LG 55LA6200 Backlight Issue?

[petronm20]

I have a LG 55LA6200 when turned on the backlight turns on the LG logo is displayed then immediately turns off, all inputs and sound function appropriately and verified the image is displayed on the screen with a flashlight. When it turns on the LED power output from the PCB reads a voltage which seems to hit 9V for a second (my multimeter may not be able to refresh fast enough to read the max voltage supplied) but when the backlight turns off the voltage drops to zero. When i turn the TV off disconnect LED power connector and plug it back in the voltages remain the same, power is present for a second the drops to zero. I already tried a new PSB with the same results so wanted to check here to see what you guys think before I order a new main board, I figured since there is no voltage when the LED power output is both connected and disconnected it wouldn't be bad LED strips? Thanks in advance for any help!

[budm]

Re: LG 55LA6200 Backlight Issue?

We need good clear straight shot pictures of the boards and the whole backside of the TV showing how all the boards are connected together.
We need to find out if the LED driver is getting the BL-ON and Dimming signals from the main board or not and also some other Voltages as well.
There are more than one versions of the TV.
http://www.shopjimmy.com/catalogsear...?q=LG+55LA6200

I.E. this power supply board:
http://www.shopjimmy.com/lg-eay62709...-led-board.htm
the Voltage at the LED+ pin (the ANODE of the LED strings) should be around 76V with load, you will have to put black probe on GND and red probe on LED+ THEN turn the TV on to see how high it goes up to.
The 9V reading made at which pin of the LED connector?

[petronm20]

Re: LG 55LA6200 Backlight Issue?

EBT62368508 is the main board. The Power supply board is not the one you linked to it does not have the two connectors it has this board:
http://www.shopjimmy.com/lg-eay62810...upply-unit.htm

[petronm20]

Re: LG 55LA6200 Backlight Issue?

Here is a photo of the inside, it is from another thread on the forum but its identical to the board set / wiring. The post its from (LG-55LA6205 backlight issues) is just the European model and have already searched and the boards themselves are interchangeable.

[budm]

Re: LG 55LA6200 Backlight Issue?

So it has two LED strings, the output Voltage for the LED strings is over 100 Volts per chart printed on the board.
So follow the instruction on post 2 check DCV @ the LED + as instructed and the control signals. Your meter should be fast enough to catch over 100V swing.
We will not be surprised if it has bad LEDs.
LG EAY62810701 (3PAGC10124A-R) PS.
Connector P201:
PWR-ON = PS-ON
DRV-ON = BL-ON
PDIM1 = PWM Dimming 1
PDIM2 = PWM Dimming 2

Pictures provided by shopjimmy.

[petronm20]

Re: LG 55LA6200 Backlight Issue?

Ok, I will do this tomorrow morning. The guy in the post I referred to about the photo disappeared after a reply said he had bad/cold solder joints on the LED strip to strip connectors so I think I'm also going to check that out too... Thanks for the help!

[petronm20]

Re: LG 55LA6200 Backlight Issue?

I am also going to check the LED power connectors again because the 9V made no sense to me too.

[petronm20]

Re: LG 55LA6200 Backlight Issue?

Ok, thanks for the information as the situation has changed at the led power connector P801, I had grounding issues which resulted in incorrect readings. There seems to be something going on with the first LED- at P801 as the voltage spikes then drops but I listed both the asked for voltages at P201 and updated voltage details at P801 below:

VDC at P201:
3.4 - PWR-ON = PS-ON
3.4 - DRV-ON = BL-ON
3.5 - PDIM1 = PWM Dimming 1
3.5 - PDIM2 = PWM Dimming 2

VDC at P801 (Power On):
LED- *: 101 @ power on then drops to zero within 5 seconds of the backlight going off
LED+ : 87 @ power on and is stable within 1 VDC
LED- : 10 @ power on and is stable at 10 with little no fluctuation
LED+ : 87 @ power on and is stable within 1 VDC

VDC at P801 when powered OFF:
LED- *: Remains Zero
LED+ : Drops to 30 quickly and slowly drops to zero within 1 min
LED- : Drops instantly to Zero
LED+ : Drops to 30 quickly and slowly drops to zero within 1 min

[budm]

Re: LG 55LA6200 Backlight Issue?

"VDC at P801 (Power On):
LED- *: 101 @ power on then drops to zero within 5 seconds of the backlight going off
LED+ : 87 @ power on and is stable within 1 VDC
LED- : 10 @ power on and is stable at 10 with little no fluctuation
LED+ : 87 @ power on and is stable within 1 VDC

Both LED+ are tied together and fed by the Voltage booster output.
There is no way this LED- which is the Cathode return of the the LED string to be higher than the LED+ feeding Voltage.
But at this point it does look like you do have LEDs problem.

[chrismurphy]

Re: LG 55LA6200 Backlight Issue?

Faulty LED string , remove screen and check ,replace faulty strips

[tvhelp60]

Re: LG 55LA6200 Backlight Issue?

Following this forum with the same symtoms but different tv (LG 55LN5700-UH), I am about to check voltages at the power supply/led driver connections (LED +). I get 84.4 at both LED+ either with LED connected or diconnected, at first second of two, the voltage reads 200v at first LED+ and 123v at second LED+, then both voltages go down gradually and stabilize at 84.4. Is this an indication of bad LED backlights? Or bad powersupply/led driver board? Any assistance will help and is appreciated.

