LG 42LE4500 Losing Backlights

[tom66]

Re: LG 42LE4500 Losing Backlights

Turns out it has a dead panel (see other thread.) If you want any boards, let me know. I think it's slightly different to yours. I've got £45.00 in it but also have stand but no remote.

[newtothis]

Re: LG 42LE4500 Losing Backlights

What a **** eh... I've only ended with one bad panel so far but sold the boards for more than I paid for the T.V so wasn't fussed.

Whats the P/N of the PSU please Tom.

I would rather get this done on component level but... if it comes to it I may want that PSU off you!

[tom66]

Re: LG 42LE4500 Losing Backlights

Yours has the LED driver on the PSU board? Mine has a separate LED driver running off 24V, so unfortunately I don't think it's compatible. There's a chance you could mod it in, but I wouldn't know.

[newtothis]

Re: LG 42LE4500 Losing Backlights

Ah, yes mine is integrated with the PSU... I'm sure I can solve this one anyway... voltages going into the LCD Driver are correct, whats coming out isn't... just hoping its not the controller IC that's gone.

Cheers though

[tom66]

Re: LG 42LE4500 Losing Backlights

The only thing that I noticed on your board is what looks to be "mod" resistors in place of some of the transistors. No idea if that's a sign someone else has fiddled or a factory mod.

[newtothis]

Re: LG 42LE4500 Losing Backlights

Pretty sure its factory done, Don't ever think this set had been opened before I had it... the LED connectors state blanks and these correspond with the transistor blanks.

Ok a little input please Tom, I got my SMD station out and removed the 474 resistor from the first line and the second on the LCD driver... out of circuit they read correct... in circuit the second reads 100ohm below...so something on this line is not right... reading on the transistor in circuit shows the same value as in my above post.... next in line is another resistor which reads correct....

so in circuit on the faulty line - 1K resistor (reads correct) traced to transistor (reads incorrect) traced to 474 resistor (reads incorrect) traced to LED connector (had unplugged)

If i leave the set for a while before switching it on it will stay on for 2 minutes, after that it lasts 2 seconds... when the set is working the DC is correct throughout all the lines but as time goes on the voltage starts to drop on 3 lines.... at that point the backlights turn off.... upon switching straight back on the DC then rises to 33v in 2 seconds before switching the backlights off.

any ideas where to look?

[tom66]

Re: LG 42LE4500 Losing Backlights

In circuit measurements are nortoriously unreliable. I'd get a can of freeze spray and start spraying the board carefully. It's obviously something temp sensitive. See if you can narrow down the exact point.

Poundland sell cans of compressed air, 200ml for £1, half the price of eBay. These can be used for freeze spray by inverting the can.

[newtothis]

Re: LG 42LE4500 Losing Backlights

OMG! Guess what the problem was Tom??... I have the set working now

[tom66]

Re: LG 42LE4500 Losing Backlights

Loose connector?

[newtothis]

Re: LG 42LE4500 Losing Backlights

Nope, nothing in the hardware! I always check connectors

Software fault... never even thought about software! Held a flashlight to the screen and got into the settings... factory reset and voila!

Thanks for all your help though Tom, As always its very much appreciated!

[tom66]

Re: LG 42LE4500 Losing Backlights

Nice one, very surprising though!

[scooter13uk]

Re: LG 42LE4500 Losing Backlights

I've been messing with mine with same fault for last few days....will only stay on for a couple of seconds. Just tried a factory reset and stays on for 30 seconds...this must surely indicate a software fault? Any ideas?

[newtothis]

Re: LG 42LE4500 Losing Backlights

Tv has come back... Original fault.

Resetting the software makes no difference now.

100% the issue is within the LCD driver components of the PSU. Error reads 3v once the backlights trip out... Took a risk and disconnected the error lead from the driver to the PSU... LED strips still go out and 3 v is being emitted to the pad that carries the error signal to the PSU.

So I tried freezing the drivers... nothing.

Heated them up... and the backlights dont even attempt to turn on.. but as it cools they light up then go off again as usual... narrowed the heat to the driver IC. So IC is dead

Looks like the only repair for this issue is replacing the PSU which is a heavy cost of ~£100!

Looks like I am parting this one out.

[ReeceyBurger123]

Re: LG 42LE4500 Losing Backlights

Its not the Ics its something around them that fails I cant fucking find out what, going to start isolating parts.