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Astigmatism correction on TW40X81

Discussion in 'Archived Threads 2001-2004' started by Michael_V, Feb 2, 2002.

  1. Michael_V

    Michael_V Second Unit

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    Time to give the old Tosh an overhaul. Went through a fairly extensive geometry correction tonight, following the directions given by Tom Herman on the Keohi site, although using the centering magnets to center the screen via the TV generated grids left the screen off-center approximately half an inch, and I ended up using the centers on my convergence grid overlay instead.

    Anyway, I wanted to try to even out the focus on the sides since this has always been an issue, particularly on the right. I tried to implement the instructions given by Stephen Smith (CRT ASTIGMATISM ADJUSTMENT ON TOSHIBA) also on Keohi, but could not tell what was meant by the 2-pole and 4-pole magnets used to make these adjustments. Consulting the online service manual shed no light either.

    Can anyone help me find these magnets? :b

    Thanks!
     
  2. StephenMSmith

    StephenMSmith Stunt Coordinator

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    The service manual has a nice drawing of the yoke that identifies the 2, 4, and 6-pole magnets, as well as the centering rings. Are you sure you weren't looking the user manual instead? The 3 pairs of pole magnets are right there in the middle of the yoke and hard to miss, but the centering magnets are at the very top of the yoke, hidden behind the metal frontplate.

    However, these rings are for adjusting the spot size (ie. achieving the the smallest possible spot size) rather than adjusting a general left side/right side focus imbalance. For that, you need a Scheimflung (sp?) adjustment which no rear projector has AFAIK. But you can simulate it by putting a super thin washer or two under one or more of the lens assembly screws. The idea is to tilt the lens ever so slightly relative to the mirror in the direction that gives you the best overall screen focus.

    Steve
     
  3. Michael_V

    Michael_V Second Unit

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    Steve,

    Thanks for the response! The washer trick sounds promising! Will try it once my set is back up and running!

    Mike
     
  4. StephenMSmith

    StephenMSmith Stunt Coordinator

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    Uh oh. What happened to your set? AFAIK, the risk with those various mechanical yoke adjustments is limited to just electrocuting yourself.

    I went to UVa, btw ('90). Fun times! How's Charlottesville?

    Steve
     
  5. Michael_V

    Michael_V Second Unit

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    Stephen,
    Sorry so long in posting! Busy times here!
    Anyway, the problem with my set has nothing to do with the mechanical yoke adjustments. It has everything to do with the so-called VPOS glitch reported on the Keohi site: trying to adjust VPOS with the component input active, getting no response from multiple button presses, and then discovering one or more of the rear inputs don't work.
    I lost the component inputs for progressive signals only, did a QA02 reset, and promptly lost my tuner! [​IMG]
    Thank God I purchased an extended warranty from onecall! They are sending a tech out to my house next week, probably to replace the EEPROM, which will hopefully restore my set to its original splendor.
    BTW, Charlottesville is great! I am finishing up a radiology residency at the UVa medical center. Probably not having as much fun as you had in college, though!
    Mike
     

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