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Flickering green dots on dark areas of pic, Samsung 50" plasma


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#1 of 10 OFFLINE   Phil Carter

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Posted May 04 2010 - 10:10 AM

Hi folks.

I have a Samsung PN50A550 plasma TV, 50", 1080p, which has begun exhibiting some unpleasant picture issues. In dark areas on the picture (near-blacks and dark browns especially) I can see flickering green dots, places on the screen where a single pixel changes from its dark color to green and then reverts. In some areas there is a positive swarm of these green dots. They continue to flicker and change even on a completely static image (for example, a paused Blu-Ray or DVD). Brightly-colored areas (yellows, pinks, blues, whites) do not show these dots and stay unchanged.

The TV is still under performance contract from the place I bought it, so they sent out a third-party technician to look at it. He adjusted "the voltage on one of the boards" on the TV and the dots were reduced (previously there were so many they were visible from six feet away), but have not gone away. I showed him that the dots were still flickering and changing even on a static image and he shrugged and said that was "normal" for this kind of TV.

Now, I'd always thought that on a completely static image there should be NO change at all in the color of a given pixel. The fact that I am still seeing movement, changing pixels, on an image which isn't changing, seems to indicate to me that there's still some kind of problem with the display. Am I right in thinking this?

Both my video sources are run directly to the TV, not passed through a receiver. The PS3 is connected via HDMI, and my PS2 (for old games, also plays DVDs in a pinch) is connected via component video. The issue is apparent on both sources (I used a scene from the Blu-Ray of Toy Story 2 on the PS3, then looked at the same scene on the DVD on the PS2). I also tried replacing the HDMI cable for the PS3 with no change.

I viewed the same scene on my girlfriend's 720p LCD television. There are no pixel changes at all on that image when it is paused.

I'm thinking the tech may have just wanted me out of his hair and so told me I just had to live with it. Thoughts?


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#2 of 10 OFFLINE   Leo Kerr

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Posted May 04 2010 - 10:53 AM

I can give you some comments on the general technologies, but I can't be terribly specific about models and cases.

First, a possible explanation of your issue:

The first plasma displays had a major problem with where the black-level was.  If you had a gray-ramp going from white to black, at some point "near" black, there would be a "shelf" as it went from, say, 10% output to 0%.  It was a pretty big step from "lowest displayable level" and "panel at zero output while it still has power."  As the technology improved, they were able to reduce that shelf-point closer to the actual 0% level.  And to cover the gap, they would impose a "dither" -- adding in some very minor random variation to help try to pretend to have a better lower-level cut-off then they actually had.  Some worked better than others.

Even now, although it's been a while since I've seen a prime-generation plasma, I suspect that there is still a cut-off point, with a little bit of dithering on perhaps all but the very best (expensive) plasma displays.

The girlfriend's LCD panel works in an entirely different manner.  It has a backlight that is always on (unless it's a modern dynamic LED one, but let's ignore that possibility for the moment).  The pixels are actually "gates" or "valves" that allow light to pass through them; the gate set by adjusting the strength of the polarization of the individual pixels.  (behind that is another polarized plate.  If the gate is across the master-plate, then no light passes through that cell.  If it's in-line, then all the light passes through.  And if it's 1° off of crossed, then perhaps 0.8% of the light passes through.)  Because of the light being always-on, and the smooth adjustability of the polarization, it's perfectly possible to have a static, rock-solid image.

The plasma, on the other hand, is generating light, and if it's trying to generate something below it's actual working-range, it'll start doing pulse-width-modulation.  And, for some reason -- probably because the green is pretty close to your eye's peak sensitivity curve -- you're seeing the green flashes.  And with the still frame, it's still doing the flash-dithering.

Now.  You're implying that it didn't used to do this, and, given the size and resolution of the set, I'd be surprised if it was supposed to be this bad.  Since fiddling a hidden knob on a board "improved" it, it makes me wonder if something on that board is going bad, and you might be better served by having whatever that board is, be replaced with a new one, 'cause it'll probably continue to degrade.

(In case I didn't cover it clearly, the reason why you don't see any of this in the bright areas is because they're still in the "happy" zone for the plasma display elements, and they don't need any trickery to perform well.)

Did I cover everything I think I should have?

Leo


#3 of 10 OFFLINE   Phil Carter

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Posted May 04 2010 - 01:09 PM

Leo -- I can hardly see how you could possibly have covered anything else. :) Thanks for the very detailed reply.

The TV is just over a year old, so I don't know if it quite falls into the first-generation range you mentioned. My Google-fu turned up several threads and links about plasma TVs with "green dots" issues, many of them dating back to five years ago or before. Several of them refer to issues with, and replacement of, the "Y sustain" board. Maybe that's the one in this case, but I'd have no way of knowing.

I, too, think that there's an issue with whatever board the tech was adjusting, and think I'd much rather have it replaced. The problem now will be convincing the third-party company to actually do so -- the tech didn't seem to agree with me on the severity of the issue and was more inclined to dismiss it. On the other hand, he also said he'd never noticed that sort of thing before, so how the hell does he know whether or not it's normal?

