Re: Noticed new vector monitor discussions, this is my input...

Thanks for your input. Here are some comments on it:

>...winding your own yoke may well be almost impossible...

I agree and I plan to have them done by a standard yoke winding company.

>...electronic pin correction...

Thanks for mentioning it. If pincushion is a problem, I can inject some of the y signal into the x drive. I'll probably put a trimpot in for this adjustment. I noticed that some of the 19" units seem to do this with one or two turns on a separate winding too. I need to take the time to understand what Clay's display corrector is all about too. http://www.multigame.com/display.html

>...double the drive-use 2 driver boards, and 2 sets of outputs...

The topology and devices are all wrong for that use, especially the way you described using them on each side of the winding. They use the ground side for feedback, and feedback is what will get you in trouble every time with this.

The closest thing you could do that would to beef up the drive wouldn't require a second control board at all:

Just get an extra set of identical transistors, put it them parallel, with the first set, and connect the outputs of each through a resistor like 1 ohm, 3 watt.

>How about boosting the voltage to the board?
>The driver bias could be adjusted to compensate,
>and getting hi-power transistors at 6 Amps and
>200 Volts are possible now.

I don't quite understand what the voltage increase is supposed to accomplish. You can try this right away by bypassing the voltage regulator transistors on your power supply. In fact, there is an evil tech document, http://www.gamearchive.com/video/manufacturer/atari/vector/monitors/wg_color/final_solution.txt, that someone actually reccomended this. (What were they thinking?)

The power dumped across a transistor (or any device) is going to be precisely equal to the voltage across it times the current through it. The current, in a correctly working drive, at any given moment will be the same no matter what the voltage input is becuase the current is what is fed back.

The conclusion to draw here is that you want the voltage to be as low as you can make it so that you are just above the threshold of degrading performance. Increasing the voltage would be desirable only if you couldn't get enought deflection or your draw speed was being limited (warped vector draws).

In your case, where you are going to make a custom vector game from scratch, maybe higher voltage would be good, but I wouldn't do it ever unless the monitor couldn't keep up with the game.

By the way, I think those existing transistors are 10 amp 100V devices. Good enough on paper.

Have a nice day,
James
====================================
  ----- Original Message -----
  From: Aaron Howald
  To: vectorlist@lists.cc.utexas.edu
  Sent: Friday, October 22, 1999 2:49 AM
  Subject: Noticed new vector monitor discussions, this is my input...

  Hi to all of you! Since I work on TV's for a living, I thought I'd add my input to the fray...

  Firstly,I think winding your own yoke may well be almost impossible.
   Unlike a standard coil (like a relay) the windings are staggered, crossed over on each
   other in a wild fashion, and precisly placed. All of this is for convergence assist+pin
   correction on some yokes. Doing this by hand is a grisly task, at best!
  Second, some obsevations on standard tv yokes. 13" tv's NEVER have any electronic pin
    correction at all. I assume this is because of the small screen size...
   19" sets generally do not either, but most 25" do, and 27"-up ALWAYS have the correction.
    I assume with larger max deflection angles+longer beam travel, it becomes a nessessity.
    There is 1 25" set I know of that has no correction, and looks fine-other sets use a complex
    board to do it...but I wonder, if the yoke can be wound to fix the pin, why use a more
    expensive correction board?

  Third, I thought of an easy way to double the drive-use 2 driver boards, and 2 sets of outputs!
    Drive board 1 (say a P327 from a WG) is X only, 2nd for Y. Feed drive 180 deg out of
    phase to one input, and connect the yoke winding between the 2 outputs. Has anyone tried this?

    I'd like to, but I need a P327 WG defelection board. Anyone have one for sale?!

    The yoke would have 2X the "kick" on it, for 2X beam draw speed. DC hold current would be the
    same, but drawn from both supplies (+-) equally (at 1/2 voltage each Of couse 2X parts=2X
    chance of failure!
    How about boosting the voltage to the board? The driver bias could be adjusted to compensate,
    and getting hi-power transistors at 6 Amps and 200 Volts are possible now.
  I'm still working on my game system-slowly. It will be awsome when done-A modded 19" WG
         with a vector drive board of my own design, with a computer driver program/game engine
        of my own design.

  If I can get a deflection board, I am keen to try the board doubling idea and the voltage increase.
  Keep up the stimulating conversation!

  Aaron Howald
  ahowald@w-link.net
Received on Fri Oct 22 07:25:32 1999