how to test lcd led backlight?

[budm]

Re: how to test lcd led backlight?

They are selling the whole strip not the individual LED, Shopjimmy is also selling some replacement strips now too.

[Peter Chiu]

Re: how to test lcd led backlight?

One of the LEDs I take out from the board ,now.and,I take picture again.
When I push test button, the LED will blink twice then the the readout....

For BUD M... yes , but you drew the diagram mean SHORT ( in DC, but they probably use 1k-100k hz to test the pin because they can test ESR...

[budm]

Re: how to test lcd led backlight?

The meter is doing its auto test routine by reversing the probes automatically just like when you do the test manually with your meter by testing the DUT in both direction.
Just hook up two diodes as shown in my picture then you will understand what your meter is doing.
Just use your DMM to do the diode test both direction on that LED to see what it shows on the DMM also.

[Peter Chiu]

Re: how to test lcd led backlight?

No, exactly happen like #70 readout, I will use scope and see what happen.....tomorrow...

but you drew the diagram mean SHORT ( in DC, but they probably use 1k-100k hz to test the pin because they can test ESR...

By the way.....the tester is GM328 transistor tester \ ESR meter \ LCR meter \ Cymometer( Frequency counter)\ square wave generator......... most is the firmware (software) do the job....

[budm]

Re: how to test lcd led backlight?

"but you drew the diagram mean SHORT" No, it is not. I think you need to read up on electronics theory! iF YOU THINK ANTI-PARALLEL connection of the two diode is short, you have more learning to do.
As I said, hook two diode as shown and use the DMM to read the Vf in both directions and see what you get.
The 100KHz is used for ESR AC resistance testing, nothing to do with Vf testing.
When you test the junction of the semi, does your DMM in diode mode put out 100KHz for testing the Vf, of course not.

" most is the firmware (software) do the job...." Like I said it does the test routine by applying the reversing testing automatically, what do you think do when you test semiconductor, you test it in both directions.
How do you think it knows when you stick a bipolar transistor and it can tell you if it is PNP or NPN? How do you do with your DMM to figure out if it is PNP or NPN?
BTW, you DID NOt hook up the diodes as shown and tested in pin 2 and pin 3 of the tester as I suggested, right? or Tested them with your DMM.

[Peter Chiu]

Re: how to test lcd led backlight?

Sorry... Sorry..my bad ..... I did not pay attention to that , I was here and there take pictures, take out SD card and put it back.........yes , when you use multimeter is 0.5V and the other side is 0.5V .....but when I put on DC power supply ,they shorted right away...Yes I really don't know why......although I did graduate Electronic Engineering(double E).
Oh.....Oh...I remember, it is reverse voltage readout.....too late...... I lose.....I really think..... how could you ask so simple question to me ... teacher gap a handful scr triac pnp npn ujt mosfet ...I am the only guy pass the test. By use mouth-water I can distinguish EBC each legs ............my apology...........

[budm]

Re: how to test lcd led backlight?

"but when I put on DC power supply there shorted right away..." Why would you do that? The diode will try to maintain Vf of about 0.6V, so what do you expect.
May I ask, did you take any basic electronics theory class?
Read this what the anti-parallel diode connection can be used for and how it is used.
http://www.electronics-tutorials.ws/...-circuits.html

"Yes I really don't know why......although I graduate Electronic Engineering(double E)."
What the heck do they teach these days? No hands on in the labs? I mean you look at the circuit you can see what is going to happen. The power supply has output impedance, then you have diodes connected to the output.

[keeney123]

Re: how to test lcd led backlight?

BudM are you sure the 0.826 Volt reading of the device is coming from a protection diode built into the device or is this protection diode built into the LED? Understand BudM the higher the level of theory the bigger the mistakes. Like sometimes not being able to see the forest through the trees.

[Peter Chiu]

Re: how to test lcd led backlight?

I been build frequency counter,Apple II, TTL logic analyzer,Constant current control power supply, Oscilloscope,frequency counter ......all from components and made my own PCB ...I learned Assembly language , COBOL and FORTRAN and I am airline , hospital equipment maintenance manager for a long time.... been trained by UK engineers. And now I still own a electronic company , I use multimeter and Oscilloscope for 40 years........In real world , that circuit not exist, will shorted. I only see two zener diodes put together......I am not very sharp person , you can find my neglect all the time (I have ADHD), like I always find my employees troubles ....be nice...... We ALL love Electronics.......Hoop! In the future, you can find the genuine side of me....

[budm]

Re: how to test lcd led backlight?

