I won't say you're alone there, but I've more often than not seen people,
particularly people paid to do this sort of thing, isolate faults to the board
level by swapping boards, then sending the board off for depot repair. I guess
if you don't mind that the machine is down until the board is fixed then it
doesn't matter, but if that's the case, the machine isn't that important.
Having spares of everything is a strategy for keeping a system running. It may
not be the most sophisticated, but it is a strategy that ensures minimal
downtime. When I was working in the aerospace industry, it was not unusual for
a system to have two spares of everything on site, just to ensure that the
system could be kept running as much of the time as possible. In many cases
this was very difficult to do, since various system revisions had to match the
board spares, and the replacements had to be exact. If you didn't want to wait
for replacement parts, though, the only option was to buy them in advance.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, June 11, 2001 2:38 PM
Subject: Re: Ebay horror ...
> > Unfortunately, it's often necessary to sacrifice one potentially repairable
> > machine in order to repair another. I have no patience for those who
poo-poo
> > that notion. Where do they think those replacement boards, no longer
> > manufactured since sometime a couple of decades back, come from?
>
> Yes, but most of the time you don't need spare boards (or any other
> complete modules). The only time I would need a complete PCB is if one
> was missing, or had caught fire, or something. I've never 'repaired' a
> computer (or anything else for that matter) by swapping boards, and I
> don't intend to start now.
>
> Most of the time, the parts I need to repair the sort of machines I am
> interested in (PDP8s, PDP11s, PERQs, the older microcomputers) are things
> like transistors, TTL chips, common microprocessors and support devices,
> and so on. Parts that I can still buy new with no problems. And I'd
> rather use those than strip another machine to get them.
>
> There are exceptions, sure, but they're not that common.
>
> [...]
>
> > Would you, Tony, store an old IBM box that required 440-Volt 3-phase power,
and
> > was missing a 48" disk drive without which it had little hope of working,
and
> > without any notion of where to get software?
>
> If I didn't already have little enough floor space, sure. 3 phase mains
> is not impossible to get (it's not cheap, but it is _possible_), and there
> is probably some way to get round the missing peripherals.
>
> Heck, my first minicomputer was roughly in that state. OK, it only needed
> normal single-phase 240V mains, but there were no peripherals, no
> documentation on the peripheral interfaces, and no software. I did have
> the instruction set manual, and the schematics of the CPU, but that was
> it. Together with a couple of friends we got it working.
>
> That was 15 years ago. I've learnt a lot since then. I would certainly
> consider any machine that could _possibly_ be got working (i.e. it's
> complete enough to have at least the entire processor, or some chance of
> getting the processor parts).
>
> -tony
>
>
Received on Tue Jun 12 2001 - 04:07:30 BST