LG 42LE4500 PSU Replaced Backlight Failing Again

[steocullen91]

My uncle has this LG TV since 2011 and about 2 years ago the screen started flickering brighter and darker in the top right corner then eventually that corner just stayed dark. He hasn't a lot of money so had to keep using it. Around 6 months ago it just failed altogether where the screen would light for 2 seconds and then the whole backlight would go out. I had a look at the TV for him and after inspection I just got him to order a replacement PSU because his looked all black and brown etc. I put the new one in and the TV seemed fine. I thought the bottom left and bottom right corners were a bit dark but he said it wouldn't bother him. Anyway it started the flickering brighter and darker again 2 months later and now a patch in the top just slightly to the right of the centre is gone dark again.

I'm assuming it's the PSU going bad again since the LEDs that we're originally out started working again after the replacement which rules out the LEDs. Is it possible the replacement PSU just happens to be also going faulty?

I'd suspect if LEDs were bad they'd either never work or would short and take the backlight out again on startup but since it basically temporarily worked I'm thinking the PSU is just going bad again.

Just a bit weird if it's the same problem again. Anyone else work on one of these sets?

PSU model is yp42lpba with the code EAY60803202.

Thanks.

[dick_barton]

Can you post pictures of your circuit boards especially the led driver board attached to the power supply.

[steocullen91]

Originally Posted by dick_barton

Can you post pictures of your circuit boards especially the led driver board attached to the power supply.

I can get you a new picture when I'm over there probably tomorrow but this is the original PSU that was in it when it failed.

[dick_barton]

On the Led driver board I would test Q401, Q402, Q411, Q412 etc. all the ones that look as though they have well and truly overheated

[steocullen91]

Originally Posted by dick_barton

Can you post pictures of your circuit boards especially the led driver board attached to the power supply.

Originally Posted by dick_barton

On the Led driver board I would test Q401, Q402, Q411, Q412 etc. all the ones that look as though they have well and truly overheated

I'll have look when I'm over. I'll see if the new one is burning out also. I'll bring over the multimeter and check them out to see if it'll be a cheap fix. I wouldn't mind replacing the whole psu again only what if it does the exact same thing again. The entire psu isn't too cheap either.

[dskall]

I suspect you have bad led's

[tom66]

Guess here since those transistors are COOKED that you have bad LEDs in the backlight.

Those transistors regulate the current between strips on the panel by dropping voltage, but if the strips have shorted LEDs in them, then they will have to drop a lot more voltage to make up the difference.

Then they will begin to cook (because if the current is the same but the voltage is much higher, they will have to dissipate a lot of power.)

[steocullen91]

Originally Posted by tom66

Guess here since those transistors are COOKED that you have bad LEDs in the backlight.

Those transistors regulate the current between strips on the panel by dropping voltage, but if the strips have shorted LEDs in them, then they will have to drop a lot more voltage to make up the difference.

Then they will begin to cook (because if the current is the same but the voltage is much higher, they will have to dissipate a lot of power.)

Probably not worth while fixing again then when it fails since the lcd will probably just get broken trying to change the LEDs. It's just to the right of the top centre an LED is gone dark again. It's like a dark U shaped patch. It worked for a month then he said it started to flicker again so he just lowered the backlight and it stopped having problems then for 2 months until that patch went dark again.

It has 2 connections for the leds. One for the left half and one for the right half. It does look like the leds were all lit when I fixed but it just had kind of bad uniformity on the bottom corners. It's really noticeable when an led goes dark.

Can they still be bad leds even if they're lit up and would it really last that long with a shorting led? First time it lasted 2 years since the first flicker.

If they're bad it might make sense to just sell the tcon board when it fails again. I thought LG would be better than that. The Walker Vestel TV I talked about in my other thread still works perfectly and it was my fault I broke it and had to fix it. Surely a brand like LG should last a lot longer than a cheaply made Vestel. Kind of weird especially since the Walker spent nearly 6 years over a fireplace also.

[dick_barton]

It looks like the led controller mosfets took the strain of the leds going faulty as tom66 said and is why they appear cooked.

