1 Jun
2010
1 Jun
'10
10:57 a.m.
>(tony)
Have you read the report in Computer
Resurextion? (This is the _only_
indformation I have seen on this project). There were a couple of
things
that really upset me...
=20 tty much verbatim. What do you find upsetting?
=20
I don't have the appropriate copy of Computer Resurection to hand, but
from what I recall it said something like (this is a paraphrase, but I
hope I've kept the meaning)
'After basic electircal safety tests we applied power and the machine
appeared to start up correctly'
'However one part proved unreliable, we replaced all the PCBs, but it was
still unreliavly. In the end we discovered the power supply was faulty,
so we replaced that' ... etc
<<<<
The article is online at
http://www.cs.man.ac.uk/CCS/res/res48.htm#e It is worth rereading to correct your memories
It shows that a great deal of care was taken in the process.
I;ve read it, and I agree that I had misremembered some details. However,
I feel my 2 major commetns still stand -- that not enough checking was
done (or at least it's not recorded as being done) before the machine was
powered up, andthat a PSU was swapped out when it should have beeen
repeiared (to keep the machine as origianl aas possible)
A minor comment. If this PDP11 is like most of the more recent models
that I've worked on, then eorrr code 77 doesn't mean a PSU failur. What
it meansis that the CPU hasn';t tried to write to the error display
latch. This could be because the PSU hasn't deasserted DCLO (I think,
maybe ACLO), it might be because the CPU isnt; clocking, or has failed
trotally. Inb otehr words, to me, it would indicate I should stick some
test gear on the DCLO (and ACLO?) lines, then if they're OK, strt
debuggihnthe CPU board, and if they're not, dive into the PSU.
There is, in any case, an important difference between attempting to restart
equipment that had apparently been operational only a few months earlier
before it was moved - in which case normal field-service procedures seem
I disagree. It's entirely possible for somethign to break loose in
shipment and cause damage when the machine is powered up again. With some
PSUs desgins (I doubt the one in this machine is like that), jsut one dry
joint openign up can ruin every IC in the machine.
Just about every year I cart one of my HP desktop machines to the HPCC
mini-conference.. And although I have been running it in my workshop the
night before the first thing I do when I get it ot the meeting is test
the PSU on a dummy load. I'd rather have to fix the PSU than have to fx
the PSU _and replace most of the logic chips_.
perfectly adequate* - and something that had been
stored for years which
might need treating as requiring the sort of investigation and testing that
would be associated with rebuilding.
* It is the experience, and thus training, of field-service organisations
that a strip-down and rebuild procedure is more likely to introduce faults
than to locate them with any reasonably modern equipment (and, in this
context, PDP11/84s can be considered "reasonably modern"); This all changes,
of course, if power-off time has been sufficient for power-supply faults to
become likely.
This has not been my experience at all. I have never had any problems
dismantling and reassembling a machine. And I take my machines apart a
lot more than most people would (since I demonstrate them to friends, etc
and I _always_ take them apart to explain the internals).
I also would claim that field service repairs and museum restorations are
totally different things (if only because field service cna genrrally get
any new parts they need, museums cannot). I would question that field
service people are necessarily the best people to do museum restorations
(as you seem to imply). There will be some that are, sure. And there will
be some that just follow the CE manual and are completely helpless when
they don't ahve a swap kit to hand. I don;t beleive there's any
correleation between ability to repair a machine, and whether or not you
work(ed) for the manufactuer a a field serviceman.
-tony