UN55D6000 Blinking Standby Light

[tom66]

Re: UN55D6000 Blinking Standby Light

If those bottom LEDs are short circuits, the LEDs should be just as bright (circuit will drive a constant current regardless); if they are in between, then the LEDs might be dimmer.

[mmartell]

Re: UN55D6000 Blinking Standby Light

Sort of...

As can be seen the led's on the bad strip are quite a bit less intense on the top half as the bottom half. Can that be explained by the fact the bottom has 19 of 50 led's out ?

[mmartell]

Re: UN55D6000 Blinking Standby Light

Well of course I got impatient and put a wire across the two open diodes...

SUCCESS !!

[mmartell]

Re: UN55D6000 Blinking Standby Light

Ok tom thanks for your help and patience as always. I will try to find another strip, or one to harvest good led's from anyway.

[tom66]

Re: UN55D6000 Blinking Standby Light

Yes, original problem returns with finding I.

[mmartell]

Re: UN55D6000 Blinking Standby Light

Can't you use resistor(s) to drop the voltage 165v or are we back to the unknown amperage thing ?

[tom66]

Re: UN55D6000 Blinking Standby Light

How would you halve the PSU output?

[mmartell]

Re: UN55D6000 Blinking Standby Light

So I guess you don't suggest using a resistor based on say 80% of rated current capacity ?

Or what if I wanted to halve the PS output so I could use the one known good string, would the value be 165v/.28A and then V^2/R for the wattage or is that not advisable, too ?

[tom66]

Re: UN55D6000 Blinking Standby Light

Oh... my error then. I don't know what you can do, unfortunately .

[mmartell]

Re: UN55D6000 Blinking Standby Light

With my DMM as you suggested

[tom66]

Re: UN55D6000 Blinking Standby Light

So, how did you get the LEDs to light up? Did you test them individually?

[mmartell]

Re: UN55D6000 Blinking Standby Light

Power supply won't even fire up with the backlights the way they are. In fact I originally thought I needed a main board, then thought, no the power supply is fubar then realized the backlights were possibly the problem the whole time. I think confirmed by the shorted led's.

So in fact this is the first kink in the chain that needs ironing out before I can say any of the other boards are good or not.

[tom66]

Re: UN55D6000 Blinking Standby Light

Can't you measure it through the working one?

[mmartell]

Re: UN55D6000 Blinking Standby Light

But this is chicken and egg I can't measure the current flowing through the string without the string working. Is it advisable to use the design maximum or like 80% of it to make the calculation ?

[tom66]

Re: UN55D6000 Blinking Standby Light

Probably a design maximum.

[mmartell]

Re: UN55D6000 Blinking Standby Light

The board says 330v/280mA for that circuit is that not what we need ?

[tom66]

Re: UN55D6000 Blinking Standby Light

You need to know the current through the LEDs to calculate the resistance which produces a desired voltage drop.

e.g. you need to drop 165V when 0.1 amps flows, R=1650 ohms (V=IR, I=V/R, R=V/I) and power dissipated would be VI or V^2/R or in this instance about 17 watts. So choose a 25 watt wirewound resistor.

However, you do not know how much current each LED string draws; you need to measure that before calculating R.

[mmartell]

Re: UN55D6000 Blinking Standby Light

If everything works out I intend to replace them. However my electronics math/theory is still in its infancy so I need my hand held figuring that resistor value.

Before you said the strings were in parallel I figured a 120ohm 8 watt resistor (!) but even if that WAS right for a series string wouldn't it be different in light of the fact they are not wired that way ?

[tom66]

Re: UN55D6000 Blinking Standby Light

approximately 20 white LEDs They are non linear so can only roughly be approximated with a resistor.

[mmartell]

Re: UN55D6000 Blinking Standby Light

What's the easiest way to present a dummy load based on the fact 20 led's are out so I can test the power supply and the remaining led's ?