LG LCD 42LG50-UG has sound but no picture

[jortor]

I read a previuos tfread where someone had a similar problem with a "plasma". I am having this issue with a "LCD". tv is 3 years old, of coarse out of warranty. any help will be greatly appreciated.

[technomaniac]

Jortor, A good first step would be to see whether you do not have a picture, or you just can't SEE it. If you get a bright torch and shine it on to the LCD display, you might be able to see movement on the screen. If you DO see movement, then your LCD panel is working, and is being fed a picture. It's just that the fluorescent lights or LEDs behind the display are not working for some reason. On the other hand, if you cannot see any movement, then the LCD panel may be faulty or it is not being driven.

[GT250]

Welcome to Austech jortor.

You have to give more background information for us to help you.

Do you have any blinking lights?
Was there any noise when it blank?
Was it working fine and then went blank as you were watching it?
Was it blank one day when you turned on?
Has it ever gone blank before - but came good for a while?
If you change channel does the sound change accordingly?

As the previous has mentioned, have you turned off all the lights and seen if there is any glow at all?

[TVguy]

tv is 3 years old, of coarse out of warranty

Are you aware that this series of LCD TVs carried a 3 Year warranty? Take the easy path and contact LG.

[jortor]

--------------------------------------------------------------------------in reply to previous request for more info.
Welcome to Austech jortor.

You have to give more background information for us to help you.

Do you have any blinking lights?........................................... ..........NO
Was there any noise when it blank?............................................ ....NO
Was it working fine and then went blank as you were watching it?.......YES
Was it blank one day when you turned on?.......................................NO
Has it ever gone blank before - but came good for a while?.................YES
If you change channel does the sound change accordingly?.................YES

I was in comtact with lg, and very politely they told me I was on my own.

[mickstv]

You'll need to get a service manual from somewhere as you need to work out whether one of the screen inverter boards are faulty or the power and control lines are faulty from one of the other boards. Some of the LG's will have the edge connectors marked with the voltages and what function they do. You mich be looking for say 24 volts most likely for the inverter boards power and your inverter on/off wiring might be 3.3v or 5v when unit is turned on.

I couldn't find the UG version listed on the LG Aust service site which tells me your not local ?




WARNING WARNING WARNING

Messing with LCD's and PLASMA's can be dangerous lots of HiVoltage which could Kill so be very careful. So If you don't reguarly work on electronics I suggest you take it to someone that is fully qualified.



Mickstv

[GT250]

Hi Jortor,
So where are you then? Hunting around the world for a solution?
Well here in OZ we try and be helpful.

Anyway, if your set does this;

Has it ever gone blank before - but came good for a while?.................YES

Then it is likely to be a component heating up and breaking contact.

As you don't seem to have a picture now, it might have finally 'opened up' so as not to make contact.

As Mickstv has said poking around these thimgs can be VERY bad!!!

I had a Plasma that when i pressed on a main chip, the picture was fine. Take my finger off and it went bad. Putting a fan on the chip all was ok... But who wants a fan running all the time with the back case off to watch tv?

So look. Take it to a repair shop. Telling them that it goes blank and then goes good, then comes back on again, will give them the hint that it 'might' be a solder joint that breaks when warmed up [They are very common].

Use the words "So you think it might be a dry joint..."? Look confident, as though you know what you are talking about
Google 'Dry joint", before going ahead with this

If they know, that you know, what they know, and that you might know what they don't want you you to know, then at least you knew what they didn't want you to know...

So don't go poking your fingers around the back of the TV! It's not worth money to risk getting 40,000volts.

Most of the posters here have had years of experience.

New plasma's and such are only $500 to buy.

Get a free quote from people that know what they are doing.
No harm done, and basically the LG range from those days was rubbish anyway.

[TVguy]

I couldn't find the UG version listed on the LG Aust service site which tells me your not local ?




WARNING WARNING WARNING

Messing with LCD's and PLASMA's can be dangerous lots of HiVoltage which could Kill so be very careful. So If you don't reguarly work on electronics I suggest you take it to someone that is fully qualified.



Mickstv

Well done Mickstv I didn't notice the UG suffix, therefore not an AUS product. I quite agree, self repair without knowledge is fraught with danger!

[iwacelect]

Hi Jortor,
So where are you then? Hunting around the world for a solution?
Well here in OZ we try and be helpful.

Anyway, if your set does this;

Has it ever gone blank before - but came good for a while?.................YES

Then it is likely to be a component heating up and breaking contact.

As you don't seem to have a picture now, it might have finally 'opened up' so as not to make contact.

As Mickstv has said poking around these thimgs can be VERY bad!!!

I had a Plasma that when i pressed on a main chip, the picture was fine. Take my finger off and it went bad. Putting a fan on the chip all was ok... But who wants a fan running all the time with the back case off to watch tv?

So look. Take it to a repair shop. Telling them that it goes blank and then goes good, then comes back on again, will give them the hint that it 'might' be a solder joint that breaks when warmed up [They are very common].

Use the words "So you think it might be a dry joint..."? Look confident, as though you know what you are talking about
Google 'Dry joint", before going ahead with this

If they know, that you know, what they know, and that you might know what they don't want you you to know, then at least you knew what they didn't want you to know...

