Samsung UA32D4003BM 32" LED NO POWER

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

Vcc for the LM358 can come from a 9V battery or other power source minimum 6V maximum 30V.
You can use 2N60B.
V+ is the 210V.
The one LED would be replaced by the whole strip.
The circuit ground connects to the TV's chassis ground so the current can return.

[Alastair E]

Re: Samsung UA32D4003BM 32" LED NO POWER

Easiest way Ive checked LED strips is to use Two 15W 240V lamps connected series then connect Those in series with the LED strip and connect to 240V AC....

The Lamps Limit the current to around 40mA and the LED should light if they are OK....

Much simpler circuit than the earlier one mentioned.

Dont however, run the LED string like this for too long......

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

Doing that will expose the LED strip to high PIV (peak inverse) from the mains negative cycle plus who-knows-what kinds of transients. They are delicate semiconductors, not things like bulbs which can withstand these transients. It sounds risky, to me.

[Alastair E]

Re: Samsung UA32D4003BM 32" LED NO POWER

Aye--But wasnt recommending they should be run for long like that--Just long enough to confirm they work!

PIV for a LED--what, even if only 10V (They are somewhat higher...) would exceed anything they would 'see' connected this way...
Could always add a diode in series if you were concerned about the PIV....

As to transients--LED's can stand huge transients for very small timescales--Thats how they use 'em as flash-bulbs!

Heat is what kills 'em.....

Somewhere, Ive got a strip I rescued--IF I can find it, I'll wire up like this--See how long it lasts!

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

LEDs are current driven, not voltage driven.
If you had an active ballast limiting to 40mA I would say its OK, but your current is going to vary with the panel size so it's risking potential damage. (especially if there is an internal short.)
I haven't done much with LED TVs, so maybe I'll use this trick one day, but for now, call me a coward :P.

[Alastair E]

Re: Samsung UA32D4003BM 32" LED NO POWER

Nah--Not Coward--Cautious!

NOTHING wrong with That!

Me, I'm an old codger--If it blows--It needed replacing anyway!

[stj]

Re: Samsung UA32D4003BM 32" LED NO POWER

just so you know,
you cant reliably meter the current or anything with a mutimeter.

most led drivers use high frequency pwm drive to control the brightness - the output is not dc.
there are a few crapy exceptions, but the modern ones are all strobed - it keeps the percieved brightness up while reducing heat & power consumption to extend the life of the led's

you can see it by poking the led outputs with a scope.
not a tool i'v ever heard mentioned on his site btw, even though i'v got 3 myself!

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

It can work; a good DMM will read an average. A bad DMM will not, though. A scope is best, I use Rigol DS1074Z.
PWM and high current is a myth: it actually reduces perceived light intensity. The reason for doing it is because the lights can be dimmed.

[stj]

Re: Samsung UA32D4003BM 32" LED NO POWER

if you have one current-source and several strings of leds,
by quickly switching the source across the strings you light them all while minimising the psu current - that's how the ones i'v got work.
like time-division multiplexing.
unfortunatly it makes the driver chips more likely to fail!

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

just to makesure one more time, before i put everything together.

do i have a go to plug it in?

[stj]

Re: Samsung UA32D4003BM 32" LED NO POWER

that's not a bad design,
but you could use an L200 current regulator.
http://datasheetcatalog.com/datashee...0/0/L200.shtml

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

What you can do for now is use a12v PSU and they loading that down first. That way you aren't working with high voltage immediately.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

i've tried the above diagram but got no change,

any more ideas before i try to order a new psu board?

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

This is to show what you can do with your meter, you can use cheap TENMA meter or hundreds of dollar meter (FLUKE 187) to check LED backlights voltages and current of the TV.
Frequency of the output is 90KHz. I have done many and enough for verification of open LED strings. The DC is average reading but at least it shows you do have voltage and current if the string is not open.
This is SAMSUNG

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

what should i measure?
i have "MY-64" multimeter

i already tested for voltages and current>

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

i've tried the above diagram but got no change,

any more ideas before i try to order a new psu board?

What do you mean? You do not see the LED light up? How did you power that OPAMP? Try scaling down the voltage so you you can use 12V lamp to see if the circuit that you built is actually working.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

yes the led will not light up,
the tv keeps blinking.
i powered the OPAMP with external 12v 1a adaptor.

(maybe i wired it wrong?)

could you have a look at the diagram i have updated?

where goes the (-) from the extrenal adator?

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

Eventually i bought a used power board from shopjimmy for 80$

The TV is now back to life !!!

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

Thanks for the repair feedback.

[fredaelsadany]

Re: Samsung UA32D4003BM 32" LED NO POWER

Hallo all
I think this circuit help you .
the inverter not working it is suppllied with 145v and raised it to 195v by buck inverter .
i solved this samsung there is bad mosfet QQ854 . THE ON/OFF CIR IS BAD AND THIS CIR IS APPLIED TO MORE THAN ONE SAMSUNG TYPE .
THANKS