I see no reason why replacing the led strip should cause any problem, however the led driver board may now be damaged.

http://www.ebay.co.uk/itm/LED-BACKLI...UAAOSw3mpXIpdx

[steocullen91]

Originally Posted by dick_barton

It looks like the led controller mosfets took the strain of the leds going faulty as tom66 said and is why they appear cooked.

I see no reason why replacing the led strip should cause any problem, however the led driver board may now be damaged.

http://www.ebay.co.uk/itm/LED-BACKLI...UAAOSw3mpXIpdx

I thought it would've been hard to replace. Yeah I'd imagine it's a bad strip since it happened again even with another PSU. Even though all the leds were lit they're probably draining a ridiculous amount of current somewhere. I'd imagine I'd have to replace 2 though since it seems to be lit from both the top and bottom from what I can see.

I thought the lcd could break trying to change the leds but maybe that's only with certain TV's. Only thing is I'd have to replace all the mosfets or just get another replacement power supply also. It's better than wasting a TV if it does end up working properly in the end.

[kc8adu]

multiple shorted leds on multiple strips.
not uncommon.
the increased drop across the regulators is cooking them as mentioned earlier.
if you fix it update the firmware as change were made to prevent this.
lg pushes the leds too hard.
and you can replace the mosfets rather than the board.

[steocullen91]

Originally Posted by kc8adu

multiple shorted leds on multiple strips.
not uncommon.
the increased drop across the regulators is cooking them as mentioned earlier.
if you fix it update the firmware as change were made to prevent this.
lg pushes the leds too hard.
and you can replace the mosfets rather than the board.

Right thanks everyone. I'll see what he wants to do and if he just replaces the tv I'll buy it off him and repair it myself. Probably was caused by the leds being driven too hard in the first place as you say and the firmware was probably never updated on the tv either since he got it. I think the backlight was always on 100 too but it had to be the first time it was failing otherwise it kept flickering between dim and full brightness even though it was down which I suspect was the uneven load on the driver board. It's still going to cost over 100 to fix it but it's still about a third of the price of buying an equivalent TV or actually less considering an LG like that would probably cost near 500 still.

[JonathanAnon]

Hi everybody.

I have one of these with the same fault. And I live in the same place, Leinster, Ireland!

Mine looks the same, MOSFETs looked like they have been through a deep fat fryer, and the backlight comes on and shuts off. However, when I plug out the backlight, I get 65.9V across the positive pins going to the LEDs.



So it seems that even though the MOSFETS don't look great, and the plastic that surrounded them looked singed, they are actually doing their job. I checked the LED strips and they look cracked and burned.

what do you think guys, is it worth throwing new LED strips in to this, or just shorting across the dodgy LEDs?

[dick_barton]

It would be worth checking the cost of replacement strips to aid making that decision.
You may get away with shorting across a faulty led(s) but I would consider that the strip would be living on borrowed time.

[JonathanAnon]

I've been pricing the strips online and they are about 50 euro (incl shipping) for two (four in total) to get replacements. I was hoping for cheaper. I'm not sure I'm going to invest that in this TV. The existing ones don't look good at all. The first LED on at least two of the strips show significant signs of burning.

I'll pull them out and test the individual LEDs.

[dick_barton]

Would you be confident in replacing the individual leds. Plenty of Youtube video's showing how to do it.
I am sure that some forum members could advise you how to obtain suitable replacements.

[JonathanAnon]

I paid 40 for it, I was hoping it would be just a small issue. Obviously the good fix is to replace the LED strips, but I don't want to lose my shirt on it!

I'll pull the LED strips off and stick up a few photos. Might help somebody else.

[diif]

If you're prepared to wait a little you can get a set of four LED strips from China for about £25.

[Repair_dane]

Originally Posted by diif

If you're prepared to wait a little you can get a set of four LED strips from China for about £25.

You should be prepared for a long wait if you do this.
I ordered new LEDS 26.04.2020 on aliexpress and paid extra for faster shipping So I would get them after 14-23 days. I am still waiting for them to arrive

[diif]

Some stuff is slow, other stuff is arriving in 2 weeks.