So don't go poking your fingers around the back of the TV! It's not worth money to risk getting 40,000volts.

Most of the posters here have had years of experience.

New plasma's and such are only $500 to buy.

Get a free quote from people that know what they are doing.
No harm done, and basically the LG range from those days was rubbish anyway.

yeah leave it us "experts" we've done all the...

"..well i was just going to measure this and the probe slipped.... that was 3 hours ago and now the thing still doesn't go...F**k"...

or

just leaning in to measure the power supply and leant on this metal bit with my finger, just to steady my probe (dont want the same thing happening to this unit) and...

bang...

when i woke on the otherside of the room, head pounding and cold profuse sweating and wondering why glasses are 15" away sitting on the lounge suddenly realised the HEATSINK i just used to steady my finger was in the power factor correction circuit and was at 400v + at mains....

yeah we experts have learnt over time, (all you older guys read "first hurtfull expeirence with a tripler at hv") and yes even mean the K9-2BS philips chassis now thats learning what hv can cause

be smart get someone else to look at it.

as your in another country, it's highly unlikely it'll be me, hooray!

[mickstv]

yeah leave it us "experts" we've done all the...

"..well i was just going to measure this and the probe slipped.... that was 3 hours ago and now the thing still doesn't go...F**k"...

or

just leaning in to measure the power supply and leant on this metal bit with my finger, just to steady my probe (dont want the same thing happening to this unit) and...

bang...

when i woke on the otherside of the room, head pounding and cold profuse sweating and wondering why glasses are 15" away sitting on the lounge suddenly realised the HEATSINK i just used to steady my finger was in the power factor correction circuit and was at 400v + at mains....

yeah we experts have learnt over time, (all you older guys read "first hurtfull expeirence with a tripler at hv") and yes even mean the K9-2BS philips chassis now thats learning what hv can cause

be smart get someone else to look at it.

as your in another country, it's highly unlikely it'll be me, hooray!

Yeah I had an old Sanyo give be a fair old shock once, Boss always used to say keep one hand behind your back when working on TV's.

I have never experienced a HV zap/burn as such, I have heard it hurts for weeks.



Mickstv

[iwacelect]

Yeah I had an old Sanyo give be a fair old shock once, Boss always used to say keep one hand behind your back when working on TV's.

I have never experienced a HV zap/burn as such, I have heard it hurts for weeks.



Mickstv

our apprentice found out and he never worked on CRT's...

for a while there we mucked around with designing solid state driven tesla coils, (only made possible with IGBT's at the time) such as the one we let the apprentice take to tafe for demonstration purposes...

but teens being the way they are... (sorry the videos sideways, wasn't the camera man)

[ame=http://www.youtube.com/watch?v=k0ZD_GfvKCw]YouTube - caleb gets zapped from tesla coil[/ame]

it took weeks for the hole to heel!!!!

[mickstv]

our apprentice found out and he never worked on CRT's...

for a while there we mucked around with designing solid state driven tesla coils, (only made possible with IGBT's at the time) such as the one we let the apprentice take to tafe for demonstration purposes...

but teens being the way they are... (sorry the videos sideways, wasn't the camera man)



it took weeks for the hole to heel!!!!

Hmmmm he seemed pretty happy with what happened. But it's a good way to show what might and can happen.



Mickstv

[iwacelect]

the flouro tubes for effect.

he was never told to wave a screwdriver at the top, thats all his own idea!

[Oscar]

Good honest call IWAC .Yep ive copped heeps of zaps and dual repairs due to the slipped probe.I think anyone in the trade has.Thank god we are still alive even if struggling to make ends meet.

[jortor]

v

[jortor]

i HAVE A 42 INCH, 3 YEAR OLD, LCD TV (JUST OUT OF WARRANTY) THAT HAS LOST PICTURE, SOUND WORK FINE. ANY HELP WILL BE GREATLY APPRECIATED.
THANKS
LG LCD
MODEL: 42LG50 -UG

"problem fixed"
I went looking inside tv (since it was out of warranty anyway) checked all wire harness, unpluged them, then repluged them, turn power back on and it started working again, must have been a loose cable.(I think), anyway it is working now. I wanna thank those who responded to my post.

[aztimmay]

Jortor, A good first step would be to see whether you do not have a picture, or you just can't SEE it. If you get a bright torch and shine it on to the LCD display, you might be able to see movement on the screen. If you DO see movement, then your LCD panel is working, and is being fed a picture. It's just that the fluorescent lights or LEDs behind the display are not working for some reason. On the other hand, if you cannot see any movement, then the LCD panel may be faulty or it is not being driven.

Hey so I came across this thread and did this, found that if I turn off the lights and put a flashlight next to it i can see the snow on the channel it's on. I pulled off the back and looked for the fuses, but i can't tell if either fuse is blown or anything because it's not made of glass (it's white). So I was disconnecting the cables and connecting them again, but it didn't make a difference for me. So if I am seeing some kind of picture with the lights off and the flashlight held next to it, what is that? The back lighting or something else?