarizers are perpendicular. As a result, the colors are inverted.

The optical effect of a TN device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, TN displays with low information content and no backlighting are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). As most of 2010-era LCDs are used in television sets, monitors and smartphones, they have high-resolution matrix arrays of pixels to display arbitrary images using backlighting with a dark background. When no image is displayed, different arrangements are used. For this purpose, TN LCDs are operated between parallel polarizers, whereas IPS LCDs feature crossed polarizers. In many applications IPS LCDs have replaced TN LCDs, particularly in smartphones. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

Displays for a small number of individual digits or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment.alphanumeric or variable graphics displays are usually implemented with pixels arranged as a matrix consisting of electrically connected rows on one side of the LC layer and columns on the other side, which makes it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequentially addressing one side of the matrix, for example by selecting the rows one-by-one and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes see passive-matrix and active-matrix addressed LCDs.

LCDs are manufactured in cleanrooms borrowing techniques from semiconductor manufacturing and using large sheets of glass whose size has increased over time. Several displays are manufactured at the same time, and then cut from the sheet of glass, also known as the mother glass or LCD glass substrate. The increase in size allows more displays or larger displays to be made, just like with increasing wafer sizes in semiconductor manufacturing. The glass sizes are as follows:

Until Gen 8, manufacturers would not agree on a single mother glass size and as a result, different manufacturers would use slightly different glass sizes for the same generation. Some manufacturers have adopted Gen 8.6 mother glass sheets which are only slightly larger than Gen 8.5, allowing for more 50 and 58 inch LCDs to be made per mother glass, specially 58 inch LCDs, in which case 6 can be produced on a Gen 8.6 mother glass vs only 3 on a Gen 8.5 mother glass, significantly reducing waste.AGC Inc., Corning Inc., and Nippon Electric Glass.

In 1922, Georges Friedel described the structure and properties of liquid crystals and classified them in three types (nematics, smectics and cholesterics). In 1927, Vsevolod Frederiks devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology. In 1936, the Marconi Wireless Telegraph company patented the first practical application of the technology, "The Liquid Crystal Light Valve". In 1962, the first major English language publication Molecular Structure and Properties of Liquid Crystals was published by Dr. George W. Gray.RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what are now called "Williams domains" inside the liquid crystal.

In the late 1960s, pioneering work on liquid crystals was undertaken by the UK"s Royal Radar Establishment at Malvern, England. The team at RRE supported ongoing work by George William Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals, which had correct stability and temperature properties for application in LCDs.

The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968.dynamic scattering mode (DSM) LCD that used standard discrete MOSFETs.

On December 4, 1970, the twisted nematic field effect (TN) in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors.Brown, Boveri & Cie, its joint venture partner at that time, which produced TN displays for wristwatches and other applications during the 1970s for the international markets including the Japanese electronics industry, which soon produced the first digital quartz wristwatches with TN-LCDs and numerous other products. James Fergason, while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute, filed an identical patent in the United States on April 22, 1971.ILIXCO (now LXD Incorporated), produced LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971, for an electronic wristwatch incorporating a TN-LCD.

In 1972, the concept of the active-matrix thin-film transistor (TFT) liquid-crystal display panel was prototyped in the United States by T. Peter Brody"s team at Westinghouse, in Pittsburgh, Pennsylvania.Westinghouse Research Laboratories demonstrated the first thin-film-transistor liquid-crystal display (TFT LCD).high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.active-matrix liquid-crystal display (AM LCD) in 1974, and then Brody coined the term "active matrix" in 1975.

