LG 50PM680 No picture, sound working

[Tom3dJay]

Hello guys, I'm new to your forum, but I've done some extensive reading already.
I'll cut straight do the point here:

My set gives me no picture, sound is working, but If I remove upper buffer completely, I'll get picture on the lower half of the screen.
Part number for the upper buffer is EAX64300101, it's used in other LG plasma sets too.
There's only one visible problem with the top buffer: IC chips got slight "dark" mark in the corner, but it doesn't smell burned at all and I've seen couple boards online with this type of darker corner, so I don't really know.

What do you guys think? It's it sole upper buffer failure or is the panel dead?

(everything else seems to be in order, no bad caps or fuses)

[MagicSmoke]

Re: LG 50PM680 No picture, sound working

Watch this video to test your buffer. The chips can fail with no visible damage.

https://www.youtube.com/watch?v=51SZ...Y&noredirect=1

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

Watch this video to test your buffer. The chips can fail with no visible damage.

https://www.youtube.com/watch?v=51SZ...Y&noredirect=1

Thanks for swift reply. Definitely a good vid, but I'll have to borrow the multimeter later, since don't have one.

What if the buffer tests okay?

This is one of LG series sets with razor thin edge, potentially suffering from ribbon damage due to design flaw.

[tom66]

Re: LG 50PM680 No picture, sound working

There is a good possibility that the Y-scan ribbon is damaged, which is fatal to the panel. But, usually only happens on the top most chip.

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

Thanks a lot boys, I'll get back to you once I check for short on the upper buffer.

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

Small update:

I measured the resistance on the upper buffer, and found out that only couple pins give me any good reading, so I guess ICs are dead.

Another problem is, the lower part of the picture stopped working too. I suspect it may be some mistake on my part when I was trying to unplug the y-sus (while powered off). Possibly even mechanical damage, but I couldn't find anything wrong.

It's really difficult to get the lower buffer unplugged, so I measured it while still plugged to ribbons panel and y-sus and seems like everything is now dead on the lower board too, resistance shows "1" no matter what ohm scale I choose on the multi meter.

Y-sus is still buzzing, gives good "switching on" sound so I don't suspect it being dead, I checked the ribbons too, and the seem to be alright.

How would you proceed? Thanks in advance for any suggestions, you guys are awesome.

[tom66]

Re: LG 50PM680 No picture, sound working

The pins should normally appear open - the internal structure is a MOSFET with an antiparallel diode. A low resistance reading in both directions is bad.

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

Alright, that makes sense actually, the upper gives me close to zero both ways on couple pins.

This is the resistance on the lower buffer. Upper gives me half of that on all pins, except for couple pins on top, which gives zero both was.

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

Hey, guys, small update, I just bought y sus and both buffer boards!

Unfortunately, this didn't fix the problem completely.

Now I'm getting very quick picture blink accompanied with the with classical switch and buzz sound, but buzzing sound goes away at the same time that picture does.

Any idea what's wrong?

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

bump

The led light on main board gives long-short -- long-short signal.

[ned1]

Re: LG 50PM680 No picture, sound working

you had bad upper buffer. If you removed upper buffer and got picture on lower screen then that was all you need to change. Put back your old y-systain and lower buffer and install new buffer. Make sure your new buffer is not short.

[Tom3dJay]

Re: LG 50PM680 No picture, sound working

you had bad upper buffer. If you removed upper buffer and got picture on lower screen then that was all you need to change. Put back your old y-systain and lower buffer and install new buffer. Make sure your new buffer is not short.

Oh, I think I forgot to update the thread, but picture went gone shortly after.

I'm not really sure what caused it, perhaps bad handling of components or maybe some type of short while measuring, no clue.

That's why I bought some buffers and y-sus.