RE: Troubleshooting

So if I have a Battle Zone board (notice a pattern yet? :) with a problem
at the first amp out from the DAC and I want to check the DAC output with
my scope.

I guess that I can't just go into XY mode on the scope and check the DAC
output.

So how would I check to make sure that is OK short of breadboarding a TL082
and using that to check my outputs?

David
> ----------
> From: Clay Cowgill[SMTP:clayc@diamondmm.com]
> Reply To: vectorlist@spies.com
> Sent: Monday, January 19, 1998 4:15 PM
> To: vectorlist@spies.com
> Cc: Clay Cowgill
> Subject: Re: Troubleshooting
>
> >> Can someone confirm or deny that the DACs in Atari color games, let's
> >> say Star Wars at least, are setup to produce a change in "current"
> >> rather than a change in "voltage" at their output?
> >
> >Yes. I recall seeing that in 1 or 2 schematics. The DAC outputs a current
> >which is then fed to an OP-Amp to get a voltage. It's important to
> >have a voltage, as that's what matters to the analog switch...
>
> Paul's right. Atari uses current output DACs.
>
> >As I recall, the output of the DAC is not the beam position, but rather
> >the velocity. To get beam position, there is another op-amp configured
> >as an integrator - apply the "velocity" voltage and the position responds
> [...]
> >in signals from somewhere else - like a cinematronics game - if you feed
> >them in at that point, you get to use the Atari pincousion stuff. Just a
> >thought...
> >
> >This is all from memory, so there may be something in error. Can anyone
> >think of a correction?
>
> Right, Atari used the LF13201 analog switches to short the integrator caps
> resulting in a "return to center of screen" action for the AVG based
> systems (like Star Wars). Like Paul said, the analog switches were also
> used to route the voltage output through another inverting amplifier to
> produce a screen "flip" for the cocktail games.
>
> On older DVG based games (like Asteroids), the analog switches were not
> needed for integrator control (the vectors were directly generated by the
> DVG), but were instead used for "cocktail flip" as described above.
>
> Kind-of interesting to note that Atari would leave a lot of things
> "unpopulated" on some boards (presumably to cut costs), but never bothered
> to customize loading options for the PCB's for non-cocktail versions of
> the
> vector games... (I'd have to guess that they mostly shipped uprights, so
> it seems odd to burden the volume shipper with extra hardware costs...)
>
> -Clay
>
> Clayton N. Cowgill Engineering Manager
> _______________________________________________________________________
> /\ Diamond Multimedia Systems, Inc. clay@supra.com
> \/ Communications Division http://www.supra.com/
>
>
Received on Mon Jan 19 16:48:23 1998