LG 50UH500 LED Current Mod help needed

[budm]

Re: LG 50UH500 LED Current Mod help needed

Removed (R419, 420, 423) and the current dropped nicely from 350 MA to 210. A fairly significant drop, but these TV's fail when 1 year old so they must have been seriously overdriven.

They made them to fail just about after the warranty runs out.
Thanks for the follow-up.

[budm]

Re: LG 50UH500 LED Current Mod help needed

BTW, are the pictures still bright enough for daytime watching after the mod?

[jjanssen7]

Re: LG 50UH500 LED Current Mod help needed

I had a very hard time telling the difference, at first I thought the mod didn't work but once I actually tested the current it showed how much change there was. This TV and the 65UH5500 are both terribly common LED failures from what I've seen. I'm going to tackle the 65" version next, but I can already see what needs to be modified.

[alfatv]

Re: LG 50UH500 LED Current Mod help needed

Was looking to do the same, then came across this thread which confirmed my thinking.
Done this mod, it works like normal TV now and not like piece of sunshine.
Thank you all!

[budm]

Re: LG 50UH500 LED Current Mod help needed

Was looking to do the same, then came across this thread which confirmed my thinking.
Done this mod, it works like normal TV now and not like piece of sunshine.
Thank you all!

Thanks for the info, glad that it works for you too.

[Diah]

Re: LG 50UH500 LED Current Mod help needed

any one take a look at R you are removing at other powerboards for different screen size such series 5500 8500- even this threat 500. HDR function need this currents.. other wise the picture will look yellowish. if you are so worry on yours LED didn't failed then keep the currents as it and reduce BL setting to low.

this trying mode can be applied only for LED TV HD / HD ready, and only for people whose eyes didn't remark differences LOL

[alfatv]

Re: LG 50UH500 LED Current Mod help needed

any one take a look at R you are removing at other powerboards for different screen size such series 5500 8500- even this threat 500. HDR function need this currents.. other wise the picture will look yellowish. if you are so worry on yours LED didn't failed then keep the currents as it and reduce BL setting to low.

this trying mode can be applied only for LED TV HD / HD ready, and only for people whose eyes didn't remark differences LOL

I assume that lowering current via sense resistor is the same as lowering backlight setting in the menu.
HDR in that TV has it's own backlight setting 0-100.
If I am wrong, please explain.

[Diah]

Re: LG 50UH500 LED Current Mod help needed

I assume that lowering current via sense resistor is the same as lowering backlight setting in the menu.
HDR in that TV has it's own backlight setting 0-100.
If I am wrong, please explain.

the answer you can find it self by measuring the BL currents in mA at any step of BL level & HDR level too.
yes HDR most brands make the factory setting of BL 100. but this adjustable. and the 100 level doesn't mean the maximum high level of LEDs unit capacities

[alfatv]

Re: LG 50UH500 LED Current Mod help needed

OK, i started reading about HDR, it does require more brightness which should come from more backlight.
At the same time these UH series are using tiny 3030 LEDs on normal FR4 PCB substrate.
Obviously LEDs are overdriven and overheated, then fail soon.
On top of that, LG didn't bother to reduce backlight for normal content which could help to mitigate this problem.
On Amazon Prime you can't even turn HDR off

So, welcome to our new enemy:

HDR



But it will keep repair shops busy, hahaha

[nomoresonys]

Re: LG 50UH500 LED Current Mod help needed

With the prices of tvs today it will keep the landfills full.

[budm]

Re: LG 50UH500 LED Current Mod help needed

https://www.badcaps.net/forum/showpo...&postcount=433
All the TV's, even with HDR I use in my video lab have LED modification which is done with the help of the TV OEM. in the lab we have equipment to verify that the all the TV function, I.E. HDR is still performing per spec (we have Hokey puck sensor module attach to the screen and video generator with HDR for verification, not by eyes). So it s not issue with hardware modification to limit the maximum LED current, in fact OEM do know about the issue. We work with many TV OEM since the products we make have to be compatible with so many TV out there.
BTW, if you manually set the backlights level to I.E. 80%, the MAX LED level will still be at 80% not 100% even with HDR, just think about it, you you watch TV in darken room so you set the backlights to 80% since you do not need that much backlights like day time watching, if the HDR force backlights to be at 100% then the image will not look correct when backlghts is set to low level, the HDR will adjust according to TV setting. Nothing complicate about that.
When you work closely with OEM to develop products and also provide feedback to the OEM, you get info that is not available to public or even authorized service center.
BTW, since the constant current for maintaining the current through the LED is done with PWM, it means the current though the LED is still at the max current set by the sensing resistor, but the on time of the LED is based on the Pulse width of the PWM, I.E, max set current is 1A but you set the PWM to 50%, the the average current is 0.50A. Most backlights circuit use PWM between 10% ~ 90% to represent 0 ~ 100 (some OEM may use 0 ~ 50 scale) scale on the User OSD.