In 1972 North American Rockwell Microelectronics Corp introduced the use of DSM LCDs for calculators for marketing by Lloyds Electronics Inc, though these required an internal light source for illumination.Sharp Corporation followed with DSM LCDs for pocket-sized calculators in 1973Seiko and its first 6-digit TN-LCD quartz wristwatch, and Casio"s "Casiotron". Color LCDs based on Guest-Host interaction were invented by a team at RCA in 1968.TFT LCDs similar to the prototypes developed by a Westinghouse team in 1972 were patented in 1976 by a team at Sharp consisting of Fumiaki Funada, Masataka Matsuura, and Tomio Wada,

In 1983, researchers at Brown, Boveri & Cie (BBC) Research Center, Switzerland, invented the passive matrix-addressed LCDs. H. Amstutz et al. were listed as inventors in the corresponding patent applications filed in Switzerland on July 7, 1983, and October 28, 1983. Patents were granted in Switzerland CH 665491, Europe EP 0131216,

The first color LCD televisions were developed as handheld televisions in Japan. In 1980, Hattori Seiko"s R&D group began development on color LCD pocket televisions.Seiko Epson released the first LCD television, the Epson TV Watch, a wristwatch equipped with a small active-matrix LCD television.dot matrix TN-LCD in 1983.Citizen Watch,TFT LCD.computer monitors and LCD televisions.3LCD projection technology in the 1980s, and licensed it for use in projectors in 1988.compact, full-color LCD projector.

In 1990, under different titles, inventors conceived electro optical effects as alternatives to twisted nematic field effect LCDs (TN- and STN- LCDs). One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates.Germany by Guenter Baur et al. and patented in various countries.Hitachi work out various practical details of the IPS technology to interconnect the thin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels.

Hitachi also improved the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS). NEC and Hitachi become early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens. In 1996, Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2006.South Korea and Taiwan,

In 2007 the image quality of LCD televisions surpassed the image quality of cathode-ray-tube-based (CRT) TVs.LCD TVs were projected to account 50% of the 200 million TVs to be shipped globally in 2006, according to Displaybank.Toshiba announced 2560 × 1600 pixels on a 6.1-inch (155 mm) LCD panel, suitable for use in a tablet computer,

In 2016, Panasonic developed IPS LCDs with a contrast ratio of 1,000,000:1, rivaling OLEDs. This technology was later put into mass production as dual layer, dual panel or LMCL (Light Modulating Cell Layer) LCDs. The technology uses 2 liquid crystal layers instead of one, and may be used along with a mini-LED backlight and quantum dot sheets.

Since LCDs produce no light of their own, they require external light to produce a visible image.backlight. Active-matrix LCDs are almost always backlit.Transflective LCDs combine the features of a backlit transmissive display and a reflective display.

CCFL: The LCD panel is lit either by two cold cathode fluorescent lamps placed at opposite edges of the display or an array of parallel CCFLs behind larger displays. A diffuser (made of PMMA acrylic plastic, also known as a wave or light guide/guiding plateinverter to convert whatever DC voltage the device uses (usually 5 or 12 V) to ≈1000 V needed to light a CCFL.

EL-WLED: The LCD panel is lit by a row of white LEDs placed at one or more edges of the screen. A light diffuser (light guide plate, LGP) is then used to spread the light evenly across the whole display, similarly to edge-lit CCFL LCD backlights. The diffuser is made out of either PMMA plastic or special glass, PMMA is used in most cases because it is rugged, while special glass is used when the thickness of the LCD is of primary concern, because it doesn"t expand as much when heated or exposed to moisture, which allows LCDs to be just 5mm thick. Quantum dots may be placed on top of the diffuser as a quantum dot enhancement film (QDEF, in which case they need a layer to be protected from heat and humidity) or on the color filter of the LCD, replacing the resists that are normally used.

WLED array: The LCD panel is lit by a full array of white LEDs placed behind a diffuser behind the panel. LCDs that use this implementation will usually have the ability to dim or completely turn off the LEDs in the dark areas of the image being displayed, effectively increasing the contrast ratio of the display. The precision with which this can be done will depend on the number of dimming zones of the display. The more dimming zones, the more precise the dimming, with less obvious blooming artifacts which are visible as dark grey patches surrounded by the unlit areas of the LCD. As of 2012, this design gets most of its use from upscale, larger-screen LCD televisions.

RGB-LED array: Similar to the WLED array, except the panel is lit by a full array of RGB LEDs. While displays lit with white LEDs usually have a poorer color gamut than CCFL lit displays, panels lit with RGB LEDs have very wide color gamuts. This implementation is most popular on professional graphics editing LCDs. As of 2012, LCDs in this category usually cost more than $1000. As of 2016 the cost of this category has drastically reduced and such LCD televisions obtained same price levels as the former 28" (71 cm) CRT based categories.

