How do you trace a voltage issue on a LG monitor (34UM95c-PD)?

Hello Gang!

Short time lurker, First time poster. I got this LG ultrawide monitor from work, and I’m just super curious about trying to do some DYI fixin’.

So the story is this. This monitor power adapter works (tested on other screens). And I was able to take a voltage reading at the power adapter port, and on the main power switch. If I plug the screen into my laptop the screen registers, but there is no image on the screen, no flicker, no nuthin’.

When I open it up and take a look at the board, i don’t see any obvious signs of capacitors being damaged, no burning or other damage marks.

So i know i have 19V power from the adapter making it through the power switch, and the computer is reading that the monitor SHOULD be there. Is there a place i can get schematics of these things and try to figure out where to go next?

  1. Check the USB ports for 5V presence

  2. Using a flashlight, is there anything visible on screen when plugged in?
    Second thought: Since there are two separate backlight-drivers, I doubt the entire panel to go dark.

  3. What does the underside of the board look like? I may be blind since I do not see anything to generate 5V for the USB ports.

Yikes! I was expecting an email notification or something to pop. I didn’t see that you’d replied. I’m purchased a USB tester to check the voltage out of the port.

The back of the board is pretty bare. I don’t see anything that sticks out on the backside either. No spark marks or burned areas.

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OK. So I tried the USB tester. All 3 USB ports are dead, no voltage. I checked the dongle against my computer and it worked (hooray).

Is there any way to double check the voltage coming in/out of the switch on the back of the TV? I tried flicking it a few times with no response.

Also, Talked to IT. Turns out they had a couple other people turn in their monitors after power outages.

Well, hmm…

In case you have a multimeter on hand, you can probe back here for voltage:
image
If that reads 0, the Powerbrick is dead.

If you know the power brick is good the next easiest thing to look for is a blown fuse. They may visually look fine but still be open.

So there is voltage at the power brick but i cant get voltage at the switch next to it ( i do t even know if these pins would be the right place to check). Been doing some googling and having a hard time understanding what a chip fuse looks like? Is it these sandwich looking deals? None of them look bad. I checked the capacitor just above it and it is giving me 19v. How do i tell which of these fuses to tedt next?


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What you’re describing sounds like a capacitor.

The easiest way to find a fuse is by reading the silkscreen on the pcb. A fuse will probably start with an F. You check if it’s good by either measuring continuity without power connected or by measuring voltage on both sides with power connected (should be the same voltage on both ends).

Those components in your picture are probably inductors. I believe that’s what the L designates, anyway.

That switch won’t necessarily have 19v going to it. There’s a good chance that it’s a much lower voltage that is provided by one of the chips on the board.