----- Original Message ----- From: "Ethan Dicks" <firstname.lastname@example.org> To: <email@example.com> Sent: Thursday, May 12, 2011 1:54 PM Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. > On Thu, May 12, 2011 at 1:21 PM, MikeS <firstname.lastname@example.org> wrote: >> Have you tried replacing the video RAM? > > Besides the fact that I did test (and mark) all the 6550s, bad video > RAM is not likely to cause pixel-level defects in the video... that > tends to be a fault around the chargen and attached shift register or > with the timing chain of flip-flops and such. > > -ethan ------- 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? 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. m Message was sent through the cbm-hackers mailing listReceived on 2011-05-12 19:00:08
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