Re: PET 2001 fix Part 3 - RAM/ROM board etc.

From: Ethan Dicks <>
Date: Thu, 12 May 2011 14:50:34 -0400
Message-ID: <>
On Thu, May 12, 2011 at 2:35 PM, MikeS <> wrote:
> AFAIK the old 2001 had the video RAM connected directly to the CG ROM
> (unlike the newer ones which had a latch in between), so if one or more bits
> of the video RAM were unstable (or you had an intermittent socket) which
> caused the data to change part way through a character line, wouldn't you
> then get corrupted characters as the CG switched back and forth?

You could, but in order for that to be stable, it would need to be
synchronized with the pixel clock.  If the symptom was random
pixels/no visible character shapes, I'd be willing to suspect the

> I just thought it'd be an easy and worthwhile thing to try, especially since
> someone on the VCF PET forum just fixed a 'flickering snow' problem by
> replacing one of the video RAMs.

I can see how snow could be an SRAM problem because it's not tied to
the same pixels changing in the same characters in the same way frame
after frame - that is one way I'd expect random addressing of the CG
ROM to manifest itself.


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Received on 2011-05-12 19:00:15

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