LG 70LB7100 Led Strip Replacement Question

[vinceroger69]

Re: LG 70LB7100 Led Strip Replacement Question

Saw a video of lg repair with white spots all over screen. When they took it apart almost all of the lens had fallen off.
https://www.youtube.com/watch?v=Nvwk7mpyx9Q&t=598s

Thats a good video i didnt know you could get/buy the double sided tape strips hes using to replace the led strips

[budm]

Re: LG 70LB7100 Led Strip Replacement Question

"its is strange how "basically" one big led string row with 16 leds on it- exactly one half of it dies after few minutes- side that gets power to it first??? same as if it is getting only half of power to it and only able to power on 8 leds. so power goes thru 8 non working leds and goes into working 8 leds- this rules out bad connection ??? then after first second random one on same side of screen dies in same manner-other far half continues to works, then whole screen dies, same as if power supply is weakening and losing half of power to some outputs to led rows and finally it shuts down. "
Well,, seems like you still do not understand how the connections are made and how it works.
ALL the + of the LED strips are connected together at the power supply board via LED+, the LED strip with 16 LEDs has two set of LED, each set has 8 LEDs connected in series. The Anode of each set of LED is connected to the + pin of the connector, each one of the Cathode return of each set is connected to the (-) that is why you have two (-). Sine you have two return wires for each set of the LED, and each return wire is connected to each MOSFET for controlling just one set of the two of the LED on the strip, if one of the two (-) return has open circuit then you will only see 8 of the 16 LEDs come on so that does not rule out bad connection, and it also means that the 52V on the power supply board is OK.
Another key point that I am trying to get though is that do you lose the 52vdc FEEDING ALL THE LED+ ON THE POWER SUPPLY BOARD OR NOT. If you lose the 52V on the power supply then NONE of the LEDs will ever light up, but you indicate that some strip goes off and some strips are still on then that 52V MUST BE PRESENT.
MOSFET testing, you will have to check and see there is GATE drive Voltage or not, then you need to check the Drain Voltage which I already told you to check ALL VC_1~16, it did not sound like you have done that either.
BTW when connecting device in parallel, what do you think will happen of one of the device shorted out, all the of the LED will be off also, it is just the opposite of series connection, one go open circuit ins series connection all the LEDs go, shorted LED in parallel connection all the LEDs go out, if one or more LEDs go out in parallel connection then the rest of the LEDs will get more current as shown in the learning links I provided.

[gavric]

Re: LG 70LB7100 Led Strip Replacement Question

Heat causing the glue to fail ?

its not quite really glue they used, its looking like plastic that was melted some and lens was pressed into it. i took all 128 of them off and super glued them back in place in same exact spot making sure they are centered and that three little prongs on lens get seated onto led strip , if they are not exactly centered they will shine weird glow look bad on screen, experienced it and had to re-do it.

ALL the + of the LED strips are connected together at the power supply board via LED+, the LED strip with 16 LEDs has two set of LED, each set has 8 LEDs connected in series. The Anode of each set of LED is connected to the + pin of the connector, each one of the Cathode return of each set is connected to the (-) that is why you have two (-). Sine you have two return wires for each set of the LED, and each return wire is connected to each MOSFET for controlling just one set of the two of the LED on the strip, if one of the two (-) return has open circuit then you will only see 8 of the 16 LEDs come on so that does not rule out bad connection, and it also means that the 52V on the power supply board is OK.
Another key point that I am trying to get though is that do you lose the 52vdc FEEDING ALL THE LED+ ON THE POWER SUPPLY BOARD OR NOT. If you lose the 52V on the power supply then NONE of the LEDs will ever light up, but you indicate that some strip goes off and some strips are still on then that 52V MUST BE PRESENT.

screen does black out completely after few strips die, i will take note on which strips do die and again to see if it repeats and if same strips die in same order eventually if it repeats in same order. I will be on look also to measure if i lose (-) when black out of single strip happens. if i have 2 (-) at strip connector when black out happens then it must be bad led strip or connection . i am thinking to solder up all connection between strips to make sure that is not messing me up.

[budm]

Re: LG 70LB7100 Led Strip Replacement Question

If I were you I would re-solder on those SMD connectors on those LED strips, I have seen too may intermittent or it just plain fall off the board; it will eliminate the problem in the future, every time I take the panel apart to replace LEDs I will automatically do it since I do not want to take the panel apart and take a chance on cracking the panel.

[gavric]

Re: LG 70LB7100 Led Strip Replacement Question

If I were you I would re-solder on those SMD connectors on those LED strips, I have seen too may intermittent or it just plain fall off the board; it will eliminate the problem in the future, every time I take the panel apart to replace LEDs I will automatically do it since I do not want to take the panel apart and take a chance on cracking the panel.

I resoldered all connection going into strip row, no change

When screen goes black I lose all power to it, 54VDC at +LED is gone and VC leads are dead . Few moments before "lights out" red led Led701 on power supply starts blinking 4 times, indicating some kind of error state.


I did manage to get tv to work by rewiring wires to led string rows
I "rewired" leds and tv stayed on 8+ hours now and going strong, no overheating on ps, no buzzing, no whining.

I got 3 wires to each row of leds, I got red, white and blue wires.
I connected all red wires +LED leads together. (same as factory setup)
I connected all 6 blue wires VC leads together. (now they are one)
I connected all 6 white wires VC leads together. (now they are one)

I connected red +LED to its intended power source +LED (54VDC) and either blue or white (one by one) VC leads to tv chasis for ground, backlights only flashed and 54VDC went to 0VDC. in either case did not matter white or blue wire to ground, same result

When I connected blue wires to 54VDC source (where red used to be) and white wires to ground= tv backlights work nice and long. original red wires are not connected to anywhere at all, just dangling in air.

