how to test lcd led backlight?

[budm]

Re: how to test lcd led backlight?

"....This is fun.....you can light up almost all LEDs , by maneuver the distance( not discretely touch ....near then move away ).
playing with ..... the arc.....the Plasma.......{ feel like.... Nikola Tesla play with his Tesla coils....}" That radiated high frequency AC will light up Fluorescent lamp but not the LED.

[Peter Chiu]

Re: how to test lcd led backlight?

I did not know ,U can light up CCFL light buld.... Good....Good .... useful Tips
Because neon lamp too small to find it... all the time, then I look at the red light on power stripe,I know I find one,but .....too much effort to.......Thank you very much...
May God bless America.

Next project:
How to use EXT(external) PWN signal to do the LED dimmer control........and use as LED screen tester II.......

[budm]

Re: how to test lcd led backlight?

High Voltage probe:
https://www.badcaps.net/forum/showth...x+dx-40l261a12

[Peter Chiu]

Re: how to test lcd led backlight?

....... I see that the CCFL is lit up partly on one of the winding. The good winding will light the lamp brightly. I remove the transformer, and sure enough, it has burnt winding.
So this is a new trick for finding bad inverter transformer.......
? Aurora ???
Exactly happen to me!!! This phenomenon can apply to (the LEDs section) too..... Amazingly.... the power of the nature....probably we can use proton or electron to light up LEDs.....or tasla ball or maybe super NOVA comic rays.......or just close to {Electricman-2} will light up the LEDs ....I knew electric static will light up fluorescent light, when I was a teenage, I hided in the cloth closet, used wool sweater to rub the tube ...and it light up.......


The vacuum - gas or mercury filled -CCFL-or neon light... I knew that already.
But for a semiconductor- solid state- PN junction-LED, I just learn today.

[Alastair E]

Re: how to test lcd led backlight?

....... I see that the CCFL is lit up partly on one of the winding. The good winding will light the lamp brightly. I remove the transformer, and sure enough, it has burnt winding.
So this is a new trick for finding bad inverter transformer.......
? Aurora ???
Exactly happen to me!!! This phenomenon can apply to (the LEDs section) too..... Amazingly.... the power of the nature....probably we can use proton or electron to light up LEDs.....or tasla ball or maybe super NOVA comic rays.......or just close to {Electricman-2} will light up the LEDs ....I knew electric static will light up fluorescent light, when I was a teenage, I hided in the cloth closet, used wool sweater to rub the tube ...and it light up.......

The vacuum - gas or mercury filled -CCFL-or neon light... I knew that already.
But for a semiconductor- solid state- PN junction-LED, I just learn today.

Err--

Wot on EARTH have You been smoking tonight!!--Some of Heisenburg's finest I reckon

[Peter Chiu]

Re: how to test lcd led backlight?

After 4 hours research.... still no answer.....
1. Why did not burn out the LEDs which I think so too.
2.When any side of LEDs section, connected to the CCFL tester's ground will light up.. ........ Is the leaking voltage from real ground ,enough to breakdown the PN junction 's Bias voltage 0.56v

http://en.wikipedia.org/wiki/P%E2%80%93n_junction

there is a non-linear relation between voltage and current as shown in the picture ,In region 1, there are free ions that can be accelerated by the field and induce a current. These will be saturated after a certain voltage and give a constant current, region 2. Region 3 and 4 are caused by ion avalanche as explained by the Townsend discharge mechanism.

Saturate certain voltage and give a constant current.... may be this is the answer..?......

I can light up LEDs with + - or - + means non polarized....or is the CCFL tester actually is AC (I mean no HV dieodes inside , need to open the Tester to find out ???

........un....FIN....

[budm]

Re: how to test lcd led backlight?

White LED Vf (Junction Voltage) is between 3~4V range. Vf range depends on the current, so the LED Vf chart spec.
http://www.maximintegrated.com/en/ap...ex.mvp/id/3070
Typical silicon diode has Vf of 0.6~0.7V
Is that arcing in picture #2?
Check the current draw.

[Peter Chiu]

Re: how to test lcd led backlight?

