Master Electronics Repair !

Welcome to Master Electronics Repair! website.Here you will find:Service Modes, Circuit Diagrams,Service manuals, Firmware Update procedure, Disassemble procedure, Universal remote control setup codes, Troubleshooting, Diagnosing, Measuring, and more.... of many of LCD/LED TV/Displays,others various electronic apparates,trough many technical notes and tips/tricks to help repairing/fixing Troubles/ faults,for electrical technicians.This site helps you to save the Earth from electronic waste!

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!

Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

How to use the site:

- If you landed here via any Search Engine, you will get what you searched for and you can search more using the search this blog feature provided by Google. You can visit more posts scrolling the left blog archive of all posts of the month/year,
or you can click on the main photo-page to start from the main page. Doing so it starts from the most recent post to the older post simple clicking on the Older Post button on the bottom of each page after reading , post after post.

You can even visit all posts, time to time, when reaching the bottom end of each page and click on the Older Post button.

- If you arrived here at the main page via bookmark you can visit all the site scrolling the left blog archive of all posts of the month/year pointing were you want , or more simple You can even visit all blog posts, from newer to older, clicking at the end of each bottom page on the Older Post button.
So you can see all the blog/site content surfing all pages in it.

- The search this blog feature provided by Google is a real search engine. If you're pointing particular things it will search IT for you; or you can place a brand name in the search query at your choice and visit all results page by page. It's useful since the content of the site is very large.

Note that if you don't find what you searched for, try it after a period of time; the site is a never ending job !

..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Monday 11 March 2019

LED BACK LIGHTING IN LCD TELEVISION - TOSHIBA TV LED LIGHTING

LED BACK LIGHTING IN LCD LED TELEVISION - TOSHIBA TV LED LIGHTING

LED BACK LIGHTING IN LCD TELEVISION

TOSHIBA LED BACK LIGHTING FOR LCD TELEVISIONS

The intent of this paper is to familiarize Electronic Servicers with what will be the central component in the new generation of flat screen televisions. With the ever growing popularity of LCD televisions, research and development has produced a method of back lighting an LCD panel that is superior to the Cold Cathode Fluorescent (CCFL) Backlighting, currently the most popular amongst television manufacturers. The new method employs a Light Emitting Diode Array, commonly referred to as “LED Array” or, an in-line strip of individual LED’s, referred to as “Edge Lit”. This paper is a basic explanation of how LED backlighting works. There are many algorithms applied to the IC’s involved in the LED Dimming process. This paper does not intend to go into the engineering behind this very complicated process.

WHY LED

LED backlighting is an evolution of basic LCD technology. For a comprehensive understanding of basic LCD technology, it is recommended you review Toshiba White Paper, 2.0, “LCD Television Technology”.

Assuming basic LCD technology is understood, we will discuss the need for evolving to LED backlighting. There are inherent difficulties with the CCFL method of backlighting:

1. CCFL requires an inverter to supply 400-700 volts AC as an operating voltage for the lamps. This results in heavy power requirements.

2. True “Black” areas of the picture are not attainable because the CCFL lamps are always on. This allows for leakage of light through the liquid crystal materials even when the crystals are “turned off”. The contrast ratio (true white to true black) suffers greatly because of this.

3. Motion blur is difficult to minimize using the CCFL method of backlighting (constantly on backlighting) due to the relatively slow response time (transition time from off to on to off) of the TFT circuitry in the panel.

4. CCFL average life span is 20,000 hours.

Physical Comparison

Figure shows a graphic of a conventional LCD panel utilizing a standard CCFL backlight assembly. You will notice the inverter, lamps, and diffuser.

Figure showed is a drawing of two LED lighted panels; one Edge Lit, one LED array.

All three panels shown require lighting and a diffuser. At this stage, the main difference is the inverter (required by CCFL method). Of the two LED backlight designs, the LED array offers more precise brightness/contrast control and will therefore, be the method discussed in this paper.

An LED Array obviously requires a power source (Driver Board). An LED Array that is not intended for use as a brightness/contrast controller can be powered by a simple DC power source producing a constant current. This method will produce a pre-determined brightness level uniformly throughout the entire panel. The end result would be comparable to using a CCFL or Edge Lit Backlight. Therefore, another type power source must be used to achieve more precise control when using an LED Array. Figure 3 is a close-up of an LED array showing a driver and the driver PCB.

Pulse Width Modulation (PWM)

By changing the “On” time and “Amplitude” of a DC voltage, we can achieve control of the current flow through an LED Array at specific times. See Figure

In Figure we can see that the average current flow through the array in a given time period is 100ma. However, by using PWM, we are only driving the array for 1/5th the time with 5 times the current. If 100ma was the desired current for a normal brightness level, we could achieve normalcy on the LCD Panel in 1/5th the time. The human eye has a built-in retention for the highest brightness level applied. This retention gives the perception of a brightness level closer to the 500ma drive than the 100ma drive. Therefore, when a brightness level higher than what is considered normal (desired) is required by the signal, PWM can provide that level (perceived by the human eye). In order to prevent noticeable changes in applied light (flicker), the pulse repetition rate must be higher than 100hz and less than 1khz. One of the side benefits of PWM is decreased power requirements due to the decreased duty cycle (up to 30% less power compared to CCFL).

Applying the Theory

Now, let’s apply the PWM theory to an LCD Panel using an LED Array for back lighting. Refer to following Figure.

If the LED array is divided into sections (grids) and each section lights a small portion of the entire LCD panel (also sectioned into grids), the brightness level in one particular section can easily be controlled using PWM in conjunction with data from the T-Con and Video Processing circuitry. For example, if the processed video is calling for a bright picture in the upper right portion of the LCD panel, the backlight section(s) in that area will be told to provide the required brightness level. This synchronization between the Video Processor, T-Con, and LED circuitry will occur across the entire LCD panel thus, improving brightness (where called for) across the display.

About Dark Scenes

The refresh rate of the panel is either 60, 120, or 240 times per second. Those are the rates that scene changes may occur. When the processed video requires pixels to become dark (black), during a refresh cycle, the Thin Film Transistors (TFT”s) that drive the LCD’s for those pixels are told to shut-off. Because of the charging capacitor in the TFT circuitry, there is a slight delay in shutting down the LCD. To compensate for that delay, the LED array section in that particular grid will also be told to turn-off. The response time of the LED’s are instantaneous therefore, eliminates any chance of light being passed through the LCD Material of those pixels. This produces much darker areas of black, improving the Contrast Ratio. For a refresher, see Figure bellow (LCD Matrix with TFT’s and capacitors).

Having the ability to increase the brightness of the backlight during bright scenes and shut-off (or decrease) the backlight during dark (black) scenes can produce dynamic contrast ratios of up to 2,000,000 to 1. In comparing the life expectancy of LED to that of CCFL, the LED backlighting lasts up to 2 ½ times longer. The fact the response time is almost instantaneous in an LED, motion blur is reduced when the backlight is shut-off at the same time the TFT is commanded to shut-off. There can be no brightness lag if there is no backlight applied to illuminate the liquid crystal material.