Date   : Wed, 18 May 2005 13:56:34 +1200
From   : Michael Foot <mjfoot@...>
Subject: Re: RAM chips for Model B

In message <1115931071.4283c1bf13a10@...> you wrote:

> Quoting Sprow <info@...>:
> 
> > In article <1f29d5694d%mjfoot@...>,

> > 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!
> 
> Good point. I'd just assumed it was the RAM since MODE 0 is partially correct 
> and it works when in 16K mode. I check that IC.

I've since replaced IC39 with a 74LS283 and it hasn't fixed a thing. Shame. 
Half of the memory ICs are socketed and so I've swapped them all around 
but I still have the same problem. In Mode 7 I get a left bracket ( showing
in each character space with a few other random dots. This does looks like
a whole address line is faulty somewhere.
Will touching each RAM chip to see which one is not warm tell me which is
faulty? I still don't know which one is the video memory.

> > Alternatively, I think I have some spare RAMs somewhere,
> 
> I'll let you know if I need them. Do you know which RAM chips are mapped to 
> the video memory space?

I might need to do this. I'll search my other beebs and see if any of them
have socketed RAM I can borrow first though.

Cheers,

Mike.

-- 
Michael Foot <mjfoot(at)paradise(dot)net(dot)nz> *
http://homepages.paradise.net.nz/mjfoot/
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