Pleas Help! - calibrating Akai CFT2791 (Samsung clone)

Discussion in 'Archived Threads 2001-2004' started by Jesse Clift, Oct 19, 2002.

  1. Jesse Clift

    Jesse Clift Agent

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    Hello all,
    I am having a serious problem with my Akai CFT2791. The set will change black level over time. The clearest example is when watching a 2.35:1 dvd in widescreen mode. In widescreen mode, the set "squeezes" to about a ratio of 1.85:1. So when watching a 2.35:1 movie, I have really dark 1.85:1 bars and then less dark bars extending from those that frame the 2.35:1 image. I calibrated the set using Video Essentials and I use mattes when I watch movies so the difference in black level of the bars does not bother me. After watching a movie with the mattes off for a while, I can actually see the bars that are part of the anamorphic image darken and approach the black level of the 1.85:1 "squeezed" bars. When this happens the overall picture becomes MUCH too dark.
    I believe that the set has some kind of automatic black level adjustment that is the culprit. I tried disabling it in the service menu using advice found in this thread. First, I tried adjusting "B stretch-BTHR", "B stretch-BTLT", and "B-BAM" in the video adjust 2 menu all to zero. Second I tried adjusting "Peak Threshold" in the video adjust 3 menu to zero. After making these changes the set still does not hold black level.
    If I turn the TV off and then on after the screen has darkened, black level returns to normal. Sometimes it will then stay that way untill the end of the movie and sometimes it will darken again. Also, when adjusting the brightness using the high and low APL pluge test signals from VE, I cannot get the black bar on the left to show up at all.
    If anyone else knows how to fix this problem in the service menu I would be grateful. Also, if anyone has a phone number for Akai/Samsung tech support that would be a big help. Thanks.
    -Jesse
     
  2. Jack Briggs

    Jack Briggs Executive Producer

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    Jesse, the Akai clearly has to weak a power supply to maintain its black levels in relationship to brighter images appearing onscreen. This problem is even common to much more expensive sets.

    Thing is, the only way to get rid of those "lighter" black bars within the 16:9 window is to reduce the white and black levels accordingly. Properly calibrated, the TV should maintain the letterboxing bars within the 16:9 window. You are overdriving the set.

    And the simple fact is, home theater should be experienced in a darkened environment. In such cases, the picture should not then be "too dark."
     
  3. Jesse Clift

    Jesse Clift Agent

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    Jack-

    Can you please explain what "overdriving the set" means? My viewing environment is usually almost completely dark when I'm watching movies (dorm room). I am aware that a properly calibrated set will appear a bit darker to the uninitiated. I had to explain this to my parents when I calibrated their Sony XBR. Even in a completely dark setting the set will darken to the point where, for example, facial features will be completely lost in shadow.
    I do suspect my white and black levels are off, but how can I calibrate correctly when the left black bar in the high and low APL pluge test signal doesn't even display on my set? Is there another test signal I can use to adjust black level that doesn't use two black bars against a black background?

    -Jesse
     
  4. Jesse Clift

    Jesse Clift Agent

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    Jack-

    Do you think that it is a power supply issue and not some kind of automatic black level adjustment? In a previous thread (see link in initial post), other Akai owners were dealing with similar black level problems. There would be sort of a "flash" and black level would shift. That is what my set does.
    Also, if it helps my calibrated values right now are as follows:

    Contrast- 31
    Brightness- 34
    Sharpness- 0
    Color- 21
    Tint- 50R/50G

    -Jesse
     
  5. Jack Briggs

    Jack Briggs Executive Producer

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    If the set has some sort of auto black-level "function," it should be defeated—I'm speaking of the Akai unit.

    "Overdriving" means driving the set's light output beyond what its power supply can safely handle (and long after blooming has occurred).

    Increase the Sony's white and black levels approriately until at least you can see some detail in dark scenes (that are actually on the film).

    But what you're describing about what Akai owners are seeing does sound to me as if the power supply is simply too weak to maintain the black level retention.
     
  6. Jesse Clift

    Jesse Clift Agent

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    Jack-

    Thank you for clarifying. I appreciate your input.

    Anybody else out there have experience with this set?

    -Jesse
     
  7. Chris_JH_Mo

    Chris_JH_Mo Auditioning

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    I recently purchased this set and so far I'm quite happy with it. There are two problems I'm having difficulty fixing currently, one is that I haven't yet been able to fix the convergence issue (any input appreciated) and I also just noticed an annoying problem today: The top of the film screen (i.e., top inch or so of the picture, regardless of mode, flickers/tremors a little bit). Anyone have any experience with/knowledge of how to fix, this annoying little problem? Thanks much!
     

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