RCA LED55G55R120Q LED Current Adjustment

[Hy4woj]

Hey Guys,

I wanted to see if anyone has any experience adjusting the LED current on the LED55G55R120Q model. I have one that I got for free that had blown LED backlights. Instead of just replacing the LEDs I would like to lower the current to lengthen the life of the LEDs. I was told this unit's LED driver doesn't have a control IC

[budm]

Re: RCA LED55G55R120Q LED Current Adjustment

Lets see good clear pictures of the boards, especially the power supply board top and bottom side.
There are more thna one version of this model:
http://www.shopjimmy.com/catalogsear...+LED55G55R120Q

[Hy4woj]

Re: RCA LED55G55R120Q LED Current Adjustment

I have attached pictures of the power board LED output area.

[Hy4woj]

Re: RCA LED55G55R120Q LED Current Adjustment

It doesn't appear to have an LED controller, just diodes, caps and what appears to be a current limiting resistor!

[budm]

Re: RCA LED55G55R120Q LED Current Adjustment

What is the P/N of that 14-pin SMD IC U301?
That should be the LED control IC, you can see the ADJ (DIM/Backlights level) pin 2 of CON 4 goes to that IC.

[budm]

Re: RCA LED55G55R120Q LED Current Adjustment

BTW, can you take good focused straight shot pictures of the whole top and bottom side of the board? I have hard time tracing out the connections.

[Hy4woj]

Re: RCA LED55G55R120Q LED Current Adjustment

What is the P/N of that 14-pin SMD IC U301?
That should be the LED control IC, you can see the ADJ (DIM/Backlights level) pin 2 of CON 4 goes to that IC.

U301 is an LM324

[budm]

Re: RCA LED55G55R120Q LED Current Adjustment

How about U302 on the top side?

[Hy4woj]

Re: RCA LED55G55R120Q LED Current Adjustment

I replaced the circled resistor that was 1 ohm with a 1.5 ohm resistor. This dropped the LED current from 320ma to 220ma!

[budm]

Re: RCA LED55G55R120Q LED Current Adjustment

OK, that must be the LED current sensing resistor, the V drops on that resistor is used for feedback to maintain constant set LED current. It was hard to trace the circuit using your pictures. 220mA should be more than low enough to extend the life of the LEDs.