[Coco] FW: CoCo2 lower graphics

Michael Pittsley mikep at twcny.rr.com
Mon Jun 20 19:12:53 EDT 2016

That was it.  Swapping out the SAM chip did the trick.  I had to replace the
SN74LS785N with a SN74LS783 chip.  But so far everything seems to be running
as it should.   Thank you a bunch for the quick responses.


-          Mike


-----Original Message-----

Date: Sun, 19 Jun 2016 07:33:11 +0100

From: Ciaran Anscomb <cocomalt at 6809.org.uk <mailto:cocomalt at 6809.org.uk> >

To: coco at maltedmedia.com <mailto:coco at maltedmedia.com> 

Subject: Re: [Coco] FW:  CoCo2 lower graphics

Message-ID: <17321.1466317991 at candle.6809.org.uk
<mailto:17321.1466317991 at candle.6809.org.uk> >

Content-Type: text/plain; charset="us-ascii"


"Michael Pittsley" wrote:

> I was unable to send this to the group due to the attachments being too

> large.   Any additional assistance you could give would be grateful.


Hope you don't mind, I'll reply to the list, and have uploaded the jpegs




> 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.  Attached see 

> the screen shots or what I am talking about  the lower / bottom half the
graphics not working.


So to me the Frogger shot looks like a low-res mode is being presented as
hi-res.  The VDG itself doesn't do this, it's the SAM that handles the
addressing, so if possible I'd try replacing that chip (6883,

SN74LS783/5) - everything else the SAM does looks like it's working so I'd
guess at some internal fault just limited to the video address counters or
divisor selection.





-          Michael Pittsley

-          315.436.9966


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