hams on classiccmp
pat at computer-refuge.org
Sat Jan 17 14:06:40 CST 2009
> From: brad at heeltoe.com [brad at heeltoe.com]
> Ian King wrote:
> >I just got a VAX-11/780-5 up with VMS on TCP/IP....
> very nice. Can you describe how it went? Was the 780 previously
> in moth balls?
On Saturday 17 January 2009, Ian King wrote:
> This machine was one of a pair bought from a collector who bought
> from a collector who bought from...? It was interesting noting the
> differences between the two: for instance, on one the black foam was
> in fairly good shape (replaced it anyway), but on the other it was
> falling off in chunks. Both seemed in good mechanical condition.
> The next step was to ensure electrical integrity.
FWIW, if you can be sure you're going to operate the machine in a
relatively clean environment (eg, no carpeting or other things to
generate dust), I'd forgo the filter foam, as all it'll do is crumble
and block airflow.
> So I replaced every electrolytic capacitor of consequence in the
> switching power supplies - five in one machine, six in the other -
> plus the LSI-11 boot machine and RX01 boot floppy. This was
This also seems unnecessary if the capacitors were still good. The
11/780 I got up and running has one bad psu (de-asserts DCOK every once
in a while, and causes the machine to reboot) which may be bad
capacitors, but everything else was ok, despite being stored for over
> After all of this, we carefully brought up the machine. We had a
> challenge because 120V three phase doesn't seem to be usual practice
> in US wiring - we had 240V three phase, but that obviously wasn't
> going to do us any good! Carefully looking through the power
> distribution unit's engineering drawings, it became clear that DEC
> used three-phase simply to balance the current load among the legs -
> in fact, everything runs on 120V. So we used equal care in reviewing
> the wiring of the warehouse where we keep these machines and found
> three outlets that were (a) on the same side of the 240V mains and
> (b) not sharing a breaker and circuit. Those were connected to a
> three-phase outlet, the VAXen were plugged in and voila! NOTE: we
> have a team member experienced with commercial power circuits. Don't
> try this at home - or if you do, be very very careful and be certain
> that, from any of the three live blades to another, you don't have
> more than 120V.
First, I want to point out that all of the power outlets on the PDU are
120V, 20A (NEMA 5-20R) outlets, so it should be somewhat obvious from
that, that the machine doesn't need three phase power to run, no
engineering drawings required. :)
Also, your statements about three phase power aren't quite valid. You
may have had three-phase 240V, but that is unlikely, the typical
practice in the US for non-motor loads (lighting, general power usage)
is 120/208V three phase or 120/240V single phase. In normal use, the
three phase connections on the VAX PDU have 208V between them, and 120V
to ground, which is a standard 120/208V three phase system.
You can run the machine off of single phase power by chosing up to three
separate 120V circuits - it's ok if they're on different phases, having
240V phase-to-phase is OK - and running each one to a different phase,
and tying all the neutrals together to the neutral in the machine. In
fact, it is a good idea to make sure that you have different phases, so
that you minimize the neutral current, otherwise you may end up with
melted wiring or fire, and selecting opposite phases will do this for
you, as the netural current from opposite phases will cancel either
Fortunately, an 11/780 doesn't draw nearly the outlet/PDU rating; I
think I measured around 24A total draw at 120V from all three phases on
mine, and load didn't raise that too much. I've run it from three 15A
circuits (in a building with 120/208V power that I'm not allowed to put
in my own outlet for it ;), and it was ok, each phase was around 8A
> Now that the machines would power up, I scoped all the power supply
> voltages to ensure they were really DC, i.e. that I hadn't missed an
> important filter cap anywhere. All good, so I tried booting from the
> floppies we got with the machines.
Fun. I'd suggest putting a scope (or even better a one-shot that
triggers when they go off) "DCOK" and "ACOK" outputs from the PSUs as
more important; checking voltages with a DMM is probably more useful.
> I was able to get the basic
> console to boot - hooray! - but was unable to get the
> microdiagnostics to run. We had agreed that successful execution of
> the low-level diagnostics was a precursor to any attempt to install
> the OS, so this was a roadblock.
Your OS is probably the best diagnostic that you have. If it doesn't
boot, or crashes, there's something wrong, which you can pick a precise
diagnostic to examine the problem. Diagnostics sometimes find problems
that don't really exist, and miss things that are show-stoppers.
> We had CDROM media for OpenVMS 6.2, the latest version certified for
> the VAX-11/785
7.x works fine.
> Now we were cooking with gas. I had a valid VMS license but not a
> UCX license.
You should be able to use the hobbyist license, unless you're planning
on running the machine commercially.
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