Date : Wed, 01 Nov 2006 11:34:57 -0600
From : julesrichardsonuk@... (Jules Richardson)
Subject: nutso keyboard decoding
Whilst talking about sick beebs...
Has anyone ever come across a beeb fault where keyboard decoding was
completely messed up? Witchy over at Binary Dinosaurs has one (a model B)
where the key which appears on screen hardly ever matches the key actually
pressed, which is something of an odd fault!
We had another healthy beeb nearby (but no manuals or other tools) so tried
the obvious 'quick fixes' - swapped keyboards, swapped ROMs (OS and BASIC),
swapped 6522 chips, swapped CPUs, checked for obvious 'hot RAM', reseated
anything that was socketed, checked under the PCB for invading metallic debris
etc. but with no luck.
This was a couple of months ago, but I'm pretty sure I forgot to post about it
to the list :-) Unfortunately it also means my memory isn't perfectly sharp -
but recollection is that:
Usually a few displayed letters would match what was actually pressed, but
most keys produced incorrect results.
The keyboard generally seemed a little 'sluggish' in response.
Results varied between power cycles and weren't always consistent.
Is that a fault that anyone's come across before? Other than a Master that I
have which transposes X, C and V I've not seen or heard of anything like it
before. The fact that it otherwise boots up OK at least seems to indicate that
memory and address decoding is reasonably happy. It's almost as though
something was screwing up the data bus, but if that was the case I'm surprised
the machine would ever get to a prompt...
If you've ever wondered how you get triangles from a cow
You need buttermilk and cheese, and an equilateral chainsaw