how to test lcd led backlight?

[budm]

Re: how to test lcd led backlight?

The printing on the bottom is something like K8CD8C111???? If you can get the number then you can look up the spec sheet.
"Next project:

We can establish a Data Base for all kinds of LED screens.... pins layout .... how many LEDs ......what's kind of LED .......V and A they used....."
If you cannot get the spesheet then you will not know the current handling, color temprature, viewing angle, etc.

[budm]

Re: how to test lcd led backlight?

That 819mV (it is shown on the meter in reverse polarity in that test mode, it test the two legs of the DUT under two conditions, forward and reverse, look at the symbol on your display) got to be some kind of protection diode, there is no LED with that low Vf that I know of, or that meter is doing something funny. I think you need to understand what the meter is showing and how to read the result.

"The tester thinks have two diodes inside. And it is, first Blue diode(2.61V) and dropping with yellow diode (at 819mV) will give the almost white color.......But they put the symbol wrong side.....Don't worry, someone wrote that program not perfect, yet" I think you mis-undetand about LED function. I has only ONE LED.

[tom66]

Re: how to test lcd led backlight?

There is only a blue diode in there.

The LED surfaces are coated in CE:YAG or similar phosphor which emits yellow light when blue light hits its surface (fluroscent)

So it will test around 2.8-4V forward voltage when good, at If=1mA. (Higher If, greater Vf.)

[Peter Chiu]

Re: how to test lcd led backlight?

The $18.00-wonderful tester-a must have toy.
The tester thinks have two diodes inside. And it is, first Blue diode(2.61V) and dropping with yellow diode (at 819mV) will give the almost white color.......But they put the symbol wrong side.....Don't worry, someone wrote that program not perfect, yet

Pic 1: I tested with a red LED


.....What is the P/N printed on the bottom of the LED?....
Hard to read....but just collect them, that was an old stocks. From now on , I will put Penal No. model No.

Next project:

We can establish a Data Base for all kinds of LED screens.... pins layout .... how many LEDs ......what's kind of LED .......V and A they used.....

Pic 2,3: A yellow LED.

A refreshment (From Wi Ki):

There are three main categories of miniature single die LEDs:
Low-current: typically rated for 2 mA at around 2 V (approximately 4 mW consumption).
Standard: 20 mA LEDs (ranging from approximately 40 mW to 90 mW) at around:
1.9 to 2.1 V for red, orange and yellow,
3.0 to 3.4 V for green and blue,
2.9 to 4.2 V for violet, pink, purple and white.
Ultra-high-output: 20 mA at approximately 2 V or 4–5 V, designed for viewing in direct sunlight.
5 V and 12 V LEDs are ordinary miniature LEDs that incorporate a suitable series resistor for direct connection to a 5 V or 12 V supply.

reference:
http://www.electronicsweekly.com/new...kages-2008-08/

http://spectrum.ieee.org/semiconduct...ds-dark-secret

http://www.ledsmagazine.com/articles...s-domains.html


This proof H J Round is the first one:
The first-ever report of light emission from a semiconductor was by the British radio engineer Henry Joseph Round, who noted a yellowish glow emanating from silicon carbide in 1907. However, the first devices at all similar to today’s LEDs arrived only in the 1950s, at Signal Corps Engineering Laboratories, at Fort Monmouth, in New Jersey. Researchers there fabricated orange-emitting devices; green, red, and yellow equivalents followed in the ’60s and ’70s, all of them quite inefficient.

https://www.badcaps.net/forum/showth...t=45234&page=4

Which I posted #68 and nobody believe me.......Like they don't pay attention to the H J Round ( look the years gap about 40 years late)....all because he is not famous as Guglielmo Marconi ( the wireless radio)......

[budm]

Re: how to test lcd led backlight?

What is the 819mV VF, the protection diode?
What is t he P/N printed on the bottom of the LED?

[Peter Chiu]

Re: how to test lcd led backlight?

How to test backlight LED ?...............let's go.....

Pic 1: Look that parts-No.
Pic 2: LEDs.... I took out yesterday.
Pic 3: You can use swab to pick the LED, with help of month-water.
Pic 4: Taped on the tester.
Pic 5: read out the information.
Pic 6: sorting....

[Peter Chiu]

Re: how to test lcd led backlight?

So....so...... beautiful voice, but xxx- video- MTV ,I don't like ....so let's play this one..... Before I get banned.....
https://www.youtube.com/watch?v=ZnI-WKYqp3E.......I need Viagra for that...

How to change LEDs.........
1. Solder iron
2. Hot air gun
3 Oven bake (BBQ)
4 My favor... gas touch.............. collect,sort,and reuse all the LEDs

Next .....I will teach you ,how to test and group them... in case U need one...... because different TV use different LEDs...................most important thing is current......next project......

PS: collect as many LEDs as u can (damper dive)........ we gonna use for making a car head light...........

[keeney123]

Re: how to test lcd led backlight?