".In real world , that circuit not exist, will shorted I only see two zener diodes put together" What do you mean that clipper circuit does not exist? You are joking right? Again, shorted?
Want to learn?
http://www.muzique.com/lab/zenmos.htm
http://www.giangrandi.ch/electronics...-clipper.shtml
http://sound.westhost.com/articles/soft-clip.htm
https://cdn.badcaps-static.com/pdfs/...e96127937c.pdf


http://www.musicworks.ca/diy/how-make-fuzzbox

[budm]

Re: how to test lcd led backlight?

BudM are you sure the 0.826 Volt reading of the device is coming from a protection diode built into the device or is this protection diode built into the LED? Understand BudM the higher the level of theory the bigger the mistakes. Like sometimes not being able to see the forest through the trees.

He can easily simulating the reading by connecting the Diode and the LED as shown or verify that with his DMM.
That Diode is probably for reverse polarity protection since the most White LED can only handle about 5V reverse voltage, with the Diode in place, the max reverse Voltage across the LED will be only about 0.80V

If you read this in post 73 about how he thinks it has TWO LEDs to produce Whit lights "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"
How can the so call Yellow diode which shows on the meter as anti parallel connection will ever light up when you only apply the current flow in one direction (DC). So I have been trying to explain that it only has ONE LED!

[Peter Chiu]

Re: how to test lcd led backlight?

Never be afraid to ask questions....Anybody know more than me, are my teachers....
But, small signals and HF is totally different storys...I did fall first time on my hf antenna theory.... all is advance mathematics and mathematics. Sorry! I still at my office. When I go home ,I don't play computer at all....I need to give time to my family ...... see you tomorrow ...

[stj]

Re: how to test lcd led backlight?

could be a reverse diode,
some early phillips leds on the star heatsink had a reverse led diode - they used a visible red led so you could tell if the polarity was wrong.

[budm]

Re: how to test lcd led backlight?

It is a matter of applying what you want the circuit to do. Diode is not made just for rectification only, it can be used as switch also for example.

"yes, when you use multimeter is 0.5V and the other side is 0.5V " So how does it display on your tester?

How about another application, Voltage protection for OP-AMP?
https://cdn.badcaps-static.com/pdfs/...921fff160b.pdf

BTW, I am still learning EVERYDAY!

[Peter Chiu]

Re: how to test lcd led backlight?

It's a FUN project.....We gonna built a car's head lights.....and LED screen tester ...will be delayed...
First: Ordered parts are on the way......Second: I need to study, the stuffs, I've given back to the teachers...

I am so....so...SORRY!......I did not pay a attention to your idea ( I was at the office and Friday night and I's hungry)….....BUD M …..and, you are right, again.... .....(look picture)......look like it did has a protection diode inside........We all love Electronic......that keep me out of street, drugs, make millions for me, my job, my career, my every thing. (sound like this https://www.youtube.com/watch?v=Fcd3XuQwDQQ).......... I just try to feedback somethings to the society.........with minus salary......and As big heart as you guys doing.......so... take it easy........

Would you Please teach me this.......No time limit just for study....I will try it, also.....It's fun...
Question 1: What is the voltage read out ,if you change to two Schottky diodes.
Question 2: What is the voltage read out ,if you change to two Ideal Diodes
Question 3: What is the voltage read out ,if you change to two Zero Bias Schottky Detector Diodes, two resonant-tunneling diodes or two Tunnel diodes .
Question 4: What is the voltage read out ,if you connected series or parallel to DC5V , AC 5V and the high (or microwave) frequence.

Two capacitors or resisters put in series or parallel together, the values , I still make mistakes …. all the time........I'm not straight A student like most Asia's student do....I was a party boy....I's in a Band (called {120DB} U know what that means)........and I graduated by use cheating note …................. have fun.......

Never stop learning studied:
The Schottky diode
(named after German physicist*Walter H. Schottky); also known as hot carrier diode is a semiconductor diode*with a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.
When forward current flows through a solid state diode there is a small voltage drop across its terminals. A silicon diode has a typical voltage drop of 0.6 to 0.7 volts, while a Schottky diode has a voltage drop of 0.15 to 0.45 volts. This lower voltage drop can be used to give higher switching speeds and better system efficiency.
A tunnel diode or Esaki diode is a type of semiconductor that is capable of very fast operation, well into the microwave frequency region, made possible by the use of the quantum mechanical effect called tunneling.

The Tunnel diodes
were first manufactured by*Sony*in 1957[2]*followed by*General Electric*and other companies from about 1960, and are still made in low volume today.[3]*Tunnel diodes are usually made from*germanium, but can also be made from*gallium arsenide*and*silicon*materials. They are used infrequency converters*and*detectors.[4]*They have*negative differential resistance*in part of their operating range, and therefore are also used asoscillators,*amplifiers, and in*switching circuits*using*hysteresis.

