LG 50PA650T Plasma- Help required :)

[George266]

Hi all. I have got LG 50PA650T Plasma TV , but i am somehow stuck
.
The plasma does turn on (relay click) but turns OFF after about 4 seconds ( another relay click) . I ca hear Y-Sus board buzzing but NO image at all , JUST audio. Then I have disconnected both buffers and the result was exactly same.
Voltages:
VS 1.1V
VA 3.4V
M5V 5.2V

Just to make sure the power supply is okay I have unplugged the Ysus and connected 100W bulb into VS output a the bulb did light up bright.
So I said, Okay bad Ysus and went on EBay and bought one.

I have installed the new Ysus and plugged ALL connectors into it. Same result, no picture-just Buzz and audio (..money for new ysus wasted?)

SOME MORE MEASUREMENTS- Ysus disconnected :
VS 205V
VA 52-55V (fluctuate)
M5V 5.18V
M-on 3.30V
RL-ON 2.53V
STB 5.23V /3.47V when OFF
5.2 5.2V
Err Detect 0.6V
Input board red LED- ON (off when Ysyus plugged in)
Controll board green LED flash sequence : medium-medium-long-short (off when Ysus plugged in)
No bulged capacitors, oll fuses OK.

Anyone can help what should I check next?
Note: I am not professional I am just trying to learn because I just like to fix things-and reuse them.

[tom66]

Re: LG 50PA650T Plasma- Help required

Loud buzz? Too loud for actual watching?
Check panel for chips, cracks and other damage.
https://www.youtube.com/watch?v=-iAm...s&noredirect=1

[George266]

Re: LG 50PA650T Plasma- Help required

Thanks Tom. The Buzz is not as loud as the one on the video -but in quiet room with volume muted it would be noticeable if not annoying. Thing is, the ysus makes buzzing noise even when the buffers are disconnected.. But I will check the screen for cracks too

[tom66]

Re: LG 50PA650T Plasma- Help required

Try with just one buffer at a time.
If it works with the top out, you most likely have a bad plasma panel due to an LG design flaw. The plastic frame around the TV eats into the ribbons, which damages the buffer board. I had exactly the same model, couldn't fix it.

[George266]

Re: LG 50PA650T Plasma- Help required

I have just checked the panel, there are no cracks. Just wondering is there any way to check if the Ysus is okay?
Just thinking -could bad buffer damage the newly installed Ysus?

But as you said- it could be the ribbon cable. I have read your your post where you have mentioned it . Actually, the VS voltage is nearly 0V with ysus connected , buffers disconnected -therefore bad Plasma panel shouldn't affect it as there is no connection between ysus and panel ?

[tom66]

Re: LG 50PA650T Plasma- Help required

Ah - missed that. 0V on Vs with Y-sus in? That's a dead Y-sus there... Try checking it for shorts & then order another one... I bet the seller never tested it.

[George266]

Re: LG 50PA650T Plasma- Help required

Which components on Ysus do you usually check for shorts Tom ?

[tom66]

Re: LG 50PA650T Plasma- Help required

Any of the devices mounted on the heatsinks.

[George266]

Re: LG 50PA650T Plasma- Help required

Hi all,
Now after I have replaced the YSUS the second time (after the first seller from Ebay send me a faulty one) and I am finally getting the right voltage on the resistors VY=189.3 VSC=159.6

Hoverer, when I plug the bottom buffer into the YSUS -->the both VY and VSC voltages drops to nearly 0V .The results are same when I unplug the ribbons which are going to the panel .
Voltages are fine when only the top buffer is connected.

This leads me into conclusion that the bottom buffer is shorted. Now after I have been reading tom's66 comments about ''The frame around the TV eats into the ribbons'' design flaw, I have tested the ribbons for short against the frame and i didn't find any shorts.
Is there anything else I should test before ordering a new buffer -->and maybe ending up with unfixable Plasma which has the ''eaten ribbon issue'' ?

Also do you normally replace both buffers even if the top one isn't shorting the YSUS?

[tom66]

Re: LG 50PA650T Plasma- Help required

Unfortunately I was slightly wrong there - the frame eats into the ribbons causing open circuits not shorts.
However, the ultimate failure is the same - bad buffer board, dead panel.
You need to inspect the ribbons carefully, the hole/break can be almost invisible.

[George266]

Re: LG 50PA650T Plasma- Help required

I have just disassembled the panel and I have found some suspicious damage. Here are the pictures:

[George266]

Re: LG 50PA650T Plasma- Help required

[George266]

Re: LG 50PA650T Plasma- Help required

[George266]

Re: LG 50PA650T Plasma- Help required

It is hard to get really close image with standard camera but actual top plastic layer is broken and the conductive part of the ribbon is exposed. The only thing which baffles me is:
1.) why the bottom buffer died when the damaged ribbon is connected to the top one..
2.) Why I am not getting image at least on part of the screen?

Any Ideas?

[tom66]

Re: LG 50PA650T Plasma- Help required

Exactly the same I had. I'll upload a picture shortly.

[tom66]

Re: LG 50PA650T Plasma- Help required

I think you will find ribbon defect lines up with the screw mounts or plastic nibs. They seem to eat into the ribbons on these.

That must be 5th LG 2012 series 50" FHD with this problem. (50PA5500, 50PA650T, 50PM670T)

[George266]

Re: LG 50PA650T Plasma- Help required

It is very difficult to actually see if the conductive part broken, even if I put LED torch behind the ribbon i Can't actually see the breakage. The conductive part is definitely exposed as the top layer bubbled and rubbed through. I believe this happen when you grab and squeeze the screen by palms when moving etc..
I am still tempted to get a new buffer as I can't see the conductivity breakage yet ..
Eeehm , will have to think about if is it worth the risku buying the part.

Tom , if you still have the panel disassembled would you be possible to test it with torch light to see if the snapped lines are visible?

[tom66]

Re: LG 50PA650T Plasma- Help required

I have since gotten rid of this TV unfortunately. Simply bending the ribbon back showed the break easily.

[thuss]

Re: LG 50PA650T Plasma- Help required

Hi

Could do with some advice. I'm trying to repair my mates lg 50PM670T (which I believe Tom66 you mentioned has a panel design fault). We removed the top buffer tv did not come on.We removed the bottom buffer and we got some activity in the top section and the vy voltages etc came back. So he ordered a bottom replacement buffer board.

We replaced the bottom buffer board the tv came on however theres a 2mm black horizontal line between the two bottom buffer chips. We switched tv off and tried to reseat the ribbon several times but the line would not go.
Eventually we were back at square one ie with no image. I think its a bad panel but could it be a bad buffer I cant see any damage to the panel ribbons.

Any help would be appreciated