29 Jul
2015
29 Jul
'15
11:56 a.m.
It could also be the extra "0" is for some reason intended to be
installed in an expansion chassis for the system. It is a stretch to
make this assumption, the thought occured because I know the power
supply in an expansion chassis I have is called h7420a, whereas the
main unit part number is h742a..
On Wed, Jul 29, 2015 at 1:51 PM, Vincent Slyngstad
<v.slyngstad at frontier.com> wrote:
From: Jack Rubin: Wednesday, July 29, 2015 10:08 AM
--
Bill
vintagecomputer.net
If you were following Joerg Hoppe's recent PC05 auction on eBay, you might
have noticed that his system had an M705 in the backplane where I would
have
expected an M7050. This is the way he received it and the restored unit
works
as it should.
Clearly the cards are similar but different but are they interchangeable?
Would the backplane wiring be different and if so where would this be
recorded?
I don't know where to find backplane documentation, but I did at one
time diff the net-lists for some versions of M705 vs M7050. Those
results are paraphrased in
http://svn.so-much-stuff.com/svn/trunk/Eagle/projects/DEC/Mxxx/M7050/M705vs…
The gist of it seems to be that to use an M7050 in an M705 backplane,
BU1 must be high (will probably float high), and BC1 must not be grounded,
New output pins BL2, BT2, and test point AC1 should be unconnected.
A fair chance it will "just work".
Going the other way is probably more difficult, as you'd have to fake
BL2 and BT2 somehow.
Hope that helps!
Vince