Re: Weird distorted shapes

From: Colin Davies <colin.w.davies_at_btopenworld.com>
Date: Tue Mar 04 2014 - 15:39:03 EST

As Clay says....

 To be more useful I'd want to see the schematic for the
deflection section and/or the layout. Curvey/distorted things like that
could be related to opamp speeds or outputs getting too close to the rails
or L/C or maybe power...

  ----- Original Message -----
  From: Joel Griffin Dodd
  To: vectorlist@vectorlist.org
  Sent: Tuesday, March 04, 2014 8:21 PM
  Subject: Re: VECTOR: Weird distorted shapes

  I spoke to Doug Snyder from Atari who, apart from designing the System II hardware, also worked on a fair bit of the XY drives and outputs for many of their games. He said that there was cross talk between the Axis which is what was causing the curving and to isolate a letter on the scope then measure the voltage change for a stroke to see if there are unwanted voltage changes in the direction of the stroke that should remain straight. If there are non then it could be the yoke, if there are then the concern is that there is cross talk in the XY drives.

  Trouble is I have no idea how to isolate the stroke of one letter on my scope as I'm not that proficient.

  On Tue, Mar 4, 2014 at 12:07 PM, Colin Davies <colin.w.davies@btopenworld.com> wrote:

    The problem looks more apparent in this other picture... See how the 'straight' lines have a curve to them...

    https://www.dropbox.com/s/i1r76l4dif9vv2w/2014-03-02%2020.10.19.jpg

    ----- Original Message ----- From: "Clay Cowgill" <c.cowgill@comcast.net>
    To: <vectorlist@vectorlist.org>
    Sent: Tuesday, March 04, 2014 6:46 PM
    Subject: RE: VECTOR: Weird distorted shapes

>Look at this screen shot of another builders results...

        https://www.dropbox.com/s/owa3vq5l6f0lgv2/100_3343_zps3521fb63.jpg

        Notice the blue is perfectly formed, but the green is all messed up

      That looks to me as though the green channel amp is slow to turn on. The
      vectors look pretty straight-- they're just either 'fading in' (or 'fading
      out' depending on the direction of the draw I suppose) before reaching the
      end of the line. Could be a tube issue as well. Looking at the green color
      output vs. a deflection channel (or two) would probably show the problem on
      a scope.

      There might be a little high frequency 'jitter' in there somewhere that's
      causing the hash on some of the green verticals. Hard to tell with a
      picture-- really need video there. Also could just be that the shadow
      mask/dot pitch on the tube is pretty big and sometimes the green verticals
      are straddling the mask and appearing on one side or the other.

      For Joel's original problem, I would probably try to trace things through
      the deflection section with the scope-- put the Star Wars boardset X output
      on one channel and then follow X through the deflection section with the
      other channel. Set the volts/div to try to keep the waveforms about the
      same vertical size on the scope and compare them visually. You should be
      able to see that amount of difference/distortion on the screen so you should
      be able to see when it appears in the deflection board. (Hard to debug
      without knowing the design, but I'm assuming there's probably some sort of
      pre-amp that you could look at before it gets to a power-amp stage.)

      It does kinda look like its more prominent on short vectors which is
      probably a clue. To be more useful I'd want to see the schematic for the
      deflection section and/or the layout. Curvey/distorted things like that
      could be related to opamp speeds or outputs getting too close to the rails
      or L/C or maybe power...

      -Clay

      ---------------------------------------------------------------------------
      ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
      ** Please direct other questions, comments, or problems to chris@westnet.com

    ---------------------------------------------------------------------------
    ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
    ** Please direct other questions, comments, or problems to chris@westnet.com

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Tue Mar 4 15:39:15 2014

This archive was generated by hypermail 2.1.8 : Tue Mar 04 2014 - 15:50:00 EST