RE: Back to Bzone drawing on left side of monitor

On Thu, 5 Feb 2004, Joe wrote:

> Hmm, sounds like a project for Mr. O. Rubin... Is he on the list? Seeing

 . . Or Jed Margolin, designer of the hardware, author of The Secret Life of
Vector Generators and The Secret Life of XY Monitors, available from
www.jmargolin.com, and incredibly nice guy ? :-)

I e-mailed him last night, and had an answer this morning. He thinks it
would be the Window Blanking circuit. Which, if I had re-read his SLofVG
before mailing, should have been obvious. But I don't do this for a living.

Anyone who hasn't read it yet, I highly recomend his site and the Secret
Life articles. The detail on the operation of the VG is very usefull. Oh --
and he also has all his Atari VAX mail up too.

Here is his answer, for the arcives:

> To: Christopher X. Candreva <chris@westnet.com>
> Subject: Re: Battlezone hardware question
>
> Hi, Christopher.
>
> Thank you for your kind comments.
>
> I've looked at the pictures and the video, and as far as I can tell the
> pictures appear to be undistorted, so I believe the problem is with the
> Window circuit, specifically the Left Horizontal Window circuit made up of:
>
> D11 (LF13201 pins 9,10,11), C11 (TL084 pins 8,9,10), and B12 (LM319
> pins 7,9,10).
>
> The way it is supposed to work is that a Window Instruction (/LST) sets the
> Left and Bottom Window Edges.
>
> The Bottom Window Edge is stored in C70. C11 (TL084 pins 5,6,7) turns it
> into a Sample-and-Hold.
>
> The Left Window Edge is stored in C69. C11 (TL084 pins 8,9,10) turns it
> into a Sample-and-Hold.
>
> (There is similar circuitry for the Right and Top Window Edges.)
>
> The LM319 Comparators at B12 and D12 are always checking the stored Window
> Edges against the current X and Y positions.
>
> When the current position is outside *any* of the window edges, the beam is
> blanked.
>
> Note that the beam is still sent outside the Window. It's just that the beam
> is blanked so it is not visible. (The beam is not clamped to the Window.)
>
>
> Since the Bottom Window Edge appears to be working properly, the /LST
> instruction is probably working.
>
> I suggest you use a 'scope to see if:
>
> 1. the Window voltage is being written to Capacitor C69,
> 2. it is appearing at pin 8 of C11,
> 3. the window voltage is making it to the negative input of the LM319
> (pin 10)
> 4. the current X position is making it to the positive input of the
> LM319 (pin 9).
> 5. diodes CR9 and CR10 are not shorted.
>
>
> In the event I have guessed the wrong part of the circuit, you should look
> at the corresponding parts of the other sections of the Window circuitry.
> :-)
>
>
> Let me know what you find.
>
>

==========================================================
Chris Candreva -- chris@westnet.com -- (914) 967-7816
WestNet Internet Services of Westchester
http://www.westnet.com/
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Received on Fri Feb 6 13:34:23 2004