Love the LED videos.

[Peter Chiu]

Re: how to test lcd led backlight?

The 65 Lincoln ...Wow ....you're GOOD!


Today, we are very happy, we have our special guests from British …..Round and his cat ...welcome to our show.......

Background music..also from British......one of my favorite songs......
https://www.youtube.com/watch?v=dzXcyUJjJD4


...... A........action.......

First question: Why your cat has no whiskers?
Round: I used them all.
Question : What kind of materials need to use.....to have light?
Round : I just pick up rocks in my backyard.
Question : Do you know ,you change the whole TV industry!
Round: Pardon me, what is TV?? ....And ...And ..I...I.... just a assistant for Marconi......
Question : Final one. Do you know, how to test LED?
Round: ...(Happily)...... I know this one .....with my cat.

.......................Cut..................

...........................The Founder father of the LED......................................

If someone ask me....Who invented the LED... I would say H. J. Round
If you say is Viking or Russian, I have no argument, too.

https://www.youtube.com/watch?t=20&v=8quZrUcRFlw

This is USA movie..... Sorry! …..They did forget …..H. J. Round....... they put him in Electroluminescence (EL) categories.................not fair...........But we will always remember his Cat's-whisker detector........

http://lighting.com/how-leds-are-made/
https://www.youtube.com/watch?v=CAgRF8TibJ0

This is my version of Cat's-whisker detector........with HV CCFL tester... tips put a piece of Kanthal wire.......go to my backyard..... ZAP.....the scorpion... see if any Fluorescent light come out.......If I win Nobel Prizes, I would donate to Badcaps.net......


Qusetion : Who invented the LED
Jose's answer : Creo que tal vez chino.

[keeney123]

Re: how to test lcd led backlight?

Well done it looks beautiful. Love the video and the 65 Lincoln.

[Peter Chiu]

Re: how to test lcd led backlight?

Back to the {how to test lcd led backlight?} .....Are u ready!......OK ......let us ...R....R..O...C..K.........
Background music....We gonna use this https://www.youtube.com/watch?v=09R8_2nJtjg

LG 55LN5400-UA.... EAY62810701 (3PAGC10124A-R) Power Supply / LED Board.... EBT62359788 (EAX65049104(1.0)) Main Board.

LED screen's connector marked (LED- LED+ LED+ LED-) is easy enough.
first group (top) LEDs 48 LEDs ( back....led- , blue.......led+)
second group (bottom) LEDs 36 LEDs ( white.......led- , bule.......led+) Total 84 LEDs

Let's rock with this LG-55' LED-2/2013-screen has 4 wires connector -BD9483F drived-84 LEDs-divided by two groups -TV, which I found in dumpster.......

https://cdn.badcaps-static.com/pdfs/...a8607cbf1a.pdf

The LED-screen-light works good ! So I destroy it with 110AC . Now, one LED is blow out, another LED is no light but look OK. Screen won't come on anymore.........

Simulation Case 1: TV come in with no backlit...Pic, sound is OK

Solution: Open LED screen, use CCFL tester find two LEDs not work.

......After change two LEDs ......... YYYY...EE......S.............. it work.....

Theoretically: One LED not work , the whole LED screen won't light up.........

I forgot the most importance thing: Penal No:LG LN54M550060 V12

Next project:

Isn't that a beautiful one (picture last one,from Samsung 50' LED TV.).

[keeney123]

Re: how to test lcd led backlight?

Thanks for help...... But,.... too dangerous to put a CAP or resistor there....

Trying to do .......like......half wave rectifier

Hint:
If a circuit is predominantly inductive, we say that its power factor is lagging (because the current wave for the circuit lags behind the applied voltage wave). Conversely, if a circuit is predominantly capacitive, we say that its power factor is leading. Thus, our example circuit started out with a power factor of 0.705 lagging, and was corrected to a power factor of 0.999 lagging.

REVIEW:
Poor power factor in an AC circuit may be “corrected”, or re-established at a value close to 1, by adding a parallel reactance opposite the effect of the load's reactance. If the load's reactance is inductive in nature (which is almost always will be), parallel capacitance is what is needed to correct poor power factor.

Next project preview:

How to modify The CCFL Tester , amplifies the 40 kHz signal as a Ultrasonic welding machine...... to weld the tab back to the LCD screen (LCD screen common connector's problem) ....we need ....pressure,temperature,skill, and Ultrasonic melting power...
https://www.youtube.com/watch?v=dYHPKxijz1A

Usually power factor is used in businesses that have a lot of inductive motors. The meters only see apparent power not real power, so they get charged more then they are actually using. These companies will use large Capacitors to counter act the inductive resistance with capacities resistance leaving only the actual resistance that is in the circuit.

[Peter Chiu]

Re: how to test lcd led backlight?

For Mains Isolation--Again Cheap Cheerful, --with possibility of voltage customisation (within limits)

Two std low-voltage transformers--Say a pair of lighting Toroids or whatever you've got around--providing they the same O/P voltage, and the same/similar VA rating/size.....

