Date   : Tue, 13 Apr 2010 20:27:44 +0100
From   : jumbos.bazzar@... (Mark Haysman)
Subject: Dead beeb - easy tests

> Thanks for the pointer Mark,
>
> I got a 74LS00 and some jump leads and though it's dodgy I can get it to
> boot with the inverter in place.
>
> In Mode 4 I get stripy screen in Mode 7 jumbled characters
>
> It looks to me as if bit 1 is stuck on, I can poke the screen with 
> ?30000=1
> or ?30000=4 to get a dot either side the stripe.
>
> Am I right this is IC62 that is suspect or is it IC54, I'm not really
> following the schematic 100%

Hehe...I always get this bit backwards too, I had it written down on an old 
diagram, which I've subsequently lost!

I *think* it's IC62, which is the one that would be in a socket, if it was 
an upgraded A, this is because it boots in 16K mode, using the non-socketed 
ICs.

You can always try a "piggy" of another RAM chip ontop of the suspect one - 
even if it doesn't cure it, it should change the look of the fault on 
screen.

Mark.