Monochrome LEDs: such as red, green, yellow or blue LEDs are used in the small passive monochrome LCDs typically used in clocks, watches and small appliances.

Today, most LCD screens are being designed with an LED backlight instead of the traditional CCFL backlight, while that backlight is dynamically controlled with the video information (dynamic backlight control). The combination with the dynamic backlight control, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan, simultaneously increases the dynamic range of the display system (also marketed as HDR, high dynamic range television or FLAD, full-area local area dimming).

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure (prism sheet) to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman),

A pink elastomeric connector mating an LCD panel to circuit board traces, shown next to a centimeter-scale ruler. The conductive and insulating layers in the black stripe are very small.

A standard television receiver screen, a modern LCD panel, has over six million pixels, and they are all individually powered by a wire network embedded in the screen. The fine wires, or pathways, form a grid with vertical wires across the whole screen on one side of the screen and horizontal wires across the whole screen on the other side of the screen. To this grid each pixel has a positive connection on one side and a negative connection on the other side. So the total amount of wires needed for a 1080p display is 3 x 1920 going vertically and 1080 going horizontally for a total of 6840 wires horizontally and vertically. That"s three for red, green and blue and 1920 columns of pixels for each color for a total of 5760 wires going vertically and 1080 rows of wires going horizontally. For a panel that is 28.8 inches (73 centimeters) wide, that means a wire density of 200 wires per inch along the horizontal edge.

The LCD panel is powered by LCD drivers that are carefully matched up with the edge of the LCD panel at the factory level. The drivers may be installed using several methods, the most common of which are COG (Chip-On-Glass) and TAB (Tape-automated bonding) These same principles apply also for smartphone screens that are much smaller than TV screens.anisotropic conductive film or, for lower densities, elastomeric connectors.

Monochrome and later color passive-matrix LCDs were standard in most early laptops (although a few used plasma displaysGame Boyactive-matrix became standard on all laptops. The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an active-matrix display (though still monochrome). Passive-matrix LCDs are still used in the 2010s for applications less demanding than laptop computers and TVs, such as inexpensive calculators. In particular, these are used on portable devices where less information content needs to be displayed, lowest power consumption (no backlight) and low cost are desired or readability in direct sunlight is needed.

STN LCDs have to be continuously refreshed by alternating pulsed voltages of one polarity during one frame and pulses of opposite polarity during the next frame. Individual pixels are addressed by the corresponding row and column circuits. This type of display is called response times and poor contrast are typical of passive-matrix addressed LCDs with too many pixels and driven according to the "Alt & Pleshko" drive scheme. Welzen and de Vaan also invented a non RMS drive scheme enabling to drive STN displays with video rates and enabling to show smooth moving video images on an STN display.

Bistable LCDs do not require continuous refreshing. Rewriting is only required for picture information changes. In 1984 HA van Sprang and AJSM de Vaan invented an STN type display that could be operated in a bistable mode, enabling extremely high resolution images up to 4000 lines or more using only low voltages.

High-resolution color displays, such as modern LCD computer monitors and televisions, use an active-matrix structure. A matrix of thin-film transistors (TFTs) is added to the electrodes in contact with the LC layer. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is selected, all of the column lines are connected to a row of pixels and voltages corresponding to the picture information are driven onto all of the column lines. The row line is then deactivated and the next row line is selected. All of the row lines are selected in sequence during a refresh operation. Active-matrix addressed displays look brighter and sharper than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images. Sharp produces bistable reflective LCDs with a 1-bit SRAM cell per pixel that only requires small amounts of power to maintain an image.

Segment LCDs can also have color by using Field Sequential Color (FSC LCD). This kind of displays have a high speed passive segment LCD panel with an RGB backlight. The backlight quickly changes color, making it appear white to the naked eye. The LCD panel is synchronized with the backlight. For example, to make a segment appear red, the segment is only turned ON when the backlight is red, and to make a segment appear magenta, the segment is turned ON when the backlight is