lg 60uj6300 dim backlights

[shadetreetrader11]

Have a lg 60uj6300 that has a very dim backlight. I have tried shutting all the eco settings off and no change. If I use my led backlight tester it lights the backlights nicely.(I'm not able to see if they are all lit but definitely much brighter) This tv has 2 wires from power supply to backlights. The black wire has 260v and the white wire is measuring 15.1v. Any ideas?

ms 2.07
pdim .265
pwr-on 3.3
the remaining pins are all labeled 13.2 and they all measure 13.1

[lotas]

Who measures the voltage at the backlight output like this, you need to measure between the white and black wires.

And PDIM - .265v (backlight brightness level) is low...

[Davi.p]

try jumpering Ms-Pdim..

[shadetreetrader11]

Lotas my bad. Remeasured across black and white and I get 247v. I jumped Ms-pdim and it actually dropped the voltage of the backlights to roughly 90v.

[Davi.p]

247v is too high , you are maybe reading a pulsanting voltage due to bad final el.co.

[shadetreetrader11]

When I put my led tester across the leads that feed the backlights it goes full bright at 168v and 90 mil amps. And when I plug the connector back to the tv power supply that is putting out 247v it's extremely dim. Why so dim? If my voltage is at 247v wouldn't it be drawing some current to fully light the leds? I'm confused

[shadetreetrader11]

Picture of scope reading across the two wires from psb to leds

[Davi.p]

Oh well, this lets me think of bad leds.. 90mA is quite low and it is not surely full brightness

[zomi]

Is there any blue purple tint to the lcd ?

[shadetreetrader11]

Zomi. Yes there is a blue/purple tint sorta half lit

[Davi.p]

this is a further clue of bad leds..

[zomi]

Change the leds, they are gone.
All lg's blue tint change ---> leds.

[Davi.p]

I think it's strange too the so high voltage, one booster is regulated for a certain maximum, that max is printed on the pcb table, so i would check those 4 diodes in top left corner, it seems a graetz bridge that gets current from transformer, if one diode is open, the thing works at half sinewave and the booster fails to work...

[shadetreetrader11]

Took it apart and leds look fine.

[shadetreetrader11]

I also checked the diodes and they were good.

[Diah]

Took it apart and leds look fine.

how they look fine ?? from your measurement listed at first post you have shorted zener diode at one or more LEDs
this LG LED are build in zener diode at reverse way to diode light... need to test one by one in diode mode... and the reading of zener should be no less than 0.65 pulling current

shorted zener or open will pass by LED tester... and will never discover them

[shadetreetrader11]

Lotas posted that .265v on pdim was to low. Is this .265 coming from the mother board?

[Diah]

Lotas posted that .265v on pdim was to low. Is this .265 coming from the mother board?

no one mentioned over here the Nature of the LED unit build in this Set...
take it apart and test yours LEDs with diode mode you will find the issue at zener diode.

[shadetreetrader11]

All diodes have point .74 v and no shorts. I also individually checked each led with meter in diode mode. One direction lit the led and the other did nothing. There is 5 rows of leds. Each row has 11 leds. 2 pieces connect together. One has 5, the other has 6 leds. I powered up the backlights again using the tvs power supply and measured the voltage across the tiny surface mount diodes mounted on the strips. The strips with 5 leds measured 12.8 v across them. The strips with 6 leds measured 15 35 across them. Everything looked correct to me. But if I'm missing something I'm all ears. Thanks

[Diah]

All diodes have point .74 v and no shorts. I also individually checked each led with meter in diode mode. One direction lit the led and the other did nothing. There is 5 rows of leds. Each row has 11 leds. 2 pieces connect together. One has 5, the other has 6 leds. I powered up the backlights again using the tvs power supply and measured the voltage across the tiny surface mount diodes mounted on the strips. The strips with 5 leds measured 12.8 v across them. The strips with 6 leds measured 15 35 across them. Everything looked correct to me. But if I'm missing something I'm all ears. Thanks

interesting what you write--- show me the strips please , the label of them and the tiny diode you mentioned