Lg 42LE4500 losing backlights

[Greasejunky]

Hi all,

Mechanic from Norfolk trying to keep his old tv alive

I've lurked around for a while and read up so much my head hurts and now I have a couple of questions.

Symptoms:

Tv starts and shows logo. Sometimes the backlights will stay on for around 10 seconds but mostly around 2-3 seconds.
I've done the flashlight test and can see the screen and menus etc.

What I've done so far...

With a flashlight I've gone through the menus and reset to factory settings. No fix.

Stripped the set and looked for a bad led. All work fine and there's nothing obviously wrong. Reading up on here a tech doe say this set won't shut down for one bad led anyway.

The psu is looking suspect after the above tests as this has the led driver built in. Well on top anyway.
Now these are £70+ and getting old so I read up many threads and seen there's a common issue with the LED ic chip.

Can you get these? Probably not. I did reflow the solder on the chip legs using an air solder station. No fix.

Now there's a thread on here that I will edit a link to shortly - https://www.badcaps.net/forum/showthread.php?t=44340 that states the driver board can be removed? With some work the leds can be driven direct at a lower voltage. Can anyone give me some guidance on this including pictures if possible?

Another member states the fitting of a 10k resistor fitted to pin 16 then to ground fixes this issue? Again guidance would be much appreciated.

I'm not an electronics tech expert. I'm a mechanic but I can solder, follow tracks and figure out the basics fairly readily.
I've repaired PS4 HDMI ic problems before etc.

Please can someone who knows the know help me out?

Thanks

[ReeceyBurger123]

Re: Lg 42LE4500 losing backlights

Replace the driver Ic or the whole the board.

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Thanks, do you know where I can get an ic for this set?

[vinceroger69]

Re: Lg 42LE4500 losing backlights

whats the part number printed on the ic

[Greasejunky]

Re: Lg 42LE4500 losing backlights

So the larger ic chip is AS3693B 1018VAB

I think this is used to control the dimming? When the set starts to auto dim is when the leds shut down.

The smaller ic is MEGA4BPA or possibly MEGA48PA AU 1022

Thanks

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Can anyone explain why adding a 10k resistor from pin 16 to ground could work?

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Can anyone help me?

#all by my self......

[budm]

Re: Lg 42LE4500 losing backlights

Spec sheet of that IC to find out what pin 16 function is?

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Can't fine the correct one.

I've linked some threads but I'm getting the feeling newbies aren't that welcome?

I'm a mod on another forum for mechanical issues. Maybe I'll stick with that lol

[budm]

Re: Lg 42LE4500 losing backlights

Can't fine the correct one.

I've linked some threads but I'm getting the feeling newbies aren't that welcome?

I'm a mod on another forum for mechanical issues. Maybe I'll stick with that lol

It is nothing to do with welcoming, it is the missing info. The person indicated in the link did not say pin 16 of what, the IC (which one?) or the connector (which one?) and no follow-up either as to what exactly what he did and did not share the info which is what this site is about.

[vinceroger69]

Re: Lg 42LE4500 losing backlights

AS3693B led controller ic data sheet

[budm]

Re: Lg 42LE4500 losing backlights

Pin 16 is the GATE3 (one of the 16 Gate drives (GATE 1~16) output to drive the external MOSFETs for each string of the LEDs), so he grounded the drive output which means one of the 16 LED string will not be on, so when he said the LEDs are ON then that will be impossible.

[PorkfriedPanda]

Re: Lg 42LE4500 losing backlights

Can't fine the correct one.

I've linked some threads but I'm getting the feeling newbies aren't that welcome?

I'm a mod on another forum for mechanical issues. Maybe I'll stick with that lol

They seem reasonably welcoming to me. They're not necessarily sunshine and daffodils but shit, it's a forum about fixing electronics so I didn't really expect that.

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Sorry guys.

[vinceroger69]

Re: Lg 42LE4500 losing backlights

i cant find much info for the smaller ic thats mentioned unless its a ATMEGA48PA AU ?
maybe some clear pictures of the ics will help us identify them.

[vinceroger69]

Re: Lg 42LE4500 losing backlights

Sorry guys.

No need to be sorry we will always try to help but if we havnt worked on these boards ourselves we also go off infornation etc provided by others but some times people dont update there threads or take notes of repairs etc due to being busy but bear with us we will try to help.

[Greasejunky]

Re: Lg 42LE4500 losing backlights

I appreciate your efforts thank. I'm full of flu so a bit like a bear with a bad tooth.
Not only that but it's full blown MAN FLU lol

The smaller ic seems ok, I'm going to try and replace the larger ic and see if it helps.

I've found one on eBay in china so should be able to update the results in around 6 weeks.

Failing that I'm very interested in running this sets leds at the lower voltage by removing the board altogether. Hopefully the guy who figured that out could give me some pointers.

Thanks again.

I'll go play in my bin # oscar the grouch

[vinceroger69]

Re: Lg 42LE4500 losing backlights

maybe if you have some time upload some clear pictures of the board some of the front some of the rear of the pcb as clear as you can get them so we can zoom in on the pictures etc that may help with fault finding/repair and alastair may remeber the repair but if its been a while hes probs fixed a fair few since then so maybe hard to remember all the details i guess.

[Greasejunky]

Re: Lg 42LE4500 losing backlights

Sounds good, will give it a go

[citywidetvtech]

Re: Lg 42LE4500 losing backlights

I am terribly sorry for the confusion. I must have had a few LG backlight trouble threads open at the same time and posted my ramblings onto the wrong one. I apologize for any grief i've caused. That chip on the one I was referring to was a BD9483F, and the Pin I was referring to is the fault output pin. I found a fault output pin for the CORRECT CHIP you guys are using if you want to try it and see if there could be similar results. Its #44. Sorry again for the confusion, will be more careful next time.