Date   : Thu, 12 May 2005 19:23:14 +0100
From   : Sprow <info@...>
Subject: Re: RAM chips for Model B

In article <1f29d5694d%mjfoot@...>,
   Michael Foot <mjfoot@...> wrote:
> I've just got hold of an Issue 3 Model B. Functionally it works apart from 
> the screen being a mess in all modes. In MODE 7, there is vertical lines 
> everywhere and the text is not readable. In MODE 0, the top third of the 
> screen is fine and the bottom part contains random dots. If I shift the 
> jumper to make it use just 16K, then all is fine. I'm assuming 1 or more 
> RAM chips are faulty, but which ones? Which RAM chips are used for video 
> memory and where can I get replacement ICs from?

You sure it's the RAM and not the address multiplexing? I had a similar
sounding problem on a machine which was fixed by replacing IC39 (74LS283)
which I sat looking at with a scope and saw it couldn't add up!

Alternatively, I think I have some spare RAMs somewhere,
Sprow.