This is better than (The Most Unbelievable event in the universe)...The Big Bang





Oh......... My sweet Lord............George Harrison......
https://www.youtube.com/watch?v=HI8XY5BX_CE


Even I hammer down one LED

They still light the rest LEDs ....BY high voltage jumping?.....(in picture 2)


......Should I hammer down more LEDS and give back the report.......

After about 20 mins

Oh ......YYY...E...SS....Yes......Yes....... (in picture 3)


.................We Are The Champions............................Queen..............
https://www.youtube.com/watch?v=04854XqcfCY


By the way, The CCFL tester exactly the same one in this video
https://www.youtube.com/watch?v=sfVkRiDGewA

Tomorrow's project:

Test different kind of LEDs back-light ( direct refection) screen...........

[Peter Chiu]

Re: how to test lcd led backlight?

I know, I got too excited, my pituitary give myself too much morphine.
As a ADHD-senior citizen-electronic enthusiast I apologize for my misbehavior.

Ok.... let's rock ........

The LED Screen divided to two sections top 3 line LED strips, bottom 4 lineLED strips.
Picture 1 ...I test with original Samsung power supply @ 1us so it's about 2Mhz/374V
Picture 7 The CCFL tester @20us so 50khz- sine wave-voltage out of my scope's range.
Picture 6 Just light up 1 LED.
Picture 3 only connected the CCFL tester black ground wire.
Picture 4 light up all the LED screen.


See in the picture, I cut my hand.......so I am in deep (The Moody Blues).....

........to be continued.........

[budm]

Re: how to test lcd led backlight?

Pic 7: https://www.badcaps.net/forum/attach...1&d=1427996444

I am surprised that you did not damaged at least the input circuit of the scope.
I see that all the pictures show arcing from the tip of the CCFL tester to the LED connecting wire, is that right? And if you make the tip to have direct electrical contact to the wire, then did you damage the LEDs?

[Peter Chiu]

Re: how to test lcd led backlight?

Picture 6 Just light up 1 LED
I did try directly contact just one LED still OK . In reality, the brightness isn't bright enough.
The CCFL tester should use 2A 12v but I use 1A 12v( next time put a 3A/30v power supply or (a LM317 adj-voltage IC) will be fun.

.......arcing from the tip of the CCFL tester to the LED connecting wire......
That's why did not burn ,I use (the distance of the gap) as the current limitation.

Next project 1:
use total current to estimate how many LEDs in one section.
Next project 2:
Put a HV diode on the tips of the CCFL tester ,To distinguish + section's LEDs or -section's LEDs

By not open the LED screen and we will know the answer (total number of the LEDs and how many sections LEDs the LED screen has and each connector wire's funtion? )....

[budm]

Re: how to test lcd led backlight?

"use total current to estimate how many LEDs in one section" current draw will not tell you how LED or diode are in series, its the total Vf that can give estimate how may active device is connected in series.
You can easily prove that using 6 Diode in series with small current limiter resistor then measure the total Vf for the 6 diode, you should see around 3.6V, please notes that Vf varies with If.

[Peter Chiu]

Re: how to test lcd led backlight?

Very good suggestion ! That will be more accurate.


I need to modify my CCFL tester to veritable HV . Maybe from Oscillator or input supply voltage.

[budm]

Re: how to test lcd led backlight?

Open it up to see what are inside that tester. It is still too dangerous due to high Voltage out put.

[Peter Chiu]

Re: how to test lcd led backlight?

By the way, The CCFL tester exactly the same one in this video

he already open .....Me too, will take picture ......tomorrow......
https://www.youtube.com/watch?v=sfVkRiDGewA


Picture 1 ...I test with original Samsung power supply @ 1us so it's about 2Mhz/374V

Sorry, should be 1/(1us*4)=250kHz stead of 1us*2= 2MHz oh... sorry, my bad!....

[keeney123]

Re: how to test lcd led backlight?

I believe the static breakdown voltage of transistor with a silicon base are between 2500 and 4500 volts. This voltage can be created on a person walking across a wool carpet in low humidity. More fragile low current uni-junction FETs can be taken out with 100 volts static. This can be caused by rubbing a probe (in this case a medical research probe) against a the back of a plastic covered chair. BudM I like your new design it has promise.

[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....??....

[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?

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

[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.