[budm]

Re: LG 55LA6200 Backlight Issue?

Following this forum with the same symtoms but different tv (LG 55LN5700-UH), I am about to check voltages at the power supply/led driver connections (LED +). I get 84.4 at both LED+ either with LED connected or diconnected, at first second of two, the voltage reads 200v at first LED+ and 123v at second LED+, then both voltages go down gradually and stabilize at 84.4. Is this an indication of bad LED backlights? Or bad powersupply/led driver board? Any assistance will help and is appreciated.

The Boosted Voltage will go up over 200V if there is no load (open circuit) and then the Voltage will go back down (over Voltage shutdown) to the feeding Voltage of around 80V that is fed into the Boost converter circuit.
You need to leave the black probe on the chassis, red probe on LED - one at time, then watch the meter when you turn on the TV to see what you get on the LED -, repeat the test on other LED -.
More likely you will find bad LEDs.

[jmarsh1320]

Re: LG 55LA6200 Backlight Issue?

I have the same issue with the backlight flash, then no picture. I actually got to the backlights, and tested them. They all lit up, so I thought it was the power supply board (LG EAY62810701). After ordering a replacement board, still had the same issue, so I tested all of the voltages per this thread. Any feedback would be much appreciated!

VDC at P201:
3.4 - PWR-ON = PS-ON
3.4 - DRV-ON = BL-ON
3.5 - PDIM1 = PWM Dimming 1
3.5 - PDIM2 = PWM Dimming 2

VDC at P801 (Power On):
LED- *: 0.4 @ power on then drops to 0.1 and is stable
LED+ : 200 @ power on then drops to 86.4 and is stable
LED- : 41 @ power on then drops to 7.8 and is stable
LED+ : 125.6 @ power on then drops to 86.4 and is stable

VDC at P801 when powered OFF:
LED- *: Remains Zero
LED+ : Drops to 30 pretty quickly and slowly drops to zero within 1 min
LED- : Drops instantly to Zero
LED+ : Drops to 30 pretty quickly and slowly drops to zero within 1 min

[budm]

Re: LG 55LA6200 Backlight Issue?

"LED- *: 0.4 @ power on then drops to 0.1 and is stable" You have open connection/LED/connector in that string that is why the Cathode return shows 0V.

[Heschbox]

Re: LG 55LA6200 Backlight Issue?

Replaced main/led driver board and led back lights. Back light flashes on then stays off
VDC at P201:
3.4 - PWR-ON = PS-ON
3.1 - DRV-ON = BL-ON
3 - PDIM1 = PWM Dimming 1
3 - PDIM2 = PWM Dimming 2

VDC at P801 (Power On):
LED- *: 0 @ power on
LED+ : 200 @ power on then drops to 88 and is stable
LED- : 27 @ power on then drops to 0 and is stable
LED+ : 125.6 @ power on then drops to 88 and is stable

VDC at P801 when powered OFF:
LED- *: Remains Zero
LED+ : Drops to 30 pretty quickly and slowly drops to zero within 1 min
LED- : Drops instantly to Zero
LED+ : Drops to 30 pretty quickly and slowly drops to zero within 1 min

[neilc6]

Re: LG 55LA6200 Backlight Issue?

Replaced main/led driver board and led back lights. Back light flashes on then stays off

You still have a bad backlight or a bad connection to them. Always test your backlight before reassembling. The TV will turn on with the panel disconnected. Video record the flash and step through it frame by frame to find the bad strip or string if you don't have a LED tester.

[BeetonTV]

Re: LG 55LA6200 Backlight Issue?

Maybe I can shed some additional light here:

I replaced a whole set of LED's and they would not turn on. I checked the ps output voltages and they agreed with the above post. Except the cathode return voltage was zero. I tested the backlight assembly with a separate tester, worked just fine. Yet when connected to the tv, the cathode (-) return was zero.

I found the reason for this was the replacement diodes were 6 volts each. The originals measured 3 volts each. Correct part numbers but fake parts? Mistake at the factory?

I repaired and reinstalled the original 3volt diode strips and it works fine.

[dskall]

Re: LG 55LA6200 Backlight Issue?

Maybe I can shed some additional light here:

I replaced a whole set of LED's and they would not turn on. I checked the ps output voltages and they agreed with the above post. Except the cathode return voltage was zero. I tested the backlight assembly with a separate tester, worked just fine. Yet when connected to the tv, the cathode (-) return was zero.

I found the reason for this was the replacement diodes were 6 volts each. The originals measured 3 volts each. Correct part numbers but fake parts? Mistake at the factory?

I repaired and reinstalled the original 3volt diode strips and it works fine.

Interesting. I will keep that in mind.

[neilc6]

Re: LG 55LA6200 Backlight Issue?

The 55 inch LA and LN series uses the thick LEDs same as LB LF series. I have only encountered 6V LEDs on LG 32 inch LB series. All the new strips on aliexpress and eBay are substitute strips since these models are from around 2013.

[jojo88]

Re: LG 55LA6200 Backlight Issue?

All the new strips on aliexpress and eBay are substitute strips since these models are from around 2013.

What does that mean?? All LED strips from anyone except LG are “replacements”.

Do you mean that strips from Ali & eBay are not 3v? Or…?

Please clarify.

Thanks.