DEC M705 vs M7050 in PC05

[Paul Anderson]

A lot of the early unibus boards which were 3 digit and replaced by a 4
digit were duel height boards that required a M7821 and M105 (not sure
about the numbers), and DEC built those into a quad height board and added
a "0".

On Wed, Jul 29, 2015 at 1:56 PM, william degnan <billdegnan at gmail.com>
wrote:

> 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
> >>
> >> 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/M705vsM7050.txt
> >
> > 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
>
>
>
> --
> Bill
> vintagecomputer.net
>