REPAIRING AND NOT THROWING AWAY

REPAIRING AND NOT THROWING AWAY

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.

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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 !

Wednesday, 20 March 2019

LG 47LG90 LED LCD TV - BACK LIGHT - WORKING PRINCIPLE - TESTING BACK LIGHT BLOCKS - LOCAL DIMMING

LG 47LG90 LED LCD TV - BACK LIGHT - WORKING PRINCIPLE - TESTING BACK LIGHT BLOCKS - LOCAL DIMMING



INVERTERS [BACK-LIGHT LED DRIVE]
NEW: This set utilizes LEDs as backlights driven by the Inverters. These LEDs are manipulated in accordance to the necessary Light Source intensity according to the video content (Contrast Ratio) demands.  Control signals to the Inverters are sent out from the T-CON PWB.  B+ (24V) is sent from the Power Supply (SMPS).  There are 8 Vertical columns and 16 horizontal rows for a total of 128 individual LED Blocks. Each Block contains 12 LEDs (3 X 4).
THE BENEFITS OF LED BACK-LIGHTING
  • Much brighter & longer life time - LED100K hoursvs. CCFL 60K hours.
  • Expanded color gamut - 110% of ATSC gamut (vs. 90% for CCFL)
  • Eco friendly (No Hg “Mercury) & less power consumption.
  • Mega Contrast - (2,000,000:1dynamic Contrast Ratio.
LED BACK-LIGHTING
CCFL BACK-LIGHTING
LED BACK-LIGHT SECTION [FOUR BLOCKS]
BACK-LIGHT SECTION - SINGLE BLOCK
BACK-LIGHT INVERTER SECTIONS"M" & "S"
LED LAYOUT
The picture below shows a close up of one of the 1536 individual LEDs contained within the backlights. There are two sides each with 768 LEDs (64 blocks) in each side.  And individual block is manipulated by the T-CON board. These blocks are manipulated Global (All at once) and in accordance with the video intensity at the specific location of the block of LEDs for that video content (Local). In other words, if the video is dark in the area of the screen that is being illuminated by a block of LEDs, they will be dimmed.  Not counting “Black” there are 3 levels of intensity of the LEDs.  The Overall intensity of the backlights is manipulated by the “Global” Dimming signal from the BCM chip called Digital-Dimming.
  • A minimum of 30V required to light all 12 LEDs in a block Bottom 2 pins on the M Top 2 pins on the ‘S’.
  • Panel Disassembly required.  (Note during warranty period.)  A simple Forward Bias diode check will cause the diode to illuminate if it is good. Check any pin on the right to any pin on the left.
TESTING ONE LED
TESTING TWO LEDs
LOCAL DIMMING
  • The picture below shows a relationship between the LEDs reaction to real time video on the screen.
  • A good example shown by A, B, C and D show the dark areas of the screen.  As can be seen by the backlight LEDs, they are dimmed out in the same area.
  • To see a representation of the “Local Dimming” look on the Customer’s Menu, turn on Local Dimming Demo.
GLOBAL LED BACK-LIGHT BRIGHTNESS CONTROL CIRCUIT {Click on picture to Enlarge}
TESTING THE BACK-LIGHT BLOCKS
Posted By: FRANK at 05:17
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