21 Feb
2009
21 Feb
'09
4:59 p.m.
Subject: RE: Powering up a 20-year old MicroVAX II
From: <arcarlini at iee.org>
Date: Sat, 21 Feb 2009 22:04:43 +0000
To: "'General Discussion: On-Topic and Off-Topic Posts'" <cctalk
at classiccmp.org>
cctalk-bounces at classiccmp.org wrote:
Correct the worng harness has unequal length wires and the correct
one has equal length wires. The harness in question goes from the
Backplane to the PS.
The problem is with unequal length wires the connectors were sharing the
load unequaly and the connecotr would overheat and fail sequentially.
It was more of a problem on highly loaded boxes.
IMHO the most important thing to do after
checking for
obvious problems
-- loose parts, evidence of overheating/burning, etc, is to test the
power supply (PSU) on a dummy load. A defective PSU could
wipe out every
chip in the machine!.
In addition, pay particular attention to the PSU wiring harness.
The early rev of harness on (iirc) the BA23 had a habit of
catching light. I think it was slightly underrated for the
maximum power load and so would deteriorate over time. It
would eventually reach the point where one of the N conductors
would fail, leaving N-1 carrying way too much load and smoke
ensued.
Field service were (again, iirc) supposed to swap these
out if
they came across them. But if your machine has truly not been used
for twenty years, it ended up in storage relatively eraly in its
life and so may not have had a chance for some FS TLC.
20 years is maybe on the wire. It may have been already replaced.
A little bit of googling should find you the relevant details
(or you could wait for the next post which will no doubt be
from someone with much better memory than me :-)).
The only other thing I would add to Tony's post is that once
you think it isn't going to fry your boards (or burst into flames)
then you only need the CPU and one memory board in. Then you hook
up a terminal to the console (9600-8-N), set the switch properly
and check that you get some kind of life on the console.
It doesnt bust into flames, it can overheat to the extent of
destroying the connectors and smoke some.
In this day and age cookingthe backplane connector is a real pain
as spares are getting scarce.
Allison
At that point you can start to add the remaining boards
(checking
that Qbus grant continuity is OK as you go) and build your system
back up again.
There are plenty of docs you can track down on Manx
(http:://vt100.net/manx).
You can google for the various Micronotes too, some of them are relevant
to the MicroVAX, others to the Qbus, and all of them are interesting
background reading.
Antonio
arcarlini at iee.org