LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

[nomoresonys]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

Ah ok, was wondering why everything but the 5 volt was there so 15 n 16 won't be connected.

[Unspun01]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

You can bridge faulty LED terminals, the ultimate solution that will give you dimly lit areas on the screen.

Honestly, no offense but this is poor advice. Do NOT simply bridge a faulty LED.

According to ohm's law, if voltage remains constant, and the resistance of the LED string is reduced by bridging faulty open LEDs (or even by a shorted LED) then the current through the LED string increases.

Bridging a faulty LED with a wire or solder blob does not "use" any electricity, and does not create an associated voltage drop like an LED. Therefore you will essentially force more current through the other good LEDs in the same series path and result in over-driving the other LEDs until they fail as well.

This is called a "cascading" failure, where one LED fails, which places extra current on other adjacent LEDs, forcing them to fail as well.

If you absolutely have to, remove the bad LED and replace it with a suitable diode or something similar.

Truly the best solution is to replace the LED and diffuser lens cover. This is difficult for most people without proper tools since the LEDs are delicate and don't like direct contact heat from a solder iron.

Another solution I like because it can be done with basic tools is called "stacking". This is where you cut a good LED from a LED strip complete with its attached lens cover, and glue/attach it in place of the original LED that was removed. + and - wires are soldered to appropriate points on the LED strip to restore the circuit. There are no special tools required, and no excess heat which can damage the existing backlight strip or new LED. Very easy for anyone to do. The only concern is observing correct polarity of the LED.

[budm]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

Hi,
I have a LG 55LF5700_UA LED tv

The standby light is on, I can see the picture with the flashlight test, and there is no back light. I test the standby power at the power board and there is no power. The 2 Led+ test points are only showing 30.3 V.

I can not find schismatics for this board but is it possible that there is a separate ground for the standby voltage? Thanks

Power Supply Board ((X)PLTVEW401XAT9) Voltages:

1. DIM: 2.33
2. O/F: 3.34
3.PS: 3.36
ON
4.NC 0.00
5. GND
6. GND
7. GND
8. GND
9. 12v_A: 11.96
10. 12V_A: 11.96
11. 12V: 11.95
12. 12v 11.95
13. 12v 11.95
14. 12v 11.95
15. 5v 0.00
16. 5v 0.00

LED Voltage

+Led 1: 33.3V
+Led 2: 33.3V

1) The power supply PCBA for your TV does not have 5V standby section stuffed with parts that is why there is no 5V (as you can see from the board layout https://www.shopjimmy.com/lg-pltvew4...ply-board.htm#), it use 12V as standby.
2) All the control signals are normal.
3) Put the Volt meter (set to 200vdc scale) probes on the two legs of capacitor C8107 then turn the TV on while watching the meter to see how high the Voltage jumps up to and then wait 10 seconds to see how low it goes down too.
4) To probe the Even number pins, you can use skinny probe to probe from the wire entrance side of the connector.
5) Taking the panel apart is the last thing you want to do after all the testings are done.
Pictures provided by shopjimmy: LG PLTVEW401XAT9 Power Supply Board

[nomoresonys]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

Maybe try unhook cable from powerboard to mainboard and see if your standby voltage comes back.

[Le Fils du Boulanger]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

Open your TV and try to access the LEDs. Attention, very deliquate operation because it will remove the screen. As soon as it is done, remove the light diffusers from the LEDs. Put your multimeter in the diode test position and check if each LED is lit. This will allow you to detect LED bares to be changed. You can bridge faulty LED terminals, the ultimate solution that will give you dimly lit areas on the screen.

[Jermo133]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

Sorry I forgot to add these. Thanks again for the help.

[budm]

Re: LG 55LF5700-UA.CUSDLH - Black Screen, can see image with flashlight test

We need to see the pictures of the backside of the TV showing all the boards and good clear straight shot of the whole power supply board so we can see what we are dealing with.

[Jermo133]

Hi,
I have a LG 55LF5700_UA LED tv

The standby light is on, I can see the picture with the flashlight test, and there is no back light. I test the standby power at the power board and there is no power. The 2 Led+ test points are only showing 30.3 V.

I can not find schismatics for this board but is it possible that there is a separate ground for the standby voltage? Thanks

Power Supply Board ((X)PLTVEW401XAT9) Voltages:

1. DIM: 2.33
2. O/F: 3.34
3.PS: 3.36
ON
4.NC 0.00
5. GND
6. GND
7. GND
8. GND
9. 12v_A: 11.96
10. 12V_A: 11.96
11. 12V: 11.95
12. 12v 11.95
13. 12v 11.95
14. 12v 11.95
15. 5v 0.00
16. 5v 0.00

LED Voltage

+Led 1: 33.3V
+Led 2: 33.3V