how to test lcd led backlight?

[Peter Chiu]

Re: how to test lcd led backlight?

$ 40.00 is the cost of manufacturing of the products in mass quantities..... not count the R & D and software development. ...to put it another way......is your cast to built each one.

Ex: Like $ 300.00 EEprom writer will cast about $ 40 hardware but firmware needs to update all the time....

First I needs to built a prototype and numerous times to modifier them and find all the adapter for each TV. (each adapter sold separately). patent pending....Dealer....on and on.....I estimate will 10 time more market than ESR cap tester or (if you that old) CRT- rejuvenator..

[keeney123]

Re: how to test lcd led backlight?

Yes, I know. I will work on my power supply for testing LED and will post the result after I am done.

Yes, this is what is needed as having it in circuit involves feed back loops. So then if you know the LEDs are good one can then just concentrate on the driver circuit. Thanks BudM for doing this as I think it will make a lot of people's life's easier.

[budm]

Re: how to test lcd led backlight?

The questions are, without opening the screen how would you know:
1) How many LED strings are inside the TV
2) How many LEDS are in each string, some LED may have two or more LEDs in one body.
3) How the LED strings are connected together, series or parallel, or series-parallel combination.
So unless you have LCD panel details spec sheet you will not know how they are connected, seeing only one pair of wire is easy to figure out, but see 4 pair of wires or more coming out of the panel is another story.
Have some one build a bunch of black boxes with many combination of LEDs connected with a buch of wires coming out and give them to you without giving you the clue as to what are inside boxes and have you figure them out using your test box to identify how many LEDs are inside and how they are connected.
I am sure your professor did you give the student in the lab the black boxes with wires coming out and ask them find out what is in the box using the test equipment to find out what is inside the box.
The connector interface alone will be a big problem since there is no standard for the connector for the LED driver board.
As far as knowing the current handling of the LED, at this point there is no tools that I know of that can figure out the current handling of the LED without getting the spec sheet form the LED manufacturers.

[stj]

Re: how to test lcd led backlight?

cant you just use a regulated psu with an ammeter inline to test the strings for open or short sections?

[budm]

Re: how to test lcd led backlight?

cant you just use a regulated psu with an ammeter inline to test the strings for open or short sections?

Yes, just need power supply with low current, 10DCmA will be more than enough and Variable power supply that can go from around 24 to ~200VDC.
The hardest part is to figure out the polarity of the wires coming out from the panel, unless the connectors are labeled with A/K, or +/-, d+/d- then you can spend lots of time figuring out what those 4 wires or 8 wires are, tracing the connection at the circuit board will help when work with unknown. I usually looking at how the board to see how it functions first.
I am sure someone or some tester can do that and find the correct adapter in 10 minutes.

[Peter Chiu]

Re: how to test lcd led backlight?

LED panel details spec sheet is kinda hard to fine .....but only few guys make it actually

LG SAMSUNG-----korea
AOL-----Taiwan
Apex -lots of them ,I don't even know the name --China
Panasonic sanyo sony-Japan

Believe or not that's all, because they low down the price , nobody else will compete with them.

Form news what I hear Sanyo not happy with samsung take most 110' LED TV market... try untied with China flight it back the 120' LED TV for about $ 2000-$3000.....

In the future, by sorting the panel information will be just few kind only, because everybody try to cut conner.......or OEM ...like sony did,,,,,.

.........The hardest part is to figure out the polarity of the wires coming out from the panel......
I think you did teach us use bridge to do it.....then will become non-polarity...

[budm]

Re: how to test lcd led backlight?

LED panel details spec sheet is kinda hard to fine .....but only few guys make it actually

LG SAMSUNG-----koren
AOL-----Taiwan
Apex ---China
Panasonic sanyo sony-Japan
Believe or not that's all, because they low down the cost , nobody else will compete with them.
Form news what I hear Sanyo not happy with samsung take most 120' LED TV market... try untied with China flight it back the 120' LED TV for about $ 2000-$3000.....
In the future, by sorting the panel information will be just few kind only, because everybody try to cut conner........

How is that going to help you finding out how those LED strings inside are connected together, even if you have OLY ONE manufacture, they will have many ways of hooking up the LEDs inside for Edge lit, backlit with local dimming, the size of the screen, etc.

