LG 50LN5400 Screen Flash Standby Go's Out

[coppercitycomputer]

Greetings I have a LG 50LN5400 that when plugged in gives a red stand by LED then when you hit the power button the screen flash's for just a micro sec then the LED fades/go's out, pushing the power button again with the LED off will make the screen flash then the LED will come back on and stay on. And sometime /other times the LED will do a slow fade like a start up fade, then the screen flash's then the led go's out!

Made in May of 2014. I have not gotten the back off yet, thought some of you might know right off hand or if it's a common problem! I will remove the back torrmow and get photos etc.

[coppercitycomputer]

Re: LG 50LN5400 Screen Flash Standby Go's Out

As promised here are some photos, the diodes appear to check out ok, I get infinite reading on the output of power supply to the screen LED's, R804 in the upper right side of the power supply is wide open, with LED's plugged in or not! Caps appear ok, I see northing that screams bad!

[Andrew F. Ali]

Re: LG 50LN5400 Screen Flash Standby Go's Out

When you say R804 is wide open do you mean if a resistance check is made you get no reading? I would pull one end off the board and check the resistance again. If 'open' I'd check both points on the board for short cct with respect to the chassis ground. If nothing show I'll replace the R804 with a 1.2ohm resistor first and give it a try.

[coppercitycomputer]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Yes wide open is 000 same as touching leads together, one leg of r263 r264 and read 1 and other read 0 (by the trans) R251-R253 all read 000 one leg and level off in the 900's on the other leg. R822 R804 both pinkish in color read open to ground on both sides. This is all done with my black probe on the screw holding the power supply, and red taking readings. Let me know if I still have to remove the one leg and test again!

[coppercitycomputer]

Re: LG 50LN5400 Screen Flash Standby Go's Out

If the power supply is bad, I am ok with replaceing the power supply as a whole.

[budm]

Re: LG 50LN5400 Screen Flash Standby Go's Out

"Yes wide open is 000 same as touching leads together" That does not make sense to me, when the probes of the meter are touch together, it will show <1 Ohm (000 Ohm as you indicated) so if the resistance between the two legs of the resistor show the same as the reading when the two probes of the meter touching together, then the resistor is not open.
R804 has Brown, Red, silver, gold = 0.12 Ohm
BTW, R804 is the resistor for the SOURCE pin of the power MOSFET Q801 which is for the boost converter circuit to produce the Voltage for driving the backlights LEDs. I doubt that the resistor is bad.
You will not get anything at the screen LED connector until you have BL-ON signal from the main board.
At this point you need to report the DCV of each pin of the connector of the power supply board that goes to the main board, you MUST provide the name of each pin also. Report the readings when TV is plugged in and when the power switch is activated.

[Lireb93]

Re: LG 50LN5400 Screen Flash Standby Go's Out

What was the end result? Did you find out the problem? I have one of the same TV's which had sound but no picture. Does everything as advertised, other than the picture (screen is black). Any suggestions or help of any kind would be greatly appreciated. Thanks in advance.

[coppercitycomputer]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Turns out the power supply is not at fault. A replacement did not fix the problem.

[jeffj7]

Re: LG 50LN5400 Screen Flash Standby Go's Out

these sets have a major problem with the led's failing. they short till one opens up. unless you only have one led bad your need to replace the whole set of led's

[budm]

Re: LG 50LN5400 Screen Flash Standby Go's Out

My post 6 "At this point you need to report the DCV of each pin of the connector of the power supply board that goes to the main board, you MUST provide the name of each pin also. Report the readings when TV is plugged in and when the power switch is activated."
If we know what the Voltages are at the connector that would have saved you from buying the power supply board.

[jimminoz]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Hey, I`ve got the same problem with the same model TV. Got the back cover off and looks easy enough to replace boards, but which one??? Seems Coppercitycomputer had no luck with the power board.
If it`s the LCD`s might as well chuck it out and get a new one. Date of manufacture is June 2013. Only 3 years old and had the bomb.
Apparently from searching around the internet this is becoming quite a common problem with this particular model TV. Would be good if someone has found a quick fix.
Might have to bring my old Hitachi plasma 46inch back into service. Bought it back in 2002 and still going strong.
Any advise would be appreciated.
Thanks.

Jim

[ReeceyBurger123]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Hey, I`ve got the same problem with the same model TV. Got the back cover off and looks easy enough to replace boards, but which one??? Seems Coppercitycomputer had no luck with the power board.
If it`s the LCD`s might as well chuck it out and get a new one. Date of manufacture is June 2013. Only 3 years old and had the bomb.
Apparently from searching around the internet this is becoming quite a common problem with this particular model TV. Would be good if someone has found a quick fix.
Might have to bring my old Hitachi plasma 46inch back into service. Bought it back in 2002 and still going strong.
Any advise would be appreciated.
Thanks.

Jim

Whats the fault first, I have a repair video coming for this Psu soon. Seems like common issue is cold solder joints on the transformer rivets.

[jimminoz]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Hi ReeceyBurger123.
The fault is screen flashes for a split second when turned on then goes out. When it flashes you can see the LG Logo. Seems the back-light and picture work ok for a nano second then it blacks out. Sound still works.
Some parts suppliers offer a full repair kit ( power board, main board and T-con board ) for around $100 but they warn that this particular model has Back light problems and the repair kit wont fix it.
Here is an extract from a consumer affairs complaints forum about a similar year and model number.
I]LG TV 55' Model: 50LN5700 - After 2.5 years my LG TV screen went black. When I turn on the TV I see a bright flash and LG logo and goes back to dark and can't see the screen. I am surprised to see that a lot of folks have experienced this exact issues after 2.5 years of purchasing the TV. This sounds me like this product need to be recalled and LG needs to respond to these claims as soon as possible or more investigation needs to be conducted.[/I]
This was somebody else s complaint from the USA. There were many more like it. I am in Australia so you can see it is a world wide common problem with this TV. It`s a bit rough when you pay good money for a TV and it only lasts 2-3 years.

Jim

[budm]

Re: LG 50LN5400 Screen Flash Standby Go's Out

I will not be surprised if it has bad LEDs.
Similar to your SET:
https://www.badcaps.net/forum/showth...ht=LG+47LN5790
LG drives the LED at full spec. which in its own LG LED spec is said not to run the LED at full spec.

https://www.youtube.com/watch?v=Bf5T2wwtydY

[R_J]

Re: LG 50LN5400 Screen Flash Standby Go's Out

I know someone that has the same model 50LN5750-UH, It had an open LED in the panel.

[johns1mj]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Just confirming same model, same symptoms, bad led. I used a model train transformer to supply voltage to each strip. I had a r2 with a bad led.

[jhuncruz2007]

Re: LG 50LN5400 Screen Flash Standby Go's Out

Check the led backlight , its always ther culprit in those models.