I love the deep blacks the plasma produces (when they're not speckled with green, that is -- even the black bars above and below 2.35 films have these dots, for cryin' out loud) but sometimes I wonder if I might not have been better off with an LED / LCD set. Less care and feeding involved with those. :)

Thanks again!


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#4 of 10 OFFLINE   Leo Kerr

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Posted May 05 2010 - 11:06 AM

I've always thought plasmas looked better than LCDs...

anyway, your plasma is new enough that it shouldn't be an issue.  The worst of it was probably about 10 years ago. 

As for the tech, he's not the one living with it.  But given that he's the third-party, then he's not the one paying for it, right?  And given that this problem didn't happen when it was new (right?) it's a degenerating part, and therefore needs to be replaced.

As you point out, there are all sorts of unreasonable people that have to be convinced first..

Good luck,

Leo


#5 of 10 OFFLINE   Phil Carter

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Posted May 05 2010 - 02:23 PM

Right on. Time to make a phone call back to the repair place, I think. Now to try and breach the language barrier (the problem was exacerbated by the fact that this tech spoke very poor and heavily accented English; I understood only about half of what he said at any given time).

I definitely agree that plasmas look better than LCD displays. LCDs still look too "digital" for me, too heavily video processed. I see video noise with most of them when I'm at stores. Here's hoping my plasma can be fixed without too much more of a fuss.

Thanks again for the detailed reply.

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#6 of 10 OFFLINE   Gregg Loewen

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Posted May 06 2010 - 01:04 AM

try new cabling

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#7 of 10 OFFLINE   Phil Carter

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Posted May 06 2010 - 02:23 AM

Gregg: The issue is visible from both sources (PS2 using component cabling and PS3 using HDMI cabling). Also, I replaced the HDMI cable with no change (mentioned in the initial post). But thanks for the suggestion!

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#8 of 10 OFFLINE   todd gar

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Posted December 20 2010 - 03:54 PM

Phil,

Am wondering if you ever got this resolved? I just purchased a Samsung PN63C8000YF. LOVE the TV, but also just noticed the flickering green dots and started to Google. Your post seemed to most match my problem. The dots I see are VERY small- no bigger than a single pixel and are visible most clearly when I'm close to the TV. Like yours, my dots appear at the near-black levels. Tried new cables, tried connecting directly to the TV (as opposed to through the receiver), tried several devices. All provide the same result- green dots. Did you ever eliminate your dots? I'm still within the return period and am thinking about replacing for the same model to determine if my unit is defective.

Thanks,
Todd




#9 of 10 OFFLINE   Phil Carter

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Posted December 21 2010 - 08:52 AM

Todd,


Fry's Electronics sent a repairman out to my place twice. The green dots lessened as he adjusted something inside the set, but didn't go away. Then he adjusted something else and the green dots went away completely but the colors were out of whack elsewhere on the set. Eventually he admitted that he couldn't fix the problem and so they replaced the set (since it was under the 2-year protection plan). Unfortunately, the set they gave me as a replacement is one or two tiers lower in the Samsung hierarchy than the one I had. There are no green dots on the new set, but neither does it have some of the features that my old one did. Still......new TV, I can't complain too much.


I think in your case you're better off returning it and getting a new model. See if you can get them to test the replacement instore (when they sent a repairman out, I had my PS3 loaded with a scene that showed the green dots very easily).


That said, I'm not sure I would get another Samsung plasma after the issues I've had. They still have the lead on LED/LCD televisions, but I think Panasonic has taken the lead for plasmas. Too bad Pioneer isn't in the market anymore.....


cheers,

Phil


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#10 of 10 OFFLINE   Jburlison

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Posted January 17 2011 - 08:17 PM

First of all, thanks to everyone for all of the information given in this forum.  It's been a lot of help.


I have a Samsung PN50A450  (just like the 550, only 720p) that was/is having the exact same problems. The "flash-dithering" was subtle at first, but got progressively worse. I bought the tv 2 years ago, so I'm obviously way outside of my warranty.  It looks like I am going to have to replace the Ysus board, but until I do, I just wanted to post a temporary fix that worked for my set.


I changed the mode in the picture settings.


I know it's a videophile's worst nightmare, but I took the mode it was in, "Standard," and changed it to "Dynamic."  The new mode certainly gives innacurate colors but it instantly solved the problem.  I'll take fake skin tones over that awful flickering any day.  And again, it is just a temporary fix.


I've never had the tv professionally callibrated, but I did of course try and callibrate it myself.  All of the settings fell within the ranges of every online recommendation.  So I really do think this problem has to do more with poor product quality and less with something, well, that I did wrong.  I guess I should have compared "Y Sustain Board" specs when shopping.


I hope this somewhat helps.  Thanks again for all of the previous posts.


Jake