Re: G-05 monitors

At 02:58 PM 8/6/97 -0700, you wrote:
>
>Zonn said:
>
>All said and done if you're re-designing the board this should be an easy
>part to replace, (I wouldn't use either of the above) it just needs to
>switch positive and negative voltages. The current handling is not great,
>and can easily be calculated (I would if I had a schematic here in front of
me).
>
>
>..actually, I had meant to ask about this. The deflection voltages are bipolar
>with the center of the screen at 0V,0V ?

That's correct. I'm sure that's true of all X/Y, since 0,0 means zero
current through the yokes. This is what you want when your not drawing
anything.

On the other hand the software sees 0,0 as the lower left hand corner of the
screen so there is some offseting going on in the DACs which I've never
bothered to look into that you'll need to re-create. To set the CRT trace
(and therefor the value going into the X/Y deflection amps) to 0,0, the
X-DAC would be loaded with 512, and the Y-DAC with 384.

>As long as I was hacking, I was going to add a deflection timer too, so if the
>incoming X or Y values were off scale for too long, it would shut down the
>deflection amps and turn on a spot killer.

The color card did a very nice job of *clipping* the X/Y signals. It took
them a couple more OP-AMPs (and power transistors) to do it, but they do a
*hard* clip of the signal right past the edge of the monitor. Tempest sure
could use something like this in those zoom modes that fry deflection circuits!

If you ever plan on building a Color Card convertor you're going to need to
recreate these circuits since Boxing Bugs intentionally overdrives the X/Y
signals, since it was known no damage would result, and software clipping is
slow, and a pain.

-Zonn
Received on Wed Aug 6 15:25:42 1997