is it possible for every LED in a backlight assembly to fail?

[rockit711]

I'm trying to fix up a Palsonic 50" LED TV, I suspected a LED failure as all the symptoms were there (power comes up fine, image displayed but no back light, LED power comes up initially then shuts off quickly triggering the driver chips fault pin etc.)

Once I got the screen off there were obviously two failed LEDs straight up (clearly burnt out, black soot around them and melted plastic caps). but the rest look OK. However once I started testing them it appears that every single one has failed! the Diode test on the DMM didn't illuminate a single one, even slightly. The 2xAA test likewise failed to illuminate any that I've tested (about 50% of them so far).

Before going any further was just wondering if anyone has ever come across a set that has had every single LED fail? It seems unlikely to me - surely one would go open circuit before they ALL failed!

Or much more likely is there something I may be missing?

[budm]

Re: is it possible for every LED in a backlight assembly to fail?

Does the LED show about 0.7V IN DIODE MODE test when it is tested in Reverse bias.
Are the LED rated at 3V or 6V (Dual-LED in one body).
You must be careful when testing the LED without current limiter if you connect the power source to the LED in the reverse bias, that built-in protection diode will heavily conduct and get damaged. The protection diode is connected in anti-parallel with the LED.
I will never test the LED without using the power supply with current limiter function otherwise you can easily damage the good LED.
http://led.linear1.org/why-do-i-need...r-with-an-led/
Pictures of the LEDs, LED assembly?
BTW, what is the maximum Voltage and Current the meter can put out in Diode mode test? It should be in the spec sheet of the meter.
BTW, if you want to know how much current will flow through diode in forward bias mode that is connected to 3V power source without current limiter, do the experiment and try it out by using DCA meter in series with your 3V batteries pack and the diode.

[rockit711]

Re: is it possible for every LED in a backlight assembly to fail?

Are the LED rated at 3V or 6V (Dual-LED in one body).

That did it, they were 6V! I didn't know about those.