Question Regarding Pixel Misfires (Zoyd?) - AVS Forum
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post #1 of 6 Old 04-16-2012, 05:02 PM - Thread Starter
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I have a Samsung 51D490. Lately I've started to notice an odd phenomenon. On a cold start, the blue Samsung boot logo sometimes is speckled with a few black pixels. The pixels aren't totally dead, because they light up once the set comes on. And after the set's been warmed up for half an hour or so, the boot logo displays 100% correctly if I power cycle it.

Now, if it ended there, I'd just ignore it and say who cares. The thing is, I'm seeing it elsewhere, too.

If I load up a specific episode of Star Trek TNG and watch the actors' uniforms as the scene switches back and forth, the red and yellow uniforms become spontaneously littered with a dozen or so black pixels. If the scene doesn't move much, I can sit and watch the individual pixels come to life...almost like they forgot to turn on when the color in the scene switched from black to red or yellow, etc.

And again, the longer I have the TV on, the less this happens, until it reaches the point where I can play the entire scene back and only see maybe 1 or 2 of these black pixels.

Anyway, I was randomly reading through Zoyd's Samsung black level tweak thread and started to wonder if these black pixels might be misfires. If so, would following the methods in the black level tweak thread in reverse potentially solve my problem?

Thanks,
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post #2 of 6 Old 04-18-2012, 07:21 AM
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Originally Posted by serial_carpens View Post

I have a Samsung 51D490. Lately I've started to notice an odd phenomenon. On a cold start, the blue Samsung boot logo sometimes is speckled with a few black pixels. The pixels aren't totally dead, because they light up once the set comes on. And after the set's been warmed up for half an hour or so, the boot logo displays 100% correctly if I power cycle it.

Now, if it ended there, I'd just ignore it and say who cares. The thing is, I'm seeing it elsewhere, too.

If I load up a specific episode of Star Trek TNG and watch the actors' uniforms as the scene switches back and forth, the red and yellow uniforms become spontaneously littered with a dozen or so black pixels. If the scene doesn't move much, I can sit and watch the individual pixels come to life...almost like they forgot to turn on when the color in the scene switched from black to red or yellow, etc.

And again, the longer I have the TV on, the less this happens, until it reaches the point where I can play the entire scene back and only see maybe 1 or 2 of these black pixels.

Anyway, I was randomly reading through Zoyd's Samsung black level tweak thread and started to wonder if these black pixels might be misfires. If so, would following the methods in the black level tweak thread in reverse potentially solve my problem?

Thanks,

yes, what you describe certainly sounds like misfires. They are temperature and frequency dependent, the lower the temperature and the faster the change from dark to bright the higher the probability of a misfire. Manufacturers set the voltage and timing of the reset pulse to minimize this probability and if either one is too low you will start seeing this behavior. I'm not aware of any other mechanism for what you are seeing so increasing the pulse duration (Yrr pot) should clear it up at the expense of a slight rise in mll.
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post #3 of 6 Old 04-18-2012, 09:00 AM - Thread Starter
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Originally Posted by zoyd View Post

yes, what you describe certainly sounds like misfires. They are temperature and frequency dependent, the lower the temperature and the faster the change from dark to bright the higher the probability of a misfire. Manufacturers set the voltage and timing of the reset pulse to minimize this probability and if either one is too low you will start seeing this behavior. I'm not aware of any other mechanism for what you are seeing so increasing the pulse duration (Yrr pot) should clear it up at the expense of a slight rise in mll.

Thanks for the information Zoyd, I really appreciate it. I didn't want to bother taking the back off the TV unless I knew there was some chance of being able to remedy the issue. Now I just need to go buy an insulated screwdriver and get to work!

And this may be a dumb question, but I just wanted to clarify: When you say it's also temperature dependent, do you mean color temperature or physical temperature of the room/unit?
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post #4 of 6 Old 04-18-2012, 09:32 AM
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Originally Posted by serial_carpens View Post

When you say it's also temperature dependent, do you mean color temperature or physical temperature of the room/unit?

physical temperature, misfires on a static screen tend to disappear rather quickly after turning on the set if it's been off for a long time.

If you do feel up to tweaking I would measure and verify the voltages first. If they are off then setting them back to factory values (there is a sticker inside the panel) may be all you need and that will have a very minimal effect on mll. If those are ok then I would go to Yrr while displaying a screen with easily identifiable misfires.
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post #5 of 6 Old 04-21-2012, 08:14 PM - Thread Starter
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Just wanted to update: Checked my voltages, almost everything matched the proper values (one was off by a volt). Still had black dots, so I adjusted the Yrr pot as recommended, and this fixed the problem.

Thanks again! :-D
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post #6 of 6 Old 04-21-2012, 10:18 PM
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Originally Posted by serial_carpens View Post

Just wanted to update: Checked my voltages, almost everything matched the proper values (one was off by a volt). Still had black dots, so I adjusted the Yrr pot as recommended, and this fixed the problem.

Thanks again! :-D

Hello, check on an all black screen to see if you have misfires . AVS 709 HD full field pattern 0 percent IRE Color HCFR patterns. When I adjusted my YRR pot for better blacks tweak i had to back off the trim pot to the point where an all black screen had zero misfires eventhough it appeared on a full bright screen scrolling IR pattern that comes with the tv showed none. I might be also talking about two seperate issues. Thought I could give my 2 cents...
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