LG Plasma 50PG30 bottom half screen darker than top half

[Sevenqi]

LG Plasma 50PG30 bottom half screen is darker than top half, please see picture, first time see this problem, not sure if y lower buffer board or z-sustain board problem.
The z board(EBR41733201) looks like has two sections, not sure if one section handle upper and one handle lower

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

My initial thoughts would be lower buffer

[Sevenqi]

Re: LG Plasma 50PG30 bottom half screen darker than top half

I observed the bottom screen again carefully, it looks like darker, but the pixel seems interlaced scanning, see pictures. The lower buffer board has 3 headsinks and 6 connectors to the screen, all the ics have the same problem? Is the lower y buffer board bad?

[capkid]

Re: LG Plasma 50PG30 bottom half screen darker than top half

My initial thoughts would be lower buffer

Yeah, that looks like a lower Y-buffer on its way out.

[tom66]

Re: LG Plasma 50PG30 bottom half screen darker than top half

No, to me it looks like the ODD/EVEN control is not reaching the buffer board. Consider one of the little logic level buffer ICs (not the buffer chips, the inverters) or something on the Y-sus. Compare the difference in buffer control signals between the top and bottom. The output buffers which drive the panel are simply shift registers with a latch control.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

I found this thread although it's does not have the answer but this one was intermittent so has me wondering if maybe a bad joint or connection somewhere?

You'll have to scroll down to #952

http://www.avforums.com/forums/plasm...thread-32.html

[tom66]

Re: LG Plasma 50PG30 bottom half screen darker than top half

If it's intermittent, then it could be a problem with a connector, but it seems very strange that it would only affect odd/even rather than clock, data, output enable, clear etc.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

If it's intermittent, then it could be a problem with a connector, but it seems very strange that it would only affect odd/even rather than clock, data, output enable, clear etc.

No idea, the updated photos to me seemed every second line was missing very similar to incorrected seated ribbons but for me something to do with either the whole buffer board or as you've alluded to what coming from the ysus.

I guess if I was faced with this I'd reseat the ysus/buffer connector and then maybe check out the connectors just in case a fracture was there, maybe even some gentl flexing of the boards or connectors see if any change.

Interesting fault

[tom66]

Re: LG Plasma 50PG30 bottom half screen darker than top half

What would be useful to determine would be if it affects odd rows or even rows, this could be tested using lots of horizontal lines, if the panel has pixel shifter turned off and 1:1 scan enabled.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

If it's intermittent, then it could be a problem with a connector, but it seems very strange that it would only affect odd/even rather than clock, data, output enable, clear etc.

Working with your theory, on the odd and even data . Looking at the bottom buffer board one connector handles ODD, the other EVEN.

If one of those was poorly seated would that make sense for what we see ? I have no idea so I'm just throwing out random thoughts here

[tom66]

Re: LG Plasma 50PG30 bottom half screen darker than top half

Would make sense. Looks like we've got a STROBE, CLOCK and two output controls.

I wonder why there are two output controls?

It also looks like there's separate addressing (VSC) and 5V supplies for odd and even drives.

The VSC is used to select each row and the 5V powers the buffer chip's level shift logic, which is usually floating and relative to the SUS output, same as Panny plasmas, perhaps bad 5V regulator IC as seen before?

Not sure what VPP is for though!

Wish I could see under the buffer board, it looks like they provide separate sustaining for odd and even ICs, very strange.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

I think this is the matching ysus

[tom66]

Re: LG Plasma 50PG30 bottom half screen darker than top half

Quite an old LG, probably one of their first 1080p 50".
Looks like they do separate the odd and even sustain outputs.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

It does look like 2008 date stamps.

[tw2005]

Re: LG Plasma 50PG30 bottom half screen darker than top half

Is this the part of the circuit you were thinking?

[Sevenqi]

Re: LG Plasma 50PG30 bottom half screen darker than top half

I reseated the two connectors BTW the y board and the lower buffer, and 6 connectors BTW the lower Buffer and the panel, but no change. I touched the heatsinks, the lower board and upper board looked similiar, and the y-board too.
I attached the y board and the P/N.
This TV's manufactoring date: January 2009.

[Sevenqi]

Re: LG Plasma 50PG30 bottom half screen darker than top half

Final update: I replaced the lower buffer, TV works perfect.

[Rotyb]

Re: LG Plasma 50PG30 bottom half screen darker than top half

Can you refer me to the buffer you replaced? I have same problem. Thank you