16 Feb
2014
16 Feb
'14
5:10 p.m.
On 02/16/2014 12:00 PM, cctalk-request at classiccmp.org wrote:
Subject: PDP-8 core memory troubles
Message-ID:<bsovf9l51pr6bp1098bii2o7nkgmkoiq94 at 4ax.com>
Content-Type: text/plain; charset=us-ascii
Any tips for checking currents/timing? Or should I just replace the
G650, the H219B core stack, or both as a pair? They aren't easy to
find these days and my small chassis only has room for two core boards
that occupy two hex slots each - so they both have to be 16K boards,
as ADVENT requires 32K even though OS/8 runs in 12K:(
Are there any adjustments on the boards? There could be
timing adjustments
or XY drive and inhibit current adjustments. Most of the
old DEC
core systems had a thermistor on the core plane to adjust
select current,
you might compare the two thermistors to see if one has gone
bad.
You could also swap the core planes or other boards to see
if you
could isolate the problem. From the symptoms, though, it sounds
like the problem has to be in either an inhibit driver or a
sense amp
for bit 11, as the XY select is common to all bit planes.
If it was always
the same word, that could be a marginal XY drive current or
a defective
ferrite core, but that is not the symptom you give.
Jon