1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Straight vertical geometry but the screen still bends???

Discussion in 'Televisions' started by Jimmi, Apr 19, 2003.

  1. Jimmi

    Jimmi
    Active Member

    Joined:
    Sep 8, 2002
    Messages:
    501
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    28
    Ratings:
    +29
    I have a Panasonic widescreen and although the geometry is pretty much vertically straight, the image still occasionally bends badly.
    I've noted that it tends to happen during bright scenes, such as strong daylight coming through the widow of a room. This cause's the image to pull (usually inwards) so that vertically straight objects appear to bend and twist.
    Another example would be lamp posts bending at the top if the scene is too bright. It's almost as if the higher level of contrast/brightness is knocking the vertical geometry out of line.

    Is there an explaination for this or an official wording of the problem ?.
    Is it something Panasonics are famous for or does it effect all crt sets ?.
    I had a philips and a sharp set before my panny and I never noticed the problem on either of those sets.
     
  2. Squirrel God

    Squirrel God
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    It happens on all sets, but naturally some sets are worse than others for this (often because of cheap power supplies). Try turning the contrast down a bit.
     
  3. LV426

    LV426
    Administrator Staff Member

    Joined:
    Jul 14, 2000
    Messages:
    12,756
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Somewhere in South Yorkshire
    Ratings:
    +4,909
    It happens on all CRT sets, to a greater or lesser extent. It is, as SG says, poor voltage regulation in the power supply. Heavier transformers, etc., can minimise it which is why things like Loewe's are less prone.

    The only way to virtually guaranteed perfect geometry is Plasma/LCD.
     
  4. silent lucidity

    silent lucidity
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    I lowered the contrast and brightness on my p+ set to minimise the "black bars" problem.I only realised when I read this post that a beneficial side effect was an improvement in the sets geometry.Wondered why it hadn't bugged me for a few weeks!You'll be surprised how much you can lower those settings and still get a perfectly watchable picture,baring in mind the factory presets are set to "shop floor" levels.
     
  5. Squirrel God

    Squirrel God
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    You should really calibrate the set's contrast, brightness, colour (and hue for NTSC feeds) using something like THX Optimiser, AVIA or DVD Ultimate Platinum.

    BTW, I believe the technical term for the effect is "blooming".

    Sony incorporated some technology to counteract this in their recent sets, but I can't remember what they called it :( Works a treat on my LS60 though, even when the contrast is set to full :)
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
    Distinguished Member AVForums Sponsor

    Joined:
    Jul 13, 2000
    Messages:
    13,980
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Living in Surrey, covering UK!
    Ratings:
    +2,781
    Blooming is what happens when the phosphor is overenergised, it's not the term for the geometric distortion. It's as everyone has said before.

    The other benefit of turning down the contrast is the undoubted reduction in blooming giving a more detailed image.

    Gordon
     
  7. Squirrel God

    Squirrel God
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Thanks Gordon :)

    Is there a technical term for the geometric distortion?
     
  8. Gordon @ Convergent AV

    Gordon @ Convergent AV
    Distinguished Member AVForums Sponsor

    Joined:
    Jul 13, 2000
    Messages:
    13,980
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Living in Surrey, covering UK!
    Ratings:
    +2,781
    I'm suffering from a nightmare hangover just now and am having trouble remembering my name.......I think the geometric distrotion is just that, but it's cause is a DC restoration issue with the power supply as Nigel said.

    Gordon
     
  9. Squirrel God

    Squirrel God
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    LOL, thanks Gordon. Get well soon :D
     
  10. Jimmi

    Jimmi
    Active Member

    Joined:
    Sep 8, 2002
    Messages:
    501
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    28
    Ratings:
    +29
    thanks for the help guys.
    I'll try lowering the contrast/brightness.

    If it makes no difference is it the kind of fault I could request a refund for ?. (TV is a week old)
     
  11. LV426

    LV426
    Administrator Staff Member

    Joined:
    Jul 14, 2000
    Messages:
    12,756
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Somewhere in South Yorkshire
    Ratings:
    +4,909
    Not sure if this is 100% right but, with specific reference to changes in the picture's shape as the brightness of parts of the picture change - rather than simple geometry errors - I believe this is known as voltage regulation bounce - ie, it's caused by poor voltage regulation, and the image bounces. It's most noticeable, I find, if you watch a channel with a logo - and concentrate on the logo. Often worst on music channels because of the type of programming.
     
  12. Squirrel God

    Squirrel God
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Sounds reasonable :) Ta ;)
     
  13. Orbitalzone

    Orbitalzone
    Active Member

    Joined:
    Feb 23, 2002
    Messages:
    394
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    31
    Location:
    E.Sussex
    Ratings:
    +43
    Another good reason for reducing the contrast levels is to increase CRT life... as a former TV engineer, I often found the worn out CRT's happened to be from customers we knew had the contrast / brightness cranked right up.... whenever we'd visit the faulty TV we'd lower the contrast to give a proper picture setting... a while later we may go back to alter the TV or adjust the video and all the setting were back to max.... customers didn't like it if they couldn't see what was going in the shadows on Eastenders and other such dark and dingy soaps!

    Doh
     

Share This Page

Loading...