RCA RLED6090 backlight goes affter 10 minutes

[Anooc7]

Hi,
I have this rled 6090 led tv which has this backlight issue, When I change it to energy saving mode and tv works fine , All the other mods has this issue. I have entered the service menu by pressing input + 2580 and reduced the backlight to 50% . But as soon as I exit from that service menu it goes back to higher levels. (Since there is no options to save it) . There is a small ic near led drive section a dual opamp , as358m . Is it serves as a controller for backlight? How do I reduce the backlight level using an increased current sense resistance or something like that? The psb is ER991D
Checked both the led strip end and both works with same 170v .
Thanks in advance

[CityZen]

LED brightness is typically adjusted by PWM (pulse width modulation).

[neilc6]

I don't touch RCAs any more. You can't find new strips for these which is the correct repair. Strips could still fail in the future even with the backlight level lowered.

[Anooc7]

Originally Posted by CityZen

LED brightness is typically adjusted by PWM (pulse width modulation).

I couldn’t find the schematic, very unfortunate on that.

[Anooc7]

Originally Posted by neilc6

I don't touch RCAs any more. You can't find new strips for these which is the correct repair. Strips could still fail in the future even with the backlight level lowered.

Yeah , so true. Since every strips works I wouldn’t be able to find the faulty one too unless I have a single oem strip to replace, and its a headache.

[CityZen]

If nothing else, you could add some diodes inline with the LED outputs. Each will drop the voltage a bit and thus dim the LEDs correspondingly.

[lotas]

Originally Posted by CityZen

If nothing else, you could add some diodes inline with the LED outputs. Each will drop the voltage a bit and thus dim the LEDs correspondingly.

It is not necessary to reduce the voltage, but the current that is supplied to the LEDs.

What is (name) LED driver U303 worth?

[alfatv]

You have 2 possibilities here:
1. Proper repair
2. Band aid

For #1 you need a good LED tester with high current. Check each strip separately, the bad one should have at least higher voltage drop or maybe even go open. Then with this method you can find that single LED.

For #2 you can just use eco mode. If you reduce current, the effect will be almost the same.
If you really want to lower the current, I think R5501 is current sensing resistor.
Just don't do it for customer especially if you charge money.

[Anooc7]

Originally Posted by alfatv

You have 2 possibilities here:
1. Proper repair
2. Band aid

For #1 you need a good LED tester with high current. Check each strip separately, the bad one should have at least higher voltage drop or maybe even go open. Then with this method you can find that single LED.

For #2 you can just use eco mode. If you reduce current, the effect will be almost the same.
If you really want to lower the current, I think R5501 is current sensing resistor.
Just don't do it for customer especially if you charge money.

Thank you so much, I will try to modify the current sensing resistor. So do I need to increase its value? (It is a 0.8 Ohm resistor so how much do I need to change its value? )The customer is happy to repair it cheap but he need a bit more brightness than eco.
Thanks

[alfatv]

As I said, don't do it, just return and don't charge anything.

[Anooc7]

For those who have similar issues here is the fix, I have added 3x 0.6 ohm 2 watt resistors (I didn’t have any 2ohm single ones) in series with R5501 and It works great. Your human eye will never notice any difference at all , and its brightness setting is still in the middle and sufficient for my happy client . I did increase the brightness to 80% and it still worked without any issues.