[Peter Chiu]

Re: how to test lcd led backlight?

look EEprom writer from EEV .... he did open one and you can see the design of it .....kinda of Buffer or Darlington transistor or mosfet for switch on and off ...... Ok is like this......I can put any 8 pins Dip EEprom and they will recognize the manufacture and IC no..... I know they read the index or ID first .... but they know you put up side down and not going to burn anyway....some of them has in circuit programming function...

They use microcontroller to store information and each different pin or the timing....roughly about 3000-10,000 each eeproms..ICs....legs pinout. and they can test most TTLs and COMSs too.....

[JeffJ]

Re: how to test lcd led backlight?

Peter, an EEprom programmer that can read a chip id, is different then connecting a string of leds. leds would be considered a stupid device they do not identify them selves and they cannot talk back. I can see Budms issues he raises. There really is no way to identify parallel or series wiring with how many leds. And since these are so sensitive, an assumption could cause more damage.

Lets say one manufacturer sells a diode, i could engineer 1001 ways to use that diode that could never be identified blindly by plugging in a box. And this is exactly what we're faced with.

[Peter Chiu]

Re: how to test lcd led backlight?

This confuse me too, this part still under development ... we can now only know the total current no problem, still needs the blueprint from panel manufacturers ... look back to all that CCFL do you still need to open to see what kind of CCFL inside 80 % we know is U shape or straight and how many CCFLs it is ...by open 100 LED screens we can concussion come similarity.......EX: Samsung LED 55' TV , the LEDs are 7983340.... 33 means 3.3v 40 ..means 40ma and we know from 2015-2018 they use this kind of LEDs /by total current ....we will know exactly how many they used
By the way that's my goal to complete...when I finish the prototype I will let everybady know for sure....

[budm]

Re: how to test lcd led backlight?

"but look back to all that CCFL do you still need to open to see what kind of CCFL inside 80 % we know is U shape or straight" once we verify that the inerter board is OK, you still have to open up the panel to inspect the lamp for bad wiring, bad lamp sockets, worn out lamps, etc. Using CCFL tester will not tell you if you have bad wiring at the end of the lamp because the lamp will still light up (high voltage can easily jump the bad connection to light up the lamp) and the main thing about CCFL tester is that it does not have error detection circuit to detect if the lamp is drawing enough current or too much current, or the lamp is actually connected.
Bad lamps:
http://s807.photobucket.com/user/bud...?sort=3&page=1
Beside, the CCFL are connected in parallel separated by ballast caps.

[budm]

Re: how to test lcd led backlight?

"EX: Samsung LED 55' TV , the LEDs are 7983340.... 33 means 3.3v 40 ..means 40ma and we know from 2015-2018 they use this kind of LEDs /by total current" Can you show me the spec sheet of this 7983340? 40mA for HB LED?
Look at the typical current draw:
https://www.badcaps.net/forum/showpo...4&postcount=95

[budm]

Re: how to test lcd led backlight?

EX: Samsung LED 55' TV , the LEDs are 7983340.... 33 means 3.3v 40 ..means 40ma and we know from 2015-2018 they use this kind of LEDs /by total current ....we will know exactly how many they used"
So lets say that they use 10 of them in series, what will the total current draw will be and what is the total Vf will be?

[Peter Chiu]

Re: how to test lcd led backlight?

That is an example....but one CCFL not work... some TV do detect them and go into protection. Why their know ? CURRENT

I will talk to u ,tomorrow. I gonna go .

[budm]

Re: how to test lcd led backlight?

"That is an example....but one CCFL not work... some TV do detect them and go into protection. Why their know ? CURRENT"
Well if you read the 2-second to black thread you will know that, beside I have never see inverter circuit without the error detection circuit to protect itself if the lamp is not connected, or if the lamp is connected and fired up but does not stay conducting, or too much current is being drawn. Your CCFL tester does not have that function to tell if the lamp is good or bad that is why I pointed out about your BLUE BOX CCFL tester that you have.

[keeney123]

Re: how to test lcd led backlight?

