LED backlight tester circuit

[2many]

From what I've read, LED backlights on TV's run between 90V to 120 vdc. I know my power supply is bad but want to build a LED tester to see if my LED's are good. If they are bad, I will stop any further work in trying to fix the TV since replacement LED strips are not available for this set, which limits me to replacing individual LED's, which I do not have the tools for at the moment.

Anyone built their own LED test power supply?
For a crude LED tester, I was thinking of using 120 v ac line voltage, a half wave rectifier, a 500 uf filter cap and a current limiting resistor. The half wave is so I don't exceed the 120 vdc, but will give more ripples. Full wave will have less ripples, but the voltage may end up at around 150 vdc. LED's are current driven devices. Maybe a full wave should be fine as long as my current limiting resistor is the correct value and not exceed the current rating of the LED's.

How do I find the total LED current rating of my set? It's a 50" Toshiba 50L2300U. What is the approx. current to the LED's of a a 50" TV?

[6ot4hr]

Re: LED backlight tester circuit

You can test your LED backlight led's using a digital multimeter, just put it to Diode testing mode and probe each of the led's, they should give a little shine if you get the polarity right. Also multimeter will beep or show 0ohm resistance if you find one shorted, or give OL / open circuit if that LED is dead.
That's how i do it.
Best solution to test the LED backlight is to turn the TV on with led backlight connected, you will automatically see which one of the LED is dead, preasuming power supply is okay.

[2many]

Re: LED backlight tester circuit

But getting to the LED strips is a big job, which I am not ready to do, that's why I want to power them up with a test power supply. A multi-meter on the diode test mode can only test individual LED's, not when a bunch of them are in series as wired in a TV. I'm not sure if you can get a reading on a bunch of LED's in series even with the multi meter in the meg ohm scale.

[gabiz_ro]

Re: LED backlight tester circuit

In some cases depend on what multimeter you use.
Some of them doesn't have over 3V on diode test.
As result no chance to identify one bad led.
Some of them still have over 3V voltage on diode test,so you can see a little light from led on test.
But in case led inside is in fact two or three of them in same package,no chance to identify one bad led.

[Moreno83]

Re: LED backlight tester circuit

You can't repair the power supply of the tv? Whats the model number of the power supply?

[2many]

Re: LED backlight tester circuit

You can't repair the power supply of the tv? Whats the model number of the power supply?

I am trying to fix the PS. See this thread https://www.badcaps.net/forum/showthread.php?t=55987

power supply board number is there.

[budm]

Re: LED backlight tester circuit

http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm

[johns1mj]

Re: LED backlight tester circuit

I just tried using a model train power supply to check led strips. My dc power supply has a max output of 17.6 volts. I can test up to 5 in a strip. 10 is to many for my power supply to power up. Has any one else found something like this to use?

[ozzy214]

Re: LED backlight tester circuit

http://www.ebay.com/itm/221835891794...%3AMEBIDX%3AIT

Adjust to voltage needed for input and output. I currently use it for leds I made into nightlights for my sexy time bedroom...red light district wink wink!!

I took tv leds and spray painted blood red, works awsome......

[budm]

Re: LED backlight tester circuit

I just tried using a model train power supply to check led strips. My dc power supply has a max output of 17.6 volts. I can test up to 5 in a strip. 10 is to many for my power supply to power up. Has any one else found something like this to use?

You have to be real careful testing the LED strip without current limiter or constant current.
So have 5 LEDs on the strip and you apply 17.6V directly without any current limitter, and if one of the LED shorted out, then the current flowing through the string will be so high that can damage the good LEDs. I use power supply that I can adjust the current.
If you do not have one, you can use LM317 with heat sink as constant current source for driving LED.
You can easily do the experiment and measure DCA through your LED string with your 17.6V power supply, then short out one of the LED to see what happen to the current and then look at the spec of the LED for the current handling..
LED is not linear device.
I do not understand why people keep trying to run the LEDs without any current limiting in place.

http://led.linear1.org/why-do-i-need...r-with-an-led/

[frank71x]

Re: LED backlight tester circuit

[faroek]

Re: LED backlight tester circuit

You can test your LED backlight led's using a digital multimeter, just put it to Diode testing mode and probe each of the led's, they should give a little shine if you get the polarity right. Also multimeter will beep or show 0ohm resistance if you find one shorted, or give OL / open circuit if that LED is dead.
That's how i do it.
Best solution to test the LED backlight is to turn the TV on with led backlight connected, you will automatically see which one of the LED is dead, preasuming power supply is okay.

u can only see which strip is bad, not the bad led