I lost functionality of backlight lowering via tv menu and they now get constant 54VDC but it functions and tv stays on,does not seem to be extremely bright or dim.

What is bad side of me doing this except backlight control via menu (might try some old style potentiometer to lower input from 54VDC and see if i can control backlight).

[budm]

Re: LG 70LB7100 Led Strip Replacement Question

"I connected red +LED to its intended power source +LED (54VDC) and either blue or white (one by one) VC leads to tv chasis for ground, backlights only flashed and 54VDC went to 0VDC. in either case did not matter white or blue wire to ground, same result" Well, you bypass the current regulator circuit so over current sensing shut down the power supply.
"I lost functionality of backlight lowering via tv menu and they now get constant 54VDC but it functions and tv stays on,does not seem to be extremely bright or dim." The current regulation circuit is bypassed so there is nothing to control the current flowing through the LEDs.
LEDs are current device so no matter how you drive them, you need to control the current flow so it will not exceed the spec of the LED, typical spec for 1W backlights LED is around 400mA so as long as you are not exceeding it, but that is also based on ambient temperature. The current flow will also change with temperature as it heats up more then you have more current so you will have thermal run away, if the supply Voltage is not well regulated when running the LED without current regulation then the current will go up if the Voltage goes up. It is not simple as you think, that is why you have LED driver IC and the MOSFET's to control the current flowing through the LED. The resistor in series for limiting the current will have to be calculated to get the correct resistance and Wattage.
So use you dc Amp meter and check the current draw of your LEDs to see where you are at.

[gavric]

Re: LG 70LB7100 Led Strip Replacement Question

"I connected red +LED to its intended power source +LED (54VDC) and either blue or white (one by one) VC leads to tv chasis for ground, backlights only flashed and 54VDC went to 0VDC. in either case did not matter white or blue wire to ground, same result" Well, you bypass the current regulator circuit so over current sensing shut down the power supply.
"I lost functionality of backlight lowering via tv menu and they now get constant 54VDC but it functions and tv stays on,does not seem to be extremely bright or dim." The current regulation circuit is bypassed so there is nothing to control the current flowing through the LEDs.
LEDs are current device so no matter how you drive them, you need to control the current flow so it will not exceed the spec of the LED, typical spec for 1W backlights LED is around 400mA so as long as you are not exceeding it, but that is also based on ambient temperature. The current flow will also change with temperature as it heats up more then you have more current so you will have thermal run away, if the supply Voltage is not well regulated when running the LED without current regulation then the current will go up if the Voltage goes up. It is not simple as you think, that is why you have LED driver IC and the MOSFET's to control the current flowing through the LED. The resistor in series for limiting the current will have to be calculated to get the correct resistance and Wattage.
So use you dc Amp meter and check the current draw of your LEDs to see where you are at.

Thanks for this explanation.

I need to ask one question to understand something about this +Led and two VC lines on each led strip (3 wires to led strip) Is there any way to connect VC to other VC on power supply and trick power supply to think that everything is OK.

Like on some samsungs where there is only two wires going to led stip array but on power supply there is 4 outputs and two leads in the middle are connected to each other. If those wires in middle are not connected tv does not boot, bets that red blinking light.
Samsung example:
TOP1+
TOP1- --------I jumped by wire on connector to TOP2+
TOP2+ -------I jumped by wire on connector to TOP1-
TOP2-
this setup makes 4 wires into 2 wire - connected in series

Is it possible to connect my two VC lines to each other somehow and make one VC and fool main board to think that everything is good. Or connect it somehow like in samsung PS example above. Go from 3 wires to 2 wires per led string. I would like to regain control of backlight thru tv's menu and dont care about local dimming and 3d. Tv now loses all backlight if i disconnect one VC. tv thinks something is wrong.

They way i got it running now is 54VDC to one VC wire and ground to other VC and they all work. nothing going to original + on led strip and tv stays on forever.
I would like to connect it correctly to + on led strip and - on led strip (54VDC and VC output) and do something with second VC - to trick PS so i get control of backlights thru menu.

[gavric]

Re: LG 70LB7100 Led Strip Replacement Question

Current feeding all strips together is about 1.1 amp at 52VDC. I am running 9 leds on strip section and feeding 52VDC to it. All together 128 leds in this screen. Power supply is rated at 3.42Amps. Sound good?

[thelmores]

Re: LG 70LB7100 Led Strip Replacement Question

Got one of these panels donated, was trying to learn and maybe get it fixed.

Set runs 15 minutes, or couple hours..... then backlight goes out.

Anybody solve this???

[Granger]

Re: LG 70LB7100 Led Strip Replacement Question

Anyone attempting to replace the strips in their LB 70LB7100 should know that LG changed the strips (from rev 00 to rev 01) midway through production, and they are NOT interchangable. The wire connector is slightly different too.

I replaced entire rows (A,B,C sections), and have continuity between the wire leads and pins on the strips, so I think replacing a whole row will work, but I haven't tested with power yet.

Make sure you check the rev number, and make sure what you are ordering is the same.

[budm]

Re: LG 70LB7100 Led Strip Replacement Question

I am sure that the LCD panel model number is also has revision updated also.