[nomoresonys]

Re: LG 50UH500 LED Current Mod help needed

Quote: "BTW, since the constant current for maintaining the current through the LED is done with PWM, it means the current though the LED is still at the max current set by the sensing resistor, but the on time of the LED is based on the Pulse width of the PWM, I.E, max set current is 1A but you set the PWM to 50%, the the average current is 0.50A. Most backlights circuit use PWM between 10% ~ 90% to represent 0 ~ 100 (some OEM may use 0 ~ 50 scale) scale on the User OSD"

So to simplify Bud, does this mean that a resistor modification is the best way to get the current to an acceptable level that won't prematurely burn out the backlights?

[Diah]

Re: LG 50UH500 LED Current Mod help needed

the subject become interesting.. good all of us can now agree on Pulse width roll at this subject. Pulse width are Firmware script Steps, usually this script started to control the LEDs currents with first startup steps. ( we can notice the Logo come out bright then the screen dimming.) the important things at this script it can sending test (TX) and receive answer (RX) not only about the healthy condition of BL but also LVDS/T-CON/Sound/Tuner etc. any answer failed it will turn self to shutdown or ERROR blinking code this depend of the type of the script if engineer included this function at it.

we do know this Pulse width will turn on PWM to it 100. but its currents always under the LED Units capacities, removing ONE of the sensing Resistor indeed it will decrease the 100 start. but we will let MOSFET and the U1 IC under less protection if one of the LEDs shorted. ( So why they put 3 R .. they can put 1 or 2 to reach the same value of all 3 together in parallel !

Software designer considered this, and gave to users / factories the abilities to decrease the 100 start ( see attached photo the eeprom of BL steps setting ). beside this they used circuit at HW level to let the 100 Start always are 90% or less of the LED capacities. ( unfortunately not all of course ).

[budm]

Re: LG 50UH500 LED Current Mod help needed

1) Why using resistors in parallel? Never seen that being used? You parallel sensing resistors to get the correct value based on the calculated current requirement which may mean that the standard value resistor will not work, paralleling resistors to get the require value is common practice, I.E. your calculation calls for 1.10 Ohms resistor so you can use 2.20 Ohms in parallel to meet your requirement.. Using resistors in parallel also allow you do use smaller body resistor to distributing the power dissipation.

2) LED driver has local protection against no load condition, over current condition so it does not need the control from main board, I.E. Self test function of the power supply board that has pull-up resistors when you disconnect the power supply board from main board, the PWM will be at 100%. The error signal form LED driver can be sent to the main board to be used to MCU to do more circuit down if desired, most low coast TV do not utilize the error signal form the LED driver circuit.

[budm]

Re: LG 50UH500 LED Current Mod help needed

Quote: "BTW, since the constant current for maintaining the current through the LED is done with PWM, it means the current though the LED is still at the max current set by the sensing resistor, but the on time of the LED is based on the Pulse width of the PWM, I.E, max set current is 1A but you set the PWM to 50%, the the average current is 0.50A. Most backlights circuit use PWM between 10% ~ 90% to represent 0 ~ 100 (some OEM may use 0 ~ 50 scale) scale on the User OSD"

So to simplify Bud, does this mean that a resistor modification is the best way to get the current to an acceptable level that won't prematurely burn out the backlights?

The TV's in the lab are running 24/7 so we do not have to calibrate them everyday and the lab is kept at constant temperature, you can easily reduce the backlights level by 20% and your eyes will have a hard time telling the difference.

[Pitoniak]

Re: LG 50UH500 LED Current Mod help needed

Was looking to do the same, then came across this thread which confirmed my thinking.
Done this mod, it works like normal TV now and not like piece of sunshine.
Thank you all!

So was this resistor mod done on a lg65uh5500?
What resistors on the led driver board where removed?
All the threads on this referred to the lg50.
Need to know if I can do this mod to my lg65uh5500 tv.

[jjanssen7]

Re: LG 50UH500 LED Current Mod help needed

Yes, in my experience the equivalent mod has to be done on the 65" version of this tvs or it will just burn out the new set of (replacement) Leds.

I remove R425,R424,R421, R419, R417, and R415 (or remove one out of the 3 parallel resistors per array). That brought the current down to a more long lasting level.

[Pitoniak]

Re: LG 50UH500 LED Current Mod help needed

I have the 65uh5500 . I will do the mod on led board by removal the resistors as indicated.
But I have a question regarding this mod. First of all by removing the fail safe wire and turning on this tv it operates perfectly. Reinstalling this wire and it shuts down. The voltage is 90v the led board it should be 80volts. Will mod fix the shut down with the fail safe wire connected? Also what if I use the tv without the fail safe wire installed on? It seems as though the fail wire is installed for led failure or maybe over voltage. I am just guessing. What are your thoughts?

[jjanssen7]

Re: LG 50UH500 LED Current Mod help needed

What fail wire are you speaking of? This mod will only work if all the backlights are functional.