Norsk Data Nord-10/S restoration effort on the way!

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Nov 14 17:13:49 2004

> > Which is 11 years ago....
> At the very most 11 years ago, which still isn't bad.

I check the PSUs of machines that I own and have run before if I've not
powered them up for, say, a year oe more.... It doesn't take long to do
(especially not if you're familiar with the machine and/or have
schematics), putting right the damage can take a lot of time and money.

Most of the time you'll have no problems, sure. Most of the time when I
get a machine on the bench (wheter a 'new toy' or something from my
existing collection), the PSUs behave perfectly on dummy load. But if
something does got wrong, you really don't want to kill all the chips....

There is anotehr issue, actually. PSU problems -- marginally low
votlages, ripple, and so on, can cause all sorts of odd behaviour that
will take hours to find if you don't initially suspect the PSU (like the
time my PDP11/45 would run for 1botu an hour and a half before falling
over in all sorts of odd ways -- I traced that to a '+5V' supply to the
memory that was actually about +4.6V). Checking out the PSUs can
eliminate such problems.

> I think it suffices to say that the guy who cut his teeth on the machine
> and has supported them since 1986, and *owned the company since 1992*
> didn't have any problems with it... He said that the PSUs were sturdy

That would not be enough for me. Heck, the assurance of the designer
wouldn't be enough for me (and nor, for that matter, would anybody else's
assurance). The risk is just too great.

Sure the PSU will have built-in protection -- all decent machines do
(although HP omitted it from their desktop calculators for some unknown
reason -- the HP9815, 9825, 9832, etc desparately need a crowbar!).But
I'd rather not rely on it. Better to be safe than sorry.

> I may have been mistaken, but at the time, as presently, I didn't see
> the need to delve deeper into the PSU.

All you need to do is disconnect the PSU from the machine, connect it to
dummy loads (car bulbs are what I noramlly use -- 6V ones on the +5V
line, for example) and check the output voltages. You don't need to
investigate the internals of the PSU unless there's something wrong.

-tony
Received on Sun Nov 14 2004 - 17:13:49 GMT