Date   : Mon, 15 Aug 2011 22:02:58 +0100
From   : mfirth@... (Michael Firth)
Subject: Advice on restoring a dead Beeb?

On 15/08/2011 00:36, Chris Reece wrote:
> On 15/08/11 09:57, Peter Coghlan wrote:
<snip>
>> The two similar ROMs should have slight variations in what is printed
on them giving clues
>> as to which is which. However, I can't make out the numbers from the photo.
> Yes, that was my problem, too.
>
I'm surprised there isn't a definitive Internet resource with the 
different BBC chip labelling, but Google is failing me for now. I think 
(from looking at a couple of pictures on Chris Whitehead's site and the 
8BS site) the OS 1.2 ROM should end "PB04" and a Basic II ROM should end 
"PB05".

If the incorrect ROM is in the OS socket, you would probably get similar 
results to what you are seeing - the initialisation wouldn't be 
happening, so you'd get no usable screen output, and the sound chip 
would just keep making its uninitialised noise.

On 14/08/2011 21:37, Chris Reece wrote:

<snip>
> I'll establish what the behaviour is with a break-induced reset.  (All
I recall from when I tried it without a logic probe to watch was "nothing
happens" so I'll need to do that again just a little more rigourously.)
>
The first thing to check is that when you press the Break key you can 
see a reset pulse on the reset pin of the 6502. As the break key is 
directly wired to the 6502 reset line, then if the keyboard connector is 
in place correctly and functioning then this should happen.

Hope one of these two points is useful...

Michael