Date   : Thu, 16 Aug 2007 19:02:22 +0100
From   : info@... (Sprow)
Subject: Acquired Beeb with symptoms...

In article <D27938D1A467B04B9D1B16361BA84C970182A9@...>,
   Robert Schmidt-Cisternas <robert@...> wrote:
> I swapped the two 6522s, with no apparent change.  You say "temporarily"
> - they shouldn't differ in any way, should they?

They're the same, but I (personally) would swap them back if no improvement
is had just so you know you've not made any net change. It might not have
appeared to fix it, but then there might be a secondary fault which needs
fixing first AND THEN swapping the 6522's fixes the overall problem.

Like when a bulb blows when it's controlled by two way lightswitches: always
put the switch back to the original position before changing the bulb!

> I haven't been able to locate any shorts.

Got any test gear? Logic probe? Scope? I maintain that it's the 6502 being
hammered by interrupts which are not really happening - finding where
they're coming from is going to be tricky without any other means of test
other than unplugging chips,
Robert.