A*resonant-tunneling diode*(RTD)
is a*diode*with a resonant-tunneling structure in which electrons can tunnel through some*resonant*states at certain energy levels. The*current–voltage characteristic*often exhibits*negative differential resistance*regions.
All types of*tunneling diodes*make use of*quantum mechanical tunneling. Characteristic to the current–voltage relationship of a tunneling diode is the presence of one or more negative differential resistance regions, which enables many unique applications. Tunneling diodes can be very compact and are also capable of ultra-high-speed operation because the quantum tunneling effect through the very thin layers is a very fast process. One area of active research is directed toward building*oscillators*and switching devices that can operate at*terahertz*frequencies.[1]

CNTFETs
show different characteristics compared to*MOSFETs*in their performances. In a planar gate structure, the p-CNTFET produces ~1500 A/m of the on-current per unit width at a gate overdrive of 0.6 V while p-MOSFET produces ~500 A/m at the same gate voltage.[23]*This on-current advantage comes from the high gate capacitance and improved channel transport. Since an effective gate capacitance per unit width of CNTFET is about double that of p-MOSFET, the compatibility with high- k gate dielectrics becomes a definite advantage for CNTFETs.[21]*About twice higher carrier velocity of CNTFETs than MOSFETs comes from the increased mobility and the band structure. CNTFETs, in addition, have about four times higher transconductance.[citation needed]

Metal–oxide–semiconductor structure
The traditional metal–oxide–semiconductor (MOS) structure is obtained by growing a layer of*silicon dioxide*(SiO2) on top of a silicon substrate and depositing a layer of metal or*polycrystalline silicon*(the latter is commonly used). As the silicon dioxide is a*dielectric*material, its structure is equivalent to a planar*capacitor, with one of the electrodes replaced by a semiconductor.

Zero Bias Schottky Detector Diodes

file:///home/a/Desktop/badcaps%20pic/41115/AV02-1377EN%252C0.pdf

kinda late. I not supposed to come to office today. But company has a lot things need to be going ...I need to earn my coins...one by one.... . ... going to GYM soon…....see you guys …..lunes.......

[keeney123]

Re: how to test lcd led backlight?

He can easily simulating the reading by connecting the Diode and the LED as shown or verify that with his DMM.
That Diode is probably for reverse polarity protection since the most White LED can only handle about 5V reverse voltage, with the Diode in place, the max reverse Voltage across the LED will be only about 0.80V

If you read this in post 73 about how he thinks it has TWO LEDs to produce Whit lights "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"
How can the so call Yellow diode which shows on the meter as anti parallel connection will ever light up when you only apply the current flow in one direction (DC). So I have been trying to explain that it only has ONE LED!

I see what you are saying. If it is a DC voltage it will light in one direction and block in the other direction up to 5 volts before burn out. I do not know how the inside of his tester is wired, but it would make sense to have a protection diode or LED in the reverse direction to protect the circuit being tested. The tester could be connected to reverse the polarity by utilizing a multi-vibrator or 555 timer circuit but the meter should show a reverse polarity on its readout. Of course if there is a processor and rom, etc. It could have a program that looks out on the input lines through a A to D converter to determine what it is connected to in order to take a reading. Is this a meter he is using a device he is building or something that was bought on the market?

[keeney123]

Re: how to test lcd led backlight?

"Two capacitors or resisters put in series or parallel together, the values , I still make mistakes …. all the time........I'm not straight A student like most Asia's student do....I was a party boy....I's in a Band (called {120DB} U know what that means)........and I graduated by use cheating note …................. have fun......."

Perhaps you should had not partied so much and used cheating note because now you want to invent new devices and you missed out on doing the hard work that is required to do the things you are planning. I guess it is never to late to learn.

[stj]

Re: how to test lcd led backlight?

Is this a meter he is using a device he is building or something that was bought on the market?

he's using this:
http://www.mikrocontroller.net/artic...ansistortester

you may want to put it in a translator.
they are being mass produed in china for about $20 on ebay.

[keeney123]

Re: how to test lcd led backlight?

he's using this:
http://www.mikrocontroller.net/artic...ansistortester

you may want to put it in a translator.
they are being mass produed in china for about $20 on ebay.

Thanks stj. Seems like a lot of product for $20.

[budm]

Re: how to test lcd led backlight?

The meter does the auto testing in both polarity that is how it can determine unknown transistor to show you if the transistor is PNP or NPN, same way that you test the transistor manually to check the EB, EC junctions, same when it test the diode.