LG 42LB5600-UZ sound but no backlight

[Ifixstuff9]

I have an LG 42LB5600-UZ. When I connect the TV to a video source I can hear sound and I can see an image when I do the flashlight test. If I open the TV and measure the voltage coming from the power board to the LEDs I get nothing. I'm pretty sure I have a bad power board.

So, here are my questions:
Is there any way I can test the back light before ordering parts?
Is there a way I might be able to repair the board? The fact that the backlight has absolutely no power yet the rest of the TV works fine leads me to believe that it might just be one bad component that needs to be swapped out.

[dskall]

Re: LG 42LB5600-UZ sound but no backlight

Assume led's. Not enough pictures to see. You have no 24v

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

Whats pictures do you need? I can add more if you want.

[dskall]

Re: LG 42LB5600-UZ sound but no backlight

Whole back of tv. The rest of the boards. Close up of connectors

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

Here are the pictures you asked for.

[attainteddragon]

Re: LG 42LB5600-UZ sound but no backlight

since you have a pic on screen but no backlights, you are looking at an led failure unless there is no voltage on led+, but it is an lg and will almost always be led failure in this situation.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

I have no voltage on LED+, hence my suspicion that the power supply is bad. I did some research on this model and it seems like replacing the power supply is a common fix for this model.

[budm]

Re: LG 42LB5600-UZ sound but no backlight

Turn TV off, set DCV meter to 600VDC range, then put DCV meter's black probe on the chassis and red probe of the meter on the LED+ pin of the LED connector, keep an eye on the meter then turn on the TV to see how high the Voltage goes up to then wait about 5 seconds to see how low it goes down to.
https://www.badcaps.net/forum/attach...1&d=1499898761
BTW, the solder joints for D201 (this one supplies the B+ to the Voltage boost converter for the LED power supply section), D208 do not look good, you can see small ring around the legs. I would re-solder all the transformer legs and all the legs of the devices that are mounted to the heatsink too.
LG EAY63071904 Power Supply / LED Board.
http://www.shopjimmy.com/lg-eay63071...led-board.htm#

[dskall]

Re: LG 42LB5600-UZ sound but no backlight

Need voltages from connector that goes from power supply board to main board. Will need pin#- PIN DESCRIPTION -Pin voltage in standby-Pin voltage when pushing power button and picture of connector on power supply board.
Format:
Pin# - Pin Description - Pin Voltage standby - Pin voltage power on
1 - XXXXXXX - XXv - XXXv
2 - XXXXXXX - XXXv - XXXv
3 - XXXXXXX - XXXv - XXXv
4 - etc.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

Sorry I didn't reply until now. I just went ahead and ordered a new power supply, something came up and I don't have time to work on the TV anymore. Tomorrow I might take a look at the power supply and re-solder those connections if I have the time.

[budm]

Re: LG 42LB5600-UZ sound but no backlight

BTW, when you measure the LED+, what did you use for the GND reference?

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

I was using LED- as a reference. I decided to use the chassis as GND reference and I got 114 volts. So, I guess that means the back light is bad?

[budm]

Re: LG 42LB5600-UZ sound but no backlight

Did you do the test as instruct by watching the Voltage to see how high it goes up to before dropping down to 114VDC? That is important to find out of the Boost converter starts at all.
The LED Voltage should be around 200V with working LED (as printed on the board), but it will go up a lot more higher than that if the LED string has open circuit. Right now the feeding Voltage to the Boost converter looks to be 114V as you have measured.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

I did the test. When I first power on the TV I get 248 VDC, but that voltage drops down to 104 VDC shortly after.

[budm]

Re: LG 42LB5600-UZ sound but no backlight

I did the test. When I first power on the TV I get 248 VDC, but that voltage drops down to 104 VDC shortly after.

OK, that is what I want to see when the TV is first turned on which is VERY important info when troubleshooting LED backlights problem because opening up the LCD panel is the last thing you will want to do. Time to open up the panel to get to the LED strips and wiring.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

The panel type is T420HVF07.1, and its made by AU Optronics. I found a replacement LED kit for the panel on shopjimmy.com, but its out of stock. Will any other led strips work or does it absolutely have to be one for the T420HVF07.1 panel?

[budm]

Re: LG 42LB5600-UZ sound but no backlight

The strips have to match panel otherwise they may fit or work properly, IE same amount of LEDs and Voltages/Current requirement.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

Ok, I'll just wait until I can find an exact replacement.

[jbfr_54]

Re: LG 42LB5600-UZ sound but no backlight

Why don't you try replacing individual LED's ? It's not so hard and a lot lot more economical (about 10 cents each LED replaced). I personnally ordered LED's 3528 rated at 400 mA form Aliexpress and repaired several Toshiba, LG and Samsung TV's using these. A lot of posts explain how to, even youtube movies describe how to proceed. The most critical is to open the screen to access the strips. You have to test each LED using a multimeter by removing a bit of white painting on the strips PCB lanes to allow electrical contact with probes (try both polarities for testing). When each defective LED is identified, do not remove the strips from the screen chassis, remove the lens using a cutter, then the with plastic cache. Use a thermal gun to gently warm the LED that should be freed and move away. Use soldering flux to ease resoldering of new LED (using a magnifying lens is a good idea). Hold the new LED in the correct position (polarity and well above solder pads), heat each pad from side of LED to make solder stick to LED pads together with the PCB pads. It is not always nécessary to add solder as the flux will ease the existing solder on the PCB to move to the LED. DO NOT HEAT TOO LONG THE LED, IF NOT OK IN FEW SECONDS WAIT A BIT AND RETRY. Mke sure that the LED is now correctly soldered and functionnal. Glue the cache back in place, the lens (using cyanolide glue on the 3 plastic pads of the PCB), make sure the lens is aligned with the LED.
You better try as anyway your strip(s) is bad, it will cost you only the buying of the LED's (about 10$ for a hundred).
Good luck.

[Ifixstuff9]

Re: LG 42LB5600-UZ sound but no backlight

Sounds like a good idea, I might as well give it a shot because the LEDs are so cheap.