[Coco] CoCo2 lower graphics

[Arthur Flexser]

Very strange.  This happens both with some Rompack cartridges and some
programs loaded from disk?  Consistently with the same programs?  Top half
of the screen looks completely normal?  When you get this, does the program
otherwise continue to run normally, rather than crashing the CoCo?  If the
machine crashes, I'd tend to suspect the 6809.

Art



On Sat, Jun 18, 2016 at 5:08 PM, Michael Pittsley <mikep at twcny.rr.com>
wrote:

> I'm not really sure how to respond to these messages on here.  I hope I
> have
> it right.  Anyhow.  Running screen0,1 goto 10 doesn't do much.  From the TV
> I have the CoCo connected to, it presents an orange line that runs up and
> down the screen until I press break.   I attempted to attach screen shots;
> however they proved to be too large to post on here.
>
>
>
> The CoCo that is having the issue has the XC80652P VDG chip (This chip is
> said to have been pre-release parts).  I reseated this chip and there was
> no
> difference.  I also replaced the VDG chip with a MC6847P chip from another
> CoCo.  Either these two chips are not compatible or the chip from the spare
> parts computer is also broken.  Either way replacing the chip with the one
> I
> had didn't resolve my issue.
>
>
>
> Any suggestions will be appreciated.
>
>
>
> _____________________________________________________
>
> "Michael Pittsley" wrote:
>
> > I have a COCO 2 that when I load certain software or cartridges the
>
> > bottom half the screen is garbled. [...] The garbled graphics is just
>
> > on some graphical games / cartridges.  If I load Tom Mix's Donkey King
>
> > everything works as expected.  Try to run a frogger game or Bridge
>
> > Tutor, I cannot see the bottom half of the screen other than gibberish
> graphics.
>
>
>
> Might be worth a photo of the garbled screen.  The games otherwise seem to
> be running as expected?  Weird failure mode!
>
>
>
> What happens if you type:
>
>
>
> 10 SCREEN0,1
>
> 20 GOTO20
>
> RUN
>
>
>
> ?
>
>
>
> ..ciaran
>
>
>
>
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