Date   : Sat, 13 Aug 2011 18:08:20 +0100 (WET-DST)
From   : BBCMICRO@... (Peter Coghlan)
Subject: Advice on restoring a dead Beeb?

>
>Is there a step-by-step guide for this available?
>

Dunno. I'm just making it up as I go along!
The steps tend to vary slightly depending on what symptoms have
been described and what has already been tried.

>
>There are, IIRC, a number of small gotchas - for example you can't try 
>starting the Beeb without its keyboard, and you can't just pull out the 
>FDC to ensure it isn't that (there's a link to be changed somewhere?).
>

Agreed. I didn't say quite so explicitly but I think I covered both points.

>
>Given the VDU7 bip is optional, I would imagine the "clear sound 
>channels" silences things. This would perhaps narrow the fault down to 
>the VIAs, ACIA (serial) and ADC.
>

I thought there was always a VDU7 beep at power on as this is part of
the "BBC Computer 32K" string being displayed?

>
>Of these, the user VIA, ACIA, and ADC are optional (IIRC the Model A had 
>none of them).
>
>Thus it look like we might be looking at the system VIA as being the 
>source of problem - and the #1 thing here is the keyboard connector 
>itself not being correct and/or corroded.
>

The system VIA itself would seem to be ok as there was no difference
when it was swapped with the user VIA. The keyboard connector is
definately under suspicion, especially if the machine worked before
being bumped around in transit.

It is tempting to try to logically pin down the problem based on
what happens at startup and in what order. However, we don't know
for sure which version of the OS is involved and we are missing some
key symptoms such as what appears on the screen. Because nearly
everything is connected in parallel to the data bus, almost anything
could be the source of the problem, whether it is accessed or not.
Misbehaving memory is another possibility. If some zero page locations
are affected, all sorts of wierd stuff can happen. But, if the machine
worked before shipping and reseating of ICs, the most likely problem
is a bad connection somewhere.

>
>Eh? I thought the left ROM socket was ALWAYS the MOS (extended 
>addressing capability or something), followed by BASIC, followed by 
>three empties for inserting goodies like DNFS, View, and the like.
>

By reconfiguring jumpers, I think it is possible to have the OS in
four parts in what would normally be the paged ROM sockets and have
only one language ROM available in what would normally be the OS socket.
I've never come across this in practice so I wasn't going to mention it
to avoid confusing the issue :-)

Regards,
Peter Coghlan.