Connect the first Secondary to the Secondary of the Second.

Connect the First Primary to the mains...

You'll have an isolated 240V (Assuming mains is 240V) at the primary of the second.....

I use two 650VA toroids like this--as a Mains Isolation Transformer to run sets from--Works pretty well!


Thinks for the good tip ....... two donuts (isolate-transformer) gonna look nice.


Find 2 microwave HV transformers (which a lots people rewired to make welding machine).
Put two primary coil together and weld it back and u have 10A isolate-transformer (higher efficiency) but it's kinda heavy.

How is your project doing ? I would like to know,one more way to light up whole LED screen penal (directly from AC outlet cheap and simple like u idea before )....... as household light source......cheap and e-recycle.........

[Alastair E]

Re: how to test lcd led backlight?

Hmm--Uncle Walt's been working Overtime again......

[Peter Chiu]

Re: how to test lcd led backlight?

...... acting as an antenna, only capacitive parasitic factor of diode matters (~50-1000pF).

That's why the sinewave has a little bit distortion....... Good......

Near the Transformer, two transistors on each side are D1816, D1816( 2sd1816 both are NPNs ) the two small ones are 8550ss(NPN) and 8050ss(PNP)






I know ,we gonna have a circuits diagram very quick........
I double- check still the Transister are D1816, D1816

[tom66]

Re: how to test lcd led backlight?

Thanks for help...... But,.... too dangerous to put a CAP or resistor there....

Trying to do .......like......half wave rectifier

Hint:
If a circuit is predominantly inductive, we say that its power factor is lagging (because the current wave for the circuit lags behind the applied voltage wave). Conversely, if a circuit is predominantly capacitive, we say that its power factor is leading. Thus, our example circuit started out with a power factor of 0.705 lagging, and was corrected to a power factor of 0.999 lagging.

REVIEW:
Poor power factor in an AC circuit may be “corrected”, or re-established at a value close to 1, by adding a parallel reactance opposite the effect of the load's reactance. If the load's reactance is inductive in nature (which is almost always will be), parallel capacitance is what is needed to correct poor power factor.

Next project preview:

How we modify The CCFL Tester , amplifier the 40 kHz signal as a Ultrasonic welding machine...... to weld the tab back to the LCD screen (LCD screen common connector's problem) ...

No....
It's because you have essential nil current flowing thru the diode (1Meg+air losses), so the P-N junction doesn't really work.
It's acting as an antenna, only capacitive parasitic factor of diode matters (~50-1000pF).

[budm]

Re: how to test lcd led backlight?

Can I get just straight shot of the bottom side of the board?
The transformer output drivers look to be just the Two power MOSFETs and the tunning cap (Brown Polyester film cap) Royer Osc circuit. Q1 (PNP?, P/N?) control the ON/OFF GATE bias Voltage (through R6, 1K2 Ohms?)
The 8-pin IC is not 555 because pin 8 (VCC pin for 555) of that IC is connected to circuit GND (Negative GND).
If you want to lower the HIGH Voltage output , then you need to lower the B+ to the output, the B+ id fed through that TOROID inductor.

[Peter Chiu]

Re: how to test lcd led backlight?

Thanks for help...... But,.... too dangerous to put a CAP or resistor there....

Trying to do .......like......half wave rectifier

Hint:
If a circuit is predominantly inductive, we say that its power factor is lagging (because the current wave for the circuit lags behind the applied voltage wave). Conversely, if a circuit is predominantly capacitive, we say that its power factor is leading. Thus, our example circuit started out with a power factor of 0.705 lagging, and was corrected to a power factor of 0.999 lagging.

REVIEW:
Poor power factor in an AC circuit may be “corrected”, or re-established at a value close to 1, by adding a parallel reactance opposite the effect of the load's reactance. If the load's reactance is inductive in nature (which is almost always will be), parallel capacitance is what is needed to correct poor power factor.

Next project preview:

How to modify The CCFL Tester , amplifies the 40 kHz signal as a Ultrasonic welding machine...... to weld the tab back to the LCD screen (LCD screen common connector's problem) ....we need ....pressure,temperature,skill, and Ultrasonic melting power...
https://www.youtube.com/watch?v=dYHPKxijz1A

[tom66]

Re: how to test lcd led backlight?

Diode will be predominantly capacitive with no output termination. Cannot measure like that.

[Peter Chiu]

Re: how to test lcd led backlight?

The CCFL tester more accurate..... The oscillator is at about 38K HZ. (The same as most LCD TV CCFL ballast's frequency.)

DIP 8 pins IC (they erased) can't see the No.
.....(At the price range $12 ).......Maybe...LM555(As an oscillator +LM78L05 + four transistors (two pair NPN and PNP)to oscillate the HV transformer.

Picture 2: put SF(super fast ) diode still sinewave... HELP! PLS.....

Open the PICs take long time what else we can do....??....