28 Sep
2014
28 Sep
'14
11:33 a.m.
Date: Sat, 27 Sep 2014 22:11:52 +0100 (BST)
From: ard at p850ug1.demon.co.uk (Tony Duell)
To: cctalk at classiccmp.org
Subject: Re: Further PDP-11/05 debugging -- core memory faults
Message-ID: <m1XXzHa-000J4dC at p850ug1>
Content-Type: text/plain
It's possible to replace a wire in a core mat, I have made it myself in a
core pack that belongs to a PDP-8/L. Depending on the sizes of the cores
it migth be more (or even much more) difficult. If the wire is broken
outside the mat, it?s possible to extend the broken wire a bit and put in
a new piece of "fresh" thread. I used a good stereoscopic microscope which
essentially made it possible. You also need some time and a steady hand.
Further investigation reveals that the connection between FD1 on the
card edge connector (the XS05 signal) and pin 7 of the 2501 at E22 is
broken. This, I believe, is a matrix wire (or "magnet wire" from the
engineering drawings) meaning that I've got a broken wire somewhere in
the core mat.
I would just trace the tracks, both visually an with an ohmmeter, from
the edge conector pin to the core mat and from the core mat to the diode
array. Just in case.
Incidneatlly, no matter what it says on the cover over the core mat, you
can take it off quite easily without damage. Just don't drop it on the
corse.
If it is the core address wire in the mat, you may have big problems.
Some of these mats had the cores cast onto the array of wires, no
pre-made cores that were threaded with the wires. In which case,
replacing the wire might be impossible.
My first throught was 'have a go anyway. If you wreck the board, well, it
doesn't work now'. And then I thoguth that no, you should treat it with
care. Even if you don't have the skill to fix it now, you might do so i
nthe future. Or somebody else might have a go. In any case, you don't
want ot make thigns worse.
-tony
I do agree upon that. The worst thing that could happen is if you crush a
core...
/Anders