Date : Mon, 03 Feb 2014 07:46:17 +0000
From : bbc@... (Dave Curran)
Subject: Problems with BBC Micro
If it isn't a ULA fault, it could still be the memory. 30 year old DRAMs
are often a problem on Spectrums and Commodore 64s, although I don't recall
seeing it very often on BBCs.
Depending on how sophisticated the RAM test you ran was, it may not have
checked the areas reserved for screen RAM, which is potentially where the
problem is.
Do any of the 4816 DRAM chips feel warm to the touch?
Thanks,
Dave
On 2 February 2014 23:51, Daniel Beardsmore <public@...> wrote:
> What issue is it?
>
> Early issues (at least up to 4) used a Ferranti ULA for the video
> controller chip, and they got hot and committed acts of permanent
> self-harm. The chip never burnt out, but you'd see all sorts of weird
> artefacts that would be consistently present forever. My first Beeb would
> draw yellow as red in MODE 2 unless you remapped the palette, and whichever
> mode Codename: Droid ran in (1?), would show stripy colours under certain
> palette assignments. It was like this for the three years I owned it.
>
> The Ferranti video ULA was the only chip with a heatsink, and the video
> chip is located just behind the OS ROM.
>
> If this chip says "VTi" on it and it has no heatsink, it's the replacement
> ROM.
>
> You *can* put the newer VTi chip in there -- I've done this a couple of
> times, but it may break MODE 7 output under UHF (that's what I saw when I
> tried it on one computer; in the other instance, I was using a monitor).
>
>
> Just a guess, but it's one common cause of weird video issues.
>
>
>
> On 2014-02-02 23:17, Chris Osborn wrote:
> > Trying to figure out what might be wrong with my BBC Micro. When I go
> into Mode 0 and hit return a bunch, the screen freaks out and does this:
> >
> > http://i.imgur.com/qxrNCRQ.jpg
> >
> > The computer doesn't crash, I can still type and switch modes and
> things. I found a type-in BASIC program that did a simple RAM test, and it
> didn't find anything wrong. I don't have any other BBC Micros available to
> me, so it's hard to try swapping parts around to narrow it down.
> >
> > Has anyone seen anything like this before and might know how to fix it?
> >
> >
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> >
>
>