Date   : Thu, 16 Aug 2007 07:39:31 +0100
From   : info@... (Sprow)
Subject: Acquired Beeb with symptoms...

In article <D27938D1A467B04B9D1B16361BA84C970182A8@...>,
   Robert Schmidt-Cisternas <robert@...> wrote:
> I just acquired a Beeb (I haven't owned one since 1986 :-)), and was
> wondering if the following symptoms ring any bells:
>
> - Pressing BREAK once seems to freeze the machine
> - Pressing BREAK a second time seems equivalent to Ctrl+BREAK (or
> power-on?)
> - In general the machine seems sluggish, especially in graphics modes -
> it is not noticeable when typing, but games run much slower than I
> remember them.  For example, the original Repton scrolls at about 2
> frames per second(!)

Sounds like it's spending a lot of time servicing interrupts which aren't
really there. There's a project to do this deliberatly at
 http://www.sprow.co.uk/bbc/buildit.htm
but you don't want this behaviour!

My best bet on no other information would be something wrong with the system
via or decoding of the slow bus nearby. The system via is heavily involved
in interrupts from sources which might not really be there (light pen for
example), it determines whether the last reset was a power on or not, and
also runs some timers.

Try swapping it with the user via temporarily. Also maybe take out the whole
motherboard to check for shorts (washers/paper clips etc) trapped underneath?
Sprow.