Lg 42ln5300 tv won't turn on. Power supply might be ok?

[Snype32]

Hello all, I'm working on a lg 43" LCD. When it's plugged in , the red light fades in and out twice an then stays off. When the power button is pressed, the red light stays on. When pressed again, red light goes out and backlight seems to flicker a bit, but never comes on. I have checked the voltages on the power supply, 3.25 at per on, 3.45 at pdim, 3.45 at n.c. 23.3v at the 24v pin, 12.03 at the 12v pins. The voltage to the LEDs jumps around between 60 and 75 volts, which is where I think the problem is. What should I look for next? I have tested all the smaller caps, and the seem to be ok.

[neilc6]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

LN series known for bad backlights. Get an LED tester or just replace all of them. If you plug it in with the panel off, you should be able to see which strips are out when they flash on before shutting down in protection mode. Lower backlight level to 60 after repair and do it for all inputs.

[Snype32]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

looks like that was it... I took it all apart and found a burnt led. Not sure its worth fixing at this point. Thanks for the info tho!

[neilc6]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

$30 for new strips

https://ebay.us/MZQDZe

[Snype32]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

Hmmm that's cheaper than I thought it would be. Thanks!

[caphair]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

Hi I’m having similar issue except with mine after the standby light blinks twice and fades out. It never stays on and no response from power button.

I have all voltages and at led connector it’s steady at 125v at the + side and 20v at the negative side. If I unplug the led connector the + side still same at 125v but 0v at the negative side. Led strip issue?

[ngth82]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

Hi I'm having similar issue except with mine after the standby light blinks twice and fades out. It never stays on and no response from power button.

I have all voltages and at led connector it's steady at 125v at the + side and 20v at the negative side. If I unplug the led connector the + side still same at 125v but 0v at the negative side. Led strip issue?

Can you confirm the SMPS board number you have on your TV? Doing a quick search on shopjimmy, I'm going to assume your TV has SMPS board model number EAX64905301.

Do you see the backlights flicker at all when you initially plugin/turn on the TV? You should be able to look at the metal chassis holes and see if it illuminates - even for a split second.

The LED string is wired in series - you can see this if you look at the back of the SMPS board @ Connector P801. The middle two pins are connected to each other.


Are you measuring the voltage from VLED+ to VLED-? Or referenced to ground? Given that you read +125V, my guess is that you have at least one open LED. Do you have an LED tester? Might be time to open up the panel and have a look for blown LEDs.

Do you get the proper voltages on the connector from the SMPS to the main board?

[caphair]

Re: Lg 42ln5300 tv won't turn on. Power supply might be ok?

Can you confirm the SMPS board number you have on your TV? Doing a quick search on shopjimmy, I'm going to assume your TV has SMPS board model number EAX64905301.

Do you see the backlights flicker at all when you initially plugin/turn on the TV? You should be able to look at the metal chassis holes and see if it illuminates - even for a split second.

The LED string is wired in series - you can see this if you look at the back of the SMPS board @ Connector P801. The middle two pins are connected to each other.


Are you measuring the voltage from VLED+ to VLED-? Or referenced to ground? Given that you read +125V, my guess is that you have at least one open LED. Do you have an LED tester? Might be time to open up the panel and have a look for blown LEDs.

Do you get the proper voltages on the connector from the SMPS to the main board?

Yes that's the correct SMPS board that I have which you referenced.

So I originally thought I had a bad led or two and disassembled the tv to get to them. Testing each showed they all worked. I then found out that the mainboard was faulty at the microprocessor.

I found an exact replacement on eBay cheap which I purchased. Now with the new one I have different symptoms. No flashing led light, no light at all actually and the only voltages I measure now are the two 3.3v.

With my original mainboard I get all voltages 3.3v 3.3v 12v 12v and 24v. No backlight flicker at all with either mainboards. Possible I purchased a faulty mainboard?

In regards to testing LED voltages I measured referenced to chasis ground. Should I measure at led + and led - instead?