Peter Chiu the only way one could build what you are trying to build is to know how each LED string on all TV's have been connected then a program could be written to start out with the lowest voltage lowest current configuration and send a signal out and look for feed back current. The program would have to step through each possible connection until it found the right connection. Of course if you had an open circuit it would never find a connection. One still would have to take the TV apart to test the strings. The only way around taking it apart is if the manufacturer brought the LED connectors to the outside of the TV were one could disconnect the LED string and connect the tester. All of this testing could be done if you had standardization of the LED connectors. This would be up to the manufacturers to get together and create these standards. If they will not do this then the only way is to do it like BudM is doing. It would be impractical to try and find out of all the ways the LED strings were hook up in TV,s. If you want to try to do that I would contact all the manufacturers who make led strings for TV and find out all the various ways they have made them. Of course you are going to get into proprietary patents of the individual manufacturers. So then you would need to go to all the manufacturers of TV's and tell them what you are trying to do. If they agree to give you that information they will most likely ask for a percentage of the profit.

[budm]

Re: how to test lcd led backlight?

Peter Chiu the only way one could build what you are trying to build is to know how each LED string on all TV's have been connected then a program could be written to start out with the lowest voltage lowest current configuration and send a signal out and look for feed back current. The program would have to step through each possible connection until it found the right connection. Of course if you had an open circuit it would never find a connection. One still would have to take the TV apart to test the strings. The only way around taking it apart is if the manufacturer brought the LED connectors to the outside of the TV were one could disconnect the LED string and connect the tester. All of this testing could be done if you had standardization of the LED connectors. This would be up to the manufacturers to get together and create these standards. If they will not do this then the only way is to do it like BudM is doing. It would be impractical to try and find out of all the ways the LED strings were hook up in TV,s. If you want to try to do that I would contact all the manufacturers who make led strings for TV and find out all the various ways they have made them. Of course you are going to get into proprietary patents of the individual manufacturers. So then you would need to go to all the manufacturers of TV's and tell them what you are trying to do. If they agree to give you that information they will most likely ask for a percentage of the profit.

All he has to do is to get lots of screens with all kind of connectors, with many wires for the LED, then figure out the way to find out which wire is for the Anode for which string, and which wire is for the Cathode for which string, then start testing each string to find out which one does not draw current or light up.
Just think about it, if you have 8 wires, how many combination of testing just to locate the correct pair of wire.
Like I said, you treat the LCD panel like and unknown black box with wires coming out and you need to get the right pair first, once you get that right, powering up is an easy part using current limited variable power supply (only about 2W (200V 10mA) power supply is needed) with AMP meter. Standard connector, good luck with that. The whole point of testing is to find out if one or more LED string has open circuit without removing the panel.
I wonder if Peter ever use tube tester, it comes with many switches and socket adapter and big tube pinout charts of just about all the tubes are made and you have to choose correct switch setting, socket after looking at the tube charts.
To solve the problem is to understand what is/are in that black box (LCD panel) and what it needs to work first then you coming up with the solution and tool to power that black box (LCD panel). So ask yourself what do you need to light up those LEDs in that black box.

[keeney123]

Re: how to test lcd led backlight?

When I was a kid my Dad would take the tubes out of the TV and bring them down to the hardware store and plug them into the standardized tester to find out which tube was bad. Once he found out, the hardware store had the replacements and he would buy it and our family could watch TV for another 6 months to a year before he would have to do this again. Of course most tubes would fail because of the cathode heater. Yes there were switches and a look up chart.

[JeffJ]

Re: how to test lcd led backlight?

Vf is the kicker here. this is exactly why most of the led controllers shut down or drop off voltage because vf is incorrect, be it open or dead short. with out knowing the exact design of each individual circuit. connecting a random box that applies voltage and amperage will smoke something. If we had this info we shouldn't need a tester because we would have schematics. so...

There is a reason why manufacturers consider these non replaceable parts, because diagnostics are tiedeous and the cost to do so is less then them replacing the unit for warranty. I can tell you this. if you have a tv with bad LED clusters under warranty. You get a refurb and they scrap your sent in unit except the boards possibly.

[budm]

Re: how to test lcd led backlight?

".EX: Samsung LED 55' TV , the LEDs are 7983340.... 33 means 3.3v 40 ..means 40ma and we know from 2015-2018 they use this kind of LEDs /by total current ....we will know exactly how many they used" I sure like to know where he gets this info from.