Re: Looking for DECstation 3100/2100 or DECsystem 5100

[Felix Deichmann <m4j0rd0m0%gmail.com@localhost>]

2017-08-14 1:37 GMT+02:00 Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>:
> I replaced my 5000/125 PSU with ATX one, based on info of this page:
>  http://www.xanthos.se/~joachim/DS-ATX.html

:)

> (though I don't know PSU pinout for 3100 ones)

FWIW, this is harder to do for the DS3100 (but still possible). The
DS3100 KN01-AA board and H7821 PSU use a 14-pos. Molex Mini-Fit Jr.
(an "ATX 14-pos. variant" connector if you want) with the following
pin-out:

1   -12V    (blue)
2   GND     (black)
3   GND     (black)
4   GND     (black)
5   +5.1V   (red)
6   +5.1V   (red)
7   PWROK   (brown)
8   +5.1V   (red)
9   +12V    (orange)
10  +5.1V   (red)
11  GND     (black)
12  GND     (black)
13  -9V     (yellow)    \  probably
14  -9V ret (white)     /  isolated!

PWROK is active-high (5V logic) and thus directly compatible with the
ATX PWROK output. The power rails referenced to GND (excluding -9V)
should also be compatible. The hard part is deriving a probably
*isolated* -9V rail for which no ATX equivalent exists! I think this
is used for 10BASE2 ethernet. So re-using a 5V-->9V isolated DC/DC
converter from an old BNC network card could do the trick (tip from
http://www.sprut.de/electronic/switch/smallup/smallup.html#5vto9v).

As with all old systems, they heavily load the 5V rail. You will
ideally use an old ATX PSU for that (pre-Pentium4!), because the
modern ATX12V variants, as the name says, probably do not provide
enough power on the 5V rail, could get out of balance etc.

However, most VAXstations 3100 also use the H7821, so it could be
easier to find one there before starting to tinker...

Felix