attempt to clone LED TV Backlight Tester

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

That's right.

On my attempt to build one,testing one single LED,input voltage was drop to 140V (due to my setup) LR8K4 was configured for 10mA and mounted on little heat sink.
After few minutes 5-10 heat sink was a little warmer than my fingers.

As for voltage drop that I said previous,I try to keep it safe,isolated from mains.
So I use two little (too little) transformers until I found one little enough 1:1
Their specs was 230V 60mA input 6V 400mA output
But was not enough,voltage dropping too much.

[budm]

Re: attempt to clone LED TV Backlight Tester

The more LEDs in series the less power dissipation for the LR8K because you will have less Vdrops on the IC, it is worst when you test 1 LED.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

I took some photos of its PCB. Although it was purchased by someone else, I think the price is reasonable.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The photo in post 38 is different. The one I have has more parts.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

You're right.....My bad, Constant current means all LEDs in series at 30ma.

"Also I don't see isolation transformer or 1:1." This I just guess because I did not have this LED tester.

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

" ......to about 30ma. " Current is too high for LEDs long time testing. 110 LEDs x 30ma = 3.300ma = 3.3A

That's wrong
Current is 30mA no matters LED's number.
110 Led's -> 330V
330V x 0.03A (same 30mA as people say previous) = 9.9W
Almost 10W,I think is a little too much for simple or single LR8K

Also I don't see isolation transformer or 1:1.
Could be live connected.
Also for 110V line could be using some voltage doubler.

That little transformer could be some part of SMPS that deliver power to microcontroller and 330V at 30mA or only for microcontroller and LED's voltage is from main line.

More clear and detailed photos can be usefull to solve the mistery.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

"There appears to be a MOSFET in series with the output that does the fast current control. " My guess, it is the LR8 (HV version of LM317)?

" a large drum inductor which must be part of a Buck regulator on the isolated side also." My guess, That is for smooth the output voltage?

"The current ramps up in steps so must be controlled by the same micro-controller that does the voltage meter function." My guess, U6 only uses for voltage meter? The current ramps up using capacitor.

PS: Why they use Epoxy because they don't want you to know it is so easy to built.

The poormans LED tester current is at 6.8ma, with no ramps up current I can calculate LEDs characteristics. Pic2.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The TV had 2 series groups of 40 LEDs each. The tester developed about 150v for the 40 series LEDs.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The interesting areas of the PCB are covered with a very tough black epoxy. There appears to be a MOSFET in series with the output that does the fast current control. There is a large drum inductor which must be part of a Buck regulator on the isolated side also.
The current ramps up in steps so must be controlled by the same micro-controller that does the voltage meter function.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Thanks for your testing results.

330v dc / 1.414= 233.38v AC. So SID GJ2C use a 1 : 1 isolation transformer but over 110v AC region they use 1 : 2 isolation transformer or ac doubler. SID GJ2C testing voltage is DC 330v / 3v LED = It can test 110 LEDs

" ......to about 30ma. " Current is too high for LEDs long time testing. 110 LEDs x 30ma = 3.300ma = 3.3A

"..........then it ramps exponentially for 2 to 3 seconds" In pic1 We can change C2 to 10uf - 100uf capacitor, give the circuit 2 - 3 seconds to charge to 1.2v for it to reach the current limited. ( I constant = 1.2v / R).

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

I did some tests on a GJ2C loaded with resistors from 470 ohms to 10K. The open circuit voltage is about 330v. When I connect a resistor, there is a brief spike of about 5ma then it settles briefly to 1ma then it ramps exponentially for 2 to 3 seconds to about 30ma.
The built in voltage meter is accurate.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

I wish the best for you

[capwizard]

Re: attempt to clone LED TV Backlight Tester

You're more than welcome.
Eres más que bienvenido.

We are a bunch of electronic hobbyists to help each other like A big family.
And our mission is to Recycle the World.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

"I need the schematic for backlight tester Gj2c"

Although SID GJ2C is made in China, it may has copyright, but we teach you how to catch fish. you don't need the schematic, because you can make A better one, like battery powered Oled display LED tester or use microcontroller shows how many LEDs and protection diodes inside the screen and panel's suppose working voltage and current, would that be nice?

If you find this forum helpful? You might consider to donate here.

At the very bottom of this https://www.badcaps.net/forum/index.php page, Push the Orange button.

thank you very much

[capwizard]

Re: attempt to clone LED TV Backlight Tester

"I need the schematic for backlight tester Gj2c"

Although SID GJ2C is made in China, it may has copyright, but we teach you how to catch fish. you don't need the schematic, because you can make A better one, like battery powered Oled display LED tester or use microcontroller shows how many LEDs and protection diodes inside the screen and panel's suppose working voltage and current, would that be nice?

If you find this forum helpful? You might consider to donate here.

At the very bottom of this https://www.badcaps.net/forum/index.php page, Push the Orange button.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Mi amigo, está aquí..............Probador LED cuesta sólo $ 5. El probador es inseguro pero barato, por favor no lo use en armas nucleares.

https://www.badcaps.net/forum/showthread.php?t=59136

If you find this forum helpful? You might consider to donate here.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

Hello
I need the schematic backlight tester Gj2c
thanks
http://www.ebay.com/p/Sid-Gj2c-LED-T...ter/1373031177

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Nice,it could supply up to 60V DC. But To test edge led tv strips ( 4 of them for 60" ) each needs 186v dc, then you will need that plus 10x 9v battery to test.

[llonen]

Re: attempt to clone LED TV Backlight Tester

Nice looking power supply, not one I would choose to testing back lights though,

I think I paid around £5.00 for one of these which I use for various applications including testing back-light strips.

https://wiki.london.hackspace.org.uk...0_Power_Supply

[capwizard]

Re: attempt to clone LED TV Backlight Tester

llonen: using a variable precision bench power supply with adjustable current limiting.
B&K Precision 9803 The output can be varied from 0 to 300 V with 0.1 V programming resolution. $2,950.00 (Each)
http://www.alliedelec.com/b-k-precis...i9MaAsuc8P8HAQ

But our budget have only around $10. .