LG 55LM4600-UC Backlight Shuts Down

[squeaks]

I am working on LG 55LM4600-UC and LED backlight shuts down after a few seconds. Audio normal. LED on main board EAY62512801 blinks three times and stops and than repeats. Checked main electrolytic caps and they are okay. Since I am not very familiar with this model, could I get some troubleshooting tips. Thanks! Mike

[ReeceyBurger123]

Re: LG 55LM4600-UC Backlight Shuts Down

Done any research on testing the Led voltages ?

[vinceroger69]

Re: LG 55LM4600-UC Backlight Shuts Down

This video may give you a idea how to check the led voltages etc if have have problems post a picture of the led connector area of the power supply then we maybe able to tell you what pins etc to test. What power supply does this set use?
https://www.youtube.com/watch?v=Bf5T2wwtydY

[squeaks]

Re: LG 55LM4600-UC Backlight Shuts Down

The LED+ voltage to ground is 78 volts than drops to 71 volts after backlight shuts down. While the backlights are lit for about 5 seconds, the V1, V3, V5...are about 8.7 volts to ground. After backlight shuts down the voltage is about 20 volts to ground. With LED sockets removed the voltage is about 102 volts to ground at LED+. Thanks for your help.

[squeaks]

Re: LG 55LM4600-UC Backlight Shuts Down

I have the service manual for 55LM4600; however, does anyone know how that I can get the power section schematic? Thanks, Mike

[budm]

Re: LG 55LM4600-UC Backlight Shuts Down

You need to find out if the BL-ON and the DIM control signals are still present or not when the backlights drop out.
This TV has 12 strings of LEDs, the Vxx pins are for the Cathode retun lines for the LED strings.

[squeaks]

Re: LG 55LM4600-UC Backlight Shuts Down

Here are additional voltage information; I am assuming that I have a bad LED on string 6.

Voltages for each LED String measured at board pins (volt to ground):
Backlight on..........Backlight off
LED+ 78.8.............71.3
VC 1 8.4..............19.8
VC 2 8.2..............19.5
VC 3 8.6..............19.6
VC 4 7.7..............19.7
VC 5 8.4..............20
VC 6 1.3..............24
VC 7 8.6..............19.9
VC 8 8.4..............19.9
VC 9 8.6..............20
VC 10 8.6..............20
VC 11 8.4..............20
VC 12 8.9..............20