Samsung inverse picture

[vinceroger69]

Re: Samsung inverse picture

maybe put your t con voltages into tom66 spread sheet it will tell you if the voltages are correct
https://www.badcaps.net/forum/showth...gamma+voltages

[microvibe]

Re: Samsung inverse picture

I have same tv and a ln46a530 model. The 46 has a bad as15 gamma chip. The 40" has bad as19 chip. I have cpl salvaged tcons from other tv's with good as15 chips can I use as15 in the as19 board?

I cranked my brightness and contrast way up and backlight at maximum. It changed pic drasticly maybe op give that a try

[Davi.p]

Re: Samsung inverse picture

MVibe: "cpl" is? As15 is not the same as as19.

To the OP: gamma voltage seems about correct, strange, i would have bet tcon problems, but now i'm suspecting something wrong on the settings eeprom, would you like to do a service menu reset?

[attainteddragon]

Re: Samsung inverse picture

your gamma voltages are bad. there should be a steady gradient throughout the entire set and pin 5 is out.

you need your as19 chip replaced.

[Davi.p]

Re: Samsung inverse picture

Maybe i have understood bad the gamma voltages but for what i know theese voltage have to form a tipical gamma curve (like hyperbolic), since the screen is about white, don't it have to be like all near zero volt or 15 volt? (a flat line)..

[tom66]

Re: Samsung inverse picture

Maybe i have understood bad the gamma voltages but for what i know theese voltage have to form a tipical gamma curve (like hyperbolic), since the screen is about white, don't it have to be like all near zero volt or 15 volt? (a flat line)..

no.

Due to how an LCD panel works there are two curves around 1/2 AVDD.

Typical AVDD is 14-16V. Assume 15V, so the panel is biased around 7.5V. This is to avoid DC biasing the panel, which poisons the liquid crystal and causes "burn in". So a pixel with, say, 50% grey will be biased between -5V and +5V. To achieve this, panel VCOM is set to 1/2 AVDD, and pixels are written to 2.5V and 12.5V on every frame, alternately.





Because this causes some flicker on the image, this alternating charge is shifted across the panel in a checkerboard fashion. On some LCDs this is visible up close but many are imperceptible. A side effect is that if you scroll an image with a similar pattern on your screen, it will appear to violently flash. This flashing will not appear on a plasma display.

http://www.techmind.org/lcd/

[microvibe]

Re: Samsung inverse picture

By cpl I meant couple. I have few salvaged tcons with as15 chips just wondering if can use the as15 in place of as19.

[Davi.p]

Re: Samsung inverse picture

Thanks Tom for the huge post, i will try to decipher...

[diif]

Re: Samsung inverse picture

By cpl I meant couple. I have few salvaged tcons with as15 chips just wondering if can use the as15 in place of as19.

No, the AS15 is different to the AS19. They are also quite sensitive to heat, I'm not sure it would survive removal and refitting.

[jurgyman]

Re: Samsung inverse picture

I remeasured a few testpoints. Five is higher Volts than Four.
Seems I should look for a replacement tcon, this time with an AS19 H1G?

1 15.29
2 12.78
3 12.00
4 11.46
5 11.85
6 10.71
7 10.03
8 9.04
9 8.06

[Davi.p]

Re: Samsung inverse picture

you are measuring old or new tcon?

[dskall]

Re: Samsung inverse picture

So should the gamma voltages be like the green line in chart? Each voltage less than the other?

[tom66]

Re: Samsung inverse picture

They should be a "monotonic function" which is to say increasing OR decreasing, but not both.

http://mathworld.wolfram.com/MonotonicFunction.html
https://en.wikipedia.org/wiki/Monotonic_function

All the gamma chip is, is a buffer chip for external voltage references, so it would also be possible to compare input and output by looking up AS15 schematic. However this is a lot more work.

[Davi.p]

Re: Samsung inverse picture

I'm deciphering but.. i have read that gamma correction is a color adapting between common video sources like videotapes, video-cine camera, that are designed for a CRT screen output, and the lcd screens that has a different output appearance, so is correct that the gamma voltages are made of a gamma correction curve plus its negative and is represented by curve in graphic (a)?

[tom66]

Re: Samsung inverse picture

I'm deciphering but.. i have read that gamma correction is a color adapting between common video sources like videotapes, video-cine camera, that are designed for a CRT screen output, and the lcd screens that has a different output appearance, so is correct that the gamma voltages are made of a gamma correction curve plus its negative and is represented by curve in graphic (a)?

Gamma correction is correcting the response so that an intensity of 100% and an intensity of 50% are displayed as approximately twice/half as bright as each other.

Video signals are linear. So your PC stores 50% bright as 127 and 100% bright as 255 (8-bit numbers.) On an LCD though those probably are represented as (for example), 20% voltage and 100% voltage. Gamma correction performs this translation. Doing it with external voltage references reduces the cost of the DACs. Think about it - you would need an 8+ bit DAC for each subpixel and 1080p display has >5,000 such channels. This would be WAY too expensive to make, so the gamma correction method is used, combined with a simple charge-shifting DAC which linearly interpolates between different levels.

[dskall]

Re: Samsung inverse picture

Ok well this is why I was a mechanic and not an engineer

[Davi.p]

Re: Samsung inverse picture

http://www.eizoglobal.com/library/ba...display_gamma/

the text is quite complex also due to english, is correct to say that maybe tv signal transmit in a gamma value negative to 2.2 for the use with crt monitors (it don't mention this, is my guess) that has a gamma of 2.2 (the result is a linear appearance) and most lcd have also a gamma curve of 2.2 to imitate CRTs or if them have an internal increase in bit color depth the curve becomes also more complex? BYE.

PS. If i dont have understood I swear I go into more detail

[tom66]

Re: Samsung inverse picture

No, you're getting CRT gamma and LCD gamma mixed up.

Different techniques.

[attainteddragon]

Re: Samsung inverse picture

Ok well this is why I was a mechanic and not an engineer

i hear that, i'm a gardener/arborist among other hands on trades, so i have to work hard to keep up some times.



on the other hand, to the op, you either need a replacement t-con, or locate someone to replace your as19 chip if you do not feel comfortable doing so.

[Chungalin]

Re: Samsung inverse picture

AS19 from the pictures looks very fake to me. I’d say it has been replaced with a cheap imitation. Very common. Almost all AS15, AS19, AS34 from E-CMOS are copies. E-CMOS doesn’t make them anymore. The question is not if it’s original, but, is it a good copy?