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.slyngs...@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
