Astigmatism and raster position interactions.

Discussion in 'Projectors, Screens & Video Processors' started by cosaw, Mar 15, 2006.

  1. cosaw

    cosaw
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    Well been tweaking pots and stuff internally and turning the electronic focus pots up and down does show that the astigmatism wants doing next. The pj is a Barco Data 500, which is basically the same as the 800 but has smaller tubes and lenses.

    I've read that altering astigmatism will cause a raster shift and in turn the rasters will need to be recentered - you can do this a few times iteratively it seems to get best results. Currently I've been doing the manual raster shifts with the trimpots on the North/South and Vertical board in order that I don't need to do a raster shift in the software.

    The question: Is this the only way to do manual raster shifts on Barcos. I've read on other pjs that there are raster centering magnet rings near the deflection coils similar to the astigmatism rings/magnets. Can't seem to find these rings on the Barco. Any ideas? Thanks in advance.
     
  2. Boy Lex

    Boy Lex
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    I wouldn't have thought you'd get much of a raster shift unless it's really radically out.

    I'd guess that you could design the tube to have a raster adjust on the tube, but that would involve physially moving the magnets around, which doesn't seem the smart way of doing things... I've never seen a tube sonys or toshibas that has an adjust like this... So I'd guess that the trimpots are the only way to go. As far as I'm aware the only other adjustment that can be made on the tube is deflection angle (and I guess raster size if you want to move the coils in and out).
     
  3. cosaw

    cosaw
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    Hi Lex,

    Pretty much what I thought however I'm sure that some pjs have raster centering rings/magnets. I'll have to find the guide where I read it. I think the NECs do - check this link form Curt's:

    http://www.curtpalme.com/Astig.htm

    Check the pic and how the metalic astig rings look with tabs (different than on the sony tubes) - now look forward to the deflection coil and you'll see similar rings with tabs just behind the deflection coil - I'm sure that these are raster centering magnets. Barcos obviously don't have them which is nice as its one less reason to have to put your hands inside near HV. Still all yokes could do with a tiny amount of leveling so it seems I'm gonna have to get my hands dirty sooner or later.
     
  4. Boy Lex

    Boy Lex
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    Well if everything is working properly, I wouldn't be as worried about touching the astig etc on the tube. You want to be careful of those 'live heatsinks' think they are only 240v, but I've had a couple of shocks there! The way I see it, the HV is supposed to be contained within the tube and the tubes should be grounded by (usually) a bare flat metal cable near the face.... I guess this is the thing to ckeck... As long as that is secure - sparks should not fly towards you!

    Legal disclaimer:
    Boy lex takes no responsibilty for organising funeral arrangements in the event that your projector disobeys his perceived laws of physics and stops your heart beating.
     
  5. cosaw

    cosaw
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    ;) I know what you're saying lex.

    I wouldn't like to get any shocks :eek:

    I always wear rubber gloves and one hand and insulated tools even when I'm pot tweaking.

    I've drilled a hole lengthwise into a wooden clothes peg and extended its reach with a universal joint and some splines from my old technics lego stuff. The clothes peg clamps directly on to the astig knobs and allows easy adjustment without me getting my hands deep inside. I'll still wear rubber gloves though! When I' come to level the deflection yokes I'm gonna knock up a large wooden spanner which will seat on the square part of the deflection coils and allow me to turn with more accuracy and safety than using a bare hand. Rubber gloves also of course :)

    Limiting risk is high on my agenda - I'm not qualified in this field and am a little clumsy at best so I take every precauiton.

    The ground leads are well seated on all tubes by the way but thanks for reminding me. I feel I ought to do astig cos its way out on green.

    Cheers for the input as always!
     

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