Keohi HDTV



Powered by Keohi Web Design


Perfect Geometry

<< Back to Service/Designer Menu Page

Tip from Stephen Smith:  "Yes, it's possible tp have perfect geometry .... because I have it. It took many, many hours but my TW56X81 has absolutely perfect geometry in all TW modes with less than 3% overscan (2% left and right in TW1). You absolutely must have the convergence overlays to do it. You can't buy them for the 56" so you'll have to make your own.  Click here for info on making your own.

I basically did this:

  1. reset geometry params to native defaults
  2. adjust astigmatism, alignment, and centering magnets on each CRT (see instructions on how to do this)
  3. verify and adjust in designer menu these "dynamic quadruple focus" params if necessary (some sets -- like mine -- are not set to these values at the factory) as follows:
    STRH, 1STH, 2STH, 3STH: 7B
    STRP, 1STP, 2STP, 3STP, STP1: 95
    VLD, 1VLD, 2VLD, 3VLD, VLD1: 44, 44, 4B, 4C respectively
    STH1: 80
    STP2: 99

    Note: these values may only apply to 56" and 65" screens! If your TW40 has different values you should leave them as is initially
  4. align Full, TW1, and TW2 to overlay grids precisely
  5. use tape measure to check diameter of Full screen circle (circle hatch pattern) both vertically and horizontally, and adjust height or width as needed. For me at least, the aligning Full to the overlay grid gives me 3% overscan on the top and bottom, but I needed to decrease the width quite a bit for a perfectly round circle, which consequently reduced left and right overscan to 3% as well.
  6. correct any vertical grid line curvature that resulted from reducing picture width using overlay grid as reference.
  7. adjust screen centering for Full, TW1, and TW2
  8. adjust HIT of TW2 (which share WID w/Full) using circle hatch for correct proportions to WID (you can temporarily increase WID back to overlay dimensions to straighten out the resulting horizontal curvature)
  9. increase WID of TW1 to same as WID of Full (IOW,

It's a lot of work and I only did it because my set was not tuned properly at the factory and shipped with visible linearity and centering problems within all TW modes. I can give you details if you think you want to try it, but unless your unhappy with your present geometry, I probably wouldn't. Remember, this is basically irreversible, ie. you can't just restore your default values if you don't like the result."