LG 42LB5820 TV turns on randomly and whenever it wants !!

[Terrotiste]

Hello everyone ,


Yesterday during the deposit of furniture in the place provided for this purpose for the removal of bulky, I found a tv LG 42LB5820 ... in his box well packaged, with his feet, but without the remote control ...


I took her home to see what she saw that she was in an extra clean condition


When first connected to the 220V, the TV displayed the LG logo moving on the screen with the message underneath the "unscheduled" logo


Having thought it was fully functional I disconnected to mount it in a room to connect to a box HDMI and see if I had a picture ...


Connected to the box, the TV turned on, showed its logo, then cut in 5 seconds ...


I then tried again to turn off the 220 V and turn on the TV again, but it was without any effect, no more starting the TV ...


Walking through the canvas I could read that the worry came from the capacitors of the power supply, I opened the TV.


After visual inspection, no chemical capacitors appear inflated or distorted ...


This morning in the tear, after disconnecting the TV multiple times I have a stealth screen ignition ... then nothing


Can someone give me some research leads, it would make me sick to throw a 42 inch trash. Especially as I personally have in the living room only a 40 inch that is 12 years old ...

For information I reconnected the tv, it turned on for 3 seconds with the logo LG then it cut


Thanks a lot for your help

Best regard

[budm]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

1) Please upload good clear pictures of the whole backside of the TV showing all the board and then good clear straight shots pictures of the whole power supply board.
2) What kind of Voltage testing have you done of the power supply connector that goes to the main board? What are the Voltage readings for each pin when TV is OFF and when TV power switch is activated?

[Terrotiste]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Good evening

Thank you for your reply . I already post a photo of the power card and the main board ...

Tonight I reconnected the TV, it restarted and displayed the LG cube for 3 seconds and then cut again, black screen ...

Are the voltages on the output connector of the power suplied board to be made with the connected or empty hand board?

Thank you very much for your help, because I have very little knowledge in the world of TV. It's not my job ...

Jerome

[Diah]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

you have LED back light issue. one or more shorted

[neilc6]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

LG displaying the logo and then the backlight turning off is the standard symptom of bad LED backlights in LA, LB and LN series TVs. The circuitry detects a problem and shuts down the backlight.

[saddle_au]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Shorted backlight leds. Over-current to the panel from the led driver. Led driver connector on top of power supply board in your photo which has two black wires LED+ and LED-.

If you want to know more or be more sure before a dissassembly, you can test this with one of the backlight testers from ShopJimmy, Amazon or one of the china listings. It should be able to light up the panel for you.

Now the hard part. You need to get to the led strips to either replace all the strips or to find and replace the individual bad leds. The back comes off, then the bezel, the metal frame, the lcd screen, the plastic retainer, the diffusion sheets and the white reflector sheet. All of these need to be handled carefully especially the lcd screen (it breaks easily) and the diffusion screens (they mark easily). Any marks or dirt/fluff on the screens is visible when running the tv. If you hurt the pcb attached to the lcd or the tabs between them, it's game over.

If you dissassemble and decide to buy strips, you either have to store the dissassembled tv or put it back together while you wait. It's a trade off, the longer it's apart, the more likely something will hurt or mark those screens. The more you assemble/dissassemble, the more likely you'll do something to them. If I have to wait and don't want to assemble, I place them between 3 large cardboard sheets and stack them away. One slot for the panel and the other for the sheets. The diffusion sheets need to go between cardboard as well as they tend to not stand vertically under their own weight and will flop over risking marks.

Depending on what you want it to cost you, replacing entire led strips is better but much more costly than replacing individual leds. Because so many have died causing the shutdown, you don't know the remaining life of the working ones. You could be doing this again in a month or so. But leds are cheap, especially if you have access to dead tvs with cracked screens.

www.youtube.com/watch?v=h5Zyqowl6zg

Good find, good luck.

[Terrotiste]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Good evening


Thank you all ... After changing the LED bars, the tv works ....


However I have in the middle of the tv a priori pixels extinct (black)


Is it possible that when I dismounted the slab of the tv, and that I put it on the table, a crap was stuck behind, and that would hide these 2, 3 pixels missing on the mage?


I wait for your answer before restarting the slab to check


I can pass a photo if needed ...

Thank for your answer


Jerome

[Diah]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Good evening


Thank you all ... After changing the LED bars, the tv works ....


However I have in the middle of the tv a priori pixels extinct (black)

show us clear photo on whole screen and the pixel area you mentioned

[Terrotiste]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Hello

Here is a photo of the spot on the screen that may have appeared after the change of the led bars ... The black dot is this dead pixels, or a dust behind the slab?

Thank you for your answers

Jerome

[Diah]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

dust.. clean it

[Terrotiste]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Hello
I will restart the tv and clean the filters and the slab. As a novice, what are your recommendations for cleaning the filters and the slab? Cloth or produced to make windows? it seems the glass product is not recommended and aggressive
thank you for your help
Good night
Jerome

[Diah]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

this small dust are on the back side of the LCD, use any air press like cold state hair dryer will blowing it out

[Unspun01]

Re: LG 42LB5820 TV turns on randomly and whenever it wants !!

Buy something from an automotive autobody shop called a "tack" cloth. This is a tacky cloth that is used to wipe surfaces before painting to remove lint or debris. It does not leave lint or fibers and does not streak or leave residue.

Automotive grade is best, but also available at many hardware stores:

For example:

https://www.homedepot.ca/product/ben...oth/1000413825


The tack cloth is very useful to clean or lift any lint or dust or hair that may have accidentally been sandwiched between the plastic dispersion layers and the LCD panel.

It holds the lint/particles and doesn't let go.

If you don't buy a tack cloth, you may use a can of compressed air but please note that you may only spread the dust or particle from one area to another.

It is best to re-assemble the panel into a "useable" state before fully re-assembling the TV so you can turn it on and ensure that there are no more trapped particles. This is especially necessary with 4K TVs, where even a very small particle can disrupt light through several pixels and be noticeable/annoying.

Tack cloth can be re-used many times if you place it back in it's package and store properly.