LG 50PK790 No Image No Sound

[RavenHerald]

Hello,

I'm having problems with my LG 50PK790 plasma tv. When it is turned on the standby light goes off and the usual click it makes when turning on occur as normal, but the screen is grey and there is no sound.

I can't currently get a clear photo of the back of the tv as I can't move it by myself, but I can try and get photos of any specific components if needed.

Not sure if it is related, but I got the tv second hand as it had two single green lines running vertically down the screen. They didn't show if the image colours were dark if watching tv and didn't show up at all when running my PS4. It has been like that for months, maybe even a year and still worked fine.

Many thanks.

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

Have you read other threads about this set ? Common issue is the mainboard failing. Try running the test patterns.

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Hello and thanks for the reply.

I did search and thought it was likely the main board, but I didn't understand how to run the test patterns, are you able to explain? Thank you.

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Sorry photo is a bit fuzzy but hopefully okay enough for guidance, I know I need to disconnect a cable and then link two pins together but I'm not sure what any of those parts are on the board.

Apologies for asking for basic steps, all help is much appreciated.

[charis]

Re: LG 50PK790 No Image No Sound

if you have sound and not image is the Y SUS the IGBT dont have corect voltage and flex cables dont make good contact.If no sound also the main problem.

If your picture is corrupt or washed colors change the caps on Y & Z sustain boards calibrate the voltages VA VS.
If start and shutdown after 10 minutes or more is your power supply.
For the other set they start putting red or green dots and with time the problem get bigger but sometimes for example if you use a dvd input stop or if the unit get warm.
Its overload of the phosphorus a panel problem.

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

if you have sound and not image is the Y SUS the IGBT dont have corect voltage and flex cables dont make good contact.If no sound also the main problem.

If your picture is corrupt or washed colors change the caps on Y & Z sustain boards calibrate the voltages VA VS.
If start and shutdown after 10 minutes or more is your power supply.
For the other set they start putting red or green dots and with time the problem get bigger but sometimes for example if you use a dvd input stop or if the unit get warm.
Its overload of the phosphorus a panel problem.

Tbh non of that is true, thats just a concept. You need to diagnose before making statements.

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

Have you an image of the controller board please ?

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Imaged attached, thank you.

[Alastair E]

Re: LG 50PK790 No Image No Sound

if you have sound and not image is the Y SUS the IGBT dont have corect voltage and flex cables dont make good contact.If no sound also the main problem.

If your picture is corrupt or washed colors change the caps on Y & Z sustain boards calibrate the voltages VA VS.
If start and shutdown after 10 minutes or more is your power supply.
For the other set they start putting red or green dots and with time the problem get bigger but sometimes for example if you use a dvd input stop or if the unit get warm.
Its overload of the phosphorus a panel problem.

Ignore all the contents of this quoted post--Its ALL Utter Garbage!

Link the test-points 'Test-auto-gen' on control-board and retest

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

Ignore all the contents of this quoted post--Its ALL Utter Garbage!

Link the test-points 'Test-auto-gen' on control-board and retest

+100000 got to laugh at the phosphors being overloaded part though haha

[Alastair E]

Re: LG 50PK790 No Image No Sound

Aye--But my post wasn't much better--Cant see auto-gen on cont-board at all!

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

I think its on the unused connector block Ali

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Thank you, I was ignoring that but good to know I was right!

I got it connected, test patterns working fine.

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

Haha yep total trash talk never heard anything like it in my life, sorry to be a pain what pins were they can you upload an image ? Also that means your mobo is faulty

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Image is attached, should be clear enough so you can read anything you need off it but let me know if not. I left the wire in so you can clearly see where the points are {bottom right}, I realised the angle of the other photo hid them a bit!

Thank you both for all of your help in diagnosing, I really appreciate it. Unfortunately it seems to be hard to find a replacement for this model so I may have to bid it farewell.

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

I would offer to buy it if you consider selling it ? Dont trash it though you can fix it !

[RavenHerald]

Re: LG 50PK790 No Image No Sound

Sorry photo got squished smaller than I thought, have attached a close up.

Fixable would be awesome! It's a great tv and I hate getting rid of anything that could be fixed, how would I go about fixing it?

[ReeceyBurger123]

Re: LG 50PK790 No Image No Sound

Do you know much about Bga solder failing ? If so common fault is the solder under the Cpu on these boards going, try giving it a reflow if not best to replace it and heatsink or even fan cool the mb they get hot which is the reason for failures.

[RavenHerald]

Re: LG 50PK790 No Image No Sound

I hadn't even considered that it would be the solder, just presumed it would be one of the components! Thank you I will see if I can get it working, otherwise will be in touch if you did want to take it.

[charis]

Re: LG 50PK790 No Image No Sound

You are trash!
i try to talk simple all this gas inside a plasma is acting like a Phosphore.
In the instustry is a common language from the past every technician know this.
I do this for a living if you guys thinks you smart i said all the common problems on lg plasma in the above post.