Re: XREF on Tempest?

On Mon, 1 Dec 1997, Ozdemir, Steve wrote:

> Can anyone explain what XREF and YREF does in the vector generator
> section of the non-Star Wars Atari color XY's? If these serve as
> references in the vector generator section of the PCB, could it be
> possible that these are voltages at a fixed value that XOUT and YOUT use
> as a baseline? If so, maybe my problem is that XREF is too high or too
> low and why everything on the bottom half of the screen is scrunched
> into a couple line? I should say that I can see "details" in those
> couple lines showing me playing games....but, oh, is it hard to see the
> bad guys coming up that half of the tube! 8^) 8^) 8^)

        XREF and YREF are the reference voltages for the DACs (In fact,
it's generated BY the DAC-08 (and other stuff,) FOR the AM6012s.) XREF
and YREF should be the same, so you might check that out (although the
reference voltages are not static, they change, based upon the DVY
signals.)

        If you're XREF voltage was bad, I'd doubt you'd get anything out
of the corresponding AM6012 DAC, especially nothing as "good" as a good
half-picture. Generally a reference voltage that's too low will cause
some seriously wierd stuff to happen to DAC outputs -- at least to the
DACs that I build...

> > I sure wish I had an oscilliscope to debug this.... >

        You've got 2 options...buy a scope, or shotgun it. I'd start with
the analog switches if you choose the latter, since they're the cheapest
and easiest to find.

Joe
Received on Mon Dec 1 18:15:53 1997