Date   : Fri, 24 Feb 2012 12:19:24 +0100
From   : rick@... (Rick Murray)
Subject: Acorn Electron Repair - Replace 6502 (unlikely)

Hi,

Once came across a Beeb that had a broken CPU in that the maths ops seemed 
to be stuck in BCD mode irrespective of the flag setting. Beeb, naturally, 
failed to start, so at school we cobbled together a test rig on veroboard 
to be controlled by another Beeb's printer/user ports. Many weeks of assing 
around (like you do) and the penny dropped for one of the more mathsy types. 
So a dead-simple boot was written to power up taking account of the BCD maths,
and it worked to spit out a square wave on one of its address lines. Dunno
how or why it would fail in this way, it just did.

If you have time and enjoy experimenting, you could poke around the "dead"
processor. Or... not. :-)


Best wishes,

Rick.

Dave Curran <bbc@...> wrote:

>I've been working on an Electron I picked up at a local flea market.
>'untested' as usual means broken. Blank screen, no signs of life.
>
>After going through all the usual tests, it's turned out to be the 6502
>which had gone. The service manual lists this as 'unlikely', is that still
>the case? I can't remember having this on any of my B's or Electrons, but I
>suppose half a century later it may be more common?
>
>Full story and photos on my blog:
>
>http://tynemouthsoftware.blogspot.com/2012/02/acorn-electron-repair.html
>
>Thanks,
>
>Dave
>
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