LG 50PS11 plasma -top half of screen darker

[braxton]

I received this tv for cheap because owner said it would not power on. I brought it home, plugged it in and it powers on fine. However the top half (exactly half) of the screen is darker and has thin horizontal black lines. I've attached a picture.

Is this likely a cable connection issue or something else??

[chrismurphy]

Re: LG 50PS11 plasma -top half of screen darker

I was suspecting buffer boards if the screen was divided in half , but from the photo it looks more like 2/3 so i suspect the x sustain board connections to the panel or the board itself
As the video image seems ok, i would go for the x sus as the possible culprit , re seat all connections and look for dry joints on that board especially high current inductor coils connections

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

I was suspecting buffer boards if the screen was divided in half , but from the photo it looks more like 2/3 so i suspect the x sustain board connections to the panel or the board itself
As the video image seems ok, i would go for the x sus as the possible culprit , re seat all connections and look for dry joints on that board especially high current inductor coils connections

The picture is misleading because there is a bottom black bar that is part of the screen. So in reality, exactly half of the screen (top) has interspersed black lines, suggesting the upper buffer board is likely faulty. This board (part number EBR61831601 ) seems to be hard to find, so I'm wondering if it is repairable??

[tw2005]

Re: LG 50PS11 plasma -top half of screen darker

I'm thinking buffer board. I actually replaced a lower board on a Pk350 and the lower board produced a slightly darker image to the top

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

I tried reflowing the upper buffer board in an oven at 385 for 10 minutes.
No change.

[Alastair E]

Re: LG 50PS11 plasma -top half of screen darker

Its the Y-SUS.

--There's an Octal Buffer-chip on the Y that goes faulty--C541 rings a bell. However--Theres about 5 of these chips on the board and I have no idea which one it is. You would need a scope to trace out the signals into and out of each one--or just replace 'em all.

Its the serial-data supply from the control-board through the Y to the screen Buffer-board that becomes corrupted. Either the Even or the Odd data is missing for the upper board...

[ReeceyBurger123]

Re: LG 50PS11 plasma -top half of screen darker

Its the Y-SUS.

--There's an Octal Buffer-chip on the Y that goes faulty--C541 rings a bell. However--Theres about 5 of these chips on the board and I have no idea which one it is. You would need a scope to trace out the signals into and out of each one--or just replace 'em all.

Its the serial-data supply from the control-board through the Y to the screen Buffer-board that becomes corrupted. Either the Even or the Odd data is missing for the upper board...

+1 also seen this before.

[Alastair E]

Re: LG 50PS11 plasma -top half of screen darker

Ive seen it twice now. Once where the top half of picture was intermittent and another where every other line was missing,--just as above--the height of the affected picture randomly bouncing up and down.

I just bunged another Y in it. Cured the problem, couldn't be bothered to trace the chip--I had a spare board...

[tw2005]

Re: LG 50PS11 plasma -top half of screen darker

Ha, should have zoomed in for a closer look, I see what you blokes mean with the lines. With the LG I had there were no lines.

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

Crap. I already ordered a $50 buffer board based on suggestions and other threads...

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

Just an update with some good news and some bad news.

The upper buffer board arrived today. Upon installation, the tv worked perfectly and the upper part of the screen was back to normal. The bad news is it worked for 3 hours or so and then the picture went out but I still had sound. Restarts didn't help. I then unplugged the tv and left it for an hour or so and pulled the back cover back off to have another look. I then powered on the set and the picture came back for a bit and then went out again after a few minutes.

Recall that when I bought the tv, the previous owner said it would power on but nothing would show on the screen. When I brought it home and plugged it in, it powered up fine but had the top half of the image was darker. This seems to suggest that I have a "sporadic" issue with loss of picture. To me this usually means a cold solder joint (or bad caps but the electrolytics visually seem fine), but where should I start looking? Could there be something else that could cause the picture loss to come and go??

[tw2005]

Re: LG 50PS11 plasma -top half of screen darker

Sounds like could be cracked soldering somewhere on the ysus if it came good disturbing that board.

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

I plan to take out the psu, y-sus and z-sus boards and check for cracked solder joints and resolder if necessary.
If that doesn't help, maybe I will reflow main board, control board and buffer boards in oven...

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

The p/s, z-sus and y-sus boards do not seem to have any questionable solder joints that I can see. Next I am about to bake the main video/audio board and logic board together in an oven at 385F for 10 mins.
However, I noticed there are quite a few cylindrical silver caps on the boards- see attached picture. Do I risk damaging these caps by baking in an oven?

[tw2005]

Re: LG 50PS11 plasma -top half of screen darker

Sounds risky. Have you tried even just tapping or flexing the ysus? On most lg you can isolate the main. Jumper the logic bd for the test patterns. I'd be inclined to work around the ysus. May be a bad ic

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

Thanks,

The set seems to work perfectly some of the time; that is the strange part.
It would suggest that a component hasn't failed completely at least...

I will try tapping and flexing more and see what happens.

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

would like to do an auto test pattern to determine if main board is a problem.
I've attached a pic of the auto-gen area on the board with 4 pins.

Which pins do I jumper?

[Electronic Handyman]

Re: LG 50PS11 plasma -top half of screen darker

Many times in such cases when a set is acting up then is moved etc and acts differently I find bad soldering connections or a loose connector or even bad connections on the plug in soldered connectors.I'd re-solder all the hot spots like parts connected to or close by the heat sinks, any coils on the y-sustain board especially the two red coils and the big capacitors connections.Check those caps carefully bec they are known to fail too.

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

Many times in such cases when a set is acting up then is moved etc and acts differently I find bad soldering connections or a loose connector or even bad connections on the plug in soldered connectors.I'd re-solder all the hot spots like parts connected to or close by the heat sinks, any coils on the y-sustain board especially the two red coils and the big capacitors connections.Check those caps carefully bec they are known to fail too.

Thanks. That is what I suspect too as lifting and moving the tv seems to influence whether it works or not. I have checked carefully for solder cracks but don't see any so far. Will need to keep checking...

[braxton]

Re: LG 50PS11 plasma -top half of screen darker

Many times in such cases when a set is acting up then is moved etc and acts differently I find bad soldering connections or a loose connector or even bad connections on the plug in soldered connectors.I'd re-solder all the hot spots like parts connected to or close by the heat sinks, any coils on the y-sustain board especially the two red coils and the big capacitors connections.Check those caps carefully bec they are known to fail too.

Further to this point, most of the boards are well supported on the frame and are quite sturdy when bolted down. The exception is the main video/audio board, which can flex quite a bit. That board is my "main" suspect now, which is why I would like to figure out how to activate the bypass test patterns- (see post #17 above with 4 prong test point that I'm trying to figure out what to jumper).