Is this a 60Hz Hum?

Discussion in 'Archived Threads 2001-2004' started by Doug_L, Feb 19, 2002.

  1. Doug_L

    Doug_L Stunt Coordinator

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    Here's my problem:

    When watching extremely dark scenes (ie: at least 75% of frame is black or near black) there is a slight, periodic, brightening of the entire screen (although it could be just the letterboxed frame). It seems to happen about once a second (or 60 times a minute), and is really only noticable when the frame is dark and static (just re-watched 2001 and it was really apparent on 3 or 4 occaisions (I've also noticed this on other DVD's as well).

    Details about my setup:

    DVDP: Pioneer 525 (interlaced output only)

    TV: Loewe Calida 32" SDTV with built-in, non-defeatable line-doubler

    Monster Power Center HTS2000 (all power through this)

    DVD hooked up to TV using Ultralink Gold s-video cables (auto 16:9 detect only works with s-video); this cable does not run along any others (power or line level) but does have about 2-3 meters of play in it, which is currently loosely coiled

    TV is in 16:9 mode, which shows no picture/raster lines outside of 16:9 frame

    Not sure what other info is needed; ask and ye shall receive

    So I'd assume that this is some sort of power hum issue. If so, what's going on? Does it take more power to create black than white? My TV does a pretty good job of holding black at black with a variable APL, but is it trying to draw too much power? Is this happening with all images and I only notice it on the really dark ones?

    And here's to most important question: What can I do to fix this?

    All help is appreciated.
     
  2. Doug_L

    Doug_L Stunt Coordinator

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    Help! Please, anyone?

    This will be my only bump.
     
  3. Steve Berger

    Steve Berger Supporting Actor

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    There are so many variables involved that pinning down the problem could take a lot of time and experimenting.Try the following successively.

    1: There are two types of s-vid jacks using different grounding methods. This is an issue with some Sony TVs causing this exact symptom so try a different cable.

    2: Unhook all cables and cords except TV and DVD power and S-vid cable (even audio) this is to remove the chance of a ground loop (cable TV interference has been known to cause this symptom). Try more than one s-vid cable also.

    3: Try a composite video cable. Some DVD players have a bug in their S output.Borrow a friends (different brand) DVD player.

    4:[or maybe first) Try a movie verified as not having macrovision encoding. Some TV designs react to macrovision just like a VCR does. This would require a circuit modification from Loewe to resolve.

    5: Don't reconnect any cables until the process is complete because more than one thing could cause the exact same symptom.

    Hope this helps but these are just basic troubleshooting techniques for interference in general.

    Oh , BTW 60hz interference is usually seen as bands of noise floating through the picture .

    6: I almost forgot that the ABL circuit in the TV can cause this also . Adjusting brightness, contrast, black level will affect it as will black level settings that some DVD players have as options.This would require a manufacturer redesign if adjustments didn't cure it.

    I'll probably think of a few more things at work but this should get you started.
     
  4. Doug_L

    Doug_L Stunt Coordinator

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    Thanks, Steve. I'll try and find the time to give your suggestions a shot this weekend.
     
  5. MarkDesMarais

    MarkDesMarais Stunt Coordinator

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    Doesn't sound like grounding/interference to me. . . I like Steve's 4 or 6 above.

    As for power, a black image takes less, not more, so it doesn't sound like a power supply problem either.

    Does it only show with the DVD player?

    Does your TV do the squeeze? (Assuming it is 4:3)

    Try masking off the active area and see if the black bars are indeed brightening.

    I saw something similar on my 'rents old 27" Mitsu tube when my brother played a DVD from his laptop through it. . . a little more extreme though, we could see it in all types of scenes.

    Markd
     

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