Altair Turnkey and some DEC stuff cheap
jnc at mercury.lcs.mit.edu
Thu Apr 9 07:49:11 CDT 2015
> From: Bill Degnan
> These are best for someone who has experience cleaning a "barn find"
> * items contains/contained a rodent nest.
Those who missed out on this deal may find this sequel comforting.
There was one aspect of this (which Bill alluded to somewhat eliptically -
perhaps out of delicacy, or perhaps he assumed that anyone who'd done one of
these would already realize the full implications :-), but which didn't
really impress itself upon me until I started the ride home - at which point
I started to get olfactory clues. Yep, some of you know what I'm talking
Of the three boxes, one (the '11/44' - it was actually just a BA11-K) was
totally sodden inside (those nests are basically giant sponges), and one of
the 11/34's was half-sodden. The thing about animal urine that's really a
problem is not the smell, or the mess - it's that it's _incredibly_ corrosive.
>From the condition of a couple of the cards which had gotten the worst, I
think there was actually some galvanic activity between the copper traces,
and something else - maybe the iron in the chassis? Traces were quite
literally eaten right off the cards. You can see the trace heading towards
one of the gold-plated contact fingers, and then - poof! - it disappears.
Dozens of traces on those two cards have big gaps in them.
Although now that I think about it, it couldn't have been galvanic activity
which dissolved the copper in the traces; if I remember my inorganic chem
correctly, iron is above copper on the galvanic activity scale. But anyway,
Also, totally amazingly, quite a few of the gold-plated contact fingers also
have damage! One is quite bad - although luckily I think there's a patch left
where the contact would be, so that can probably be saved. Whatever was going
on must have eaten the copper out from underneath, and then the gold just
So I think all those traces can be repaired, if there's ever a use for that
interface (an RH11). Just a lot of wires to solder in....
The other problem is the backplanes. DEC boxes put the backplanes at the
bottom, so these nests were resting on the backplanes. Having cleaned them off
(well, stage 1 cleaning), I _think_ that, amazingly enough, the contact pins
are OK. (Now that I think about it, they are tin-plated - so there's the other
end of the galvanic activity. Ah, well, better to eat the traces than the
contact pins - those would be almost _impossible_ to repair.)
The real problem is that there's 'grup' (a Dave Clark neologism) in the thin
space between the plastic contact pin housing blocks and the PCB. Needless to
say, one can't take the PCB off to get in there...
So my plan of action is to stick them in water for a couple of days, and
then use a water jet to try and get down in the thin gap between the contact
blocks and the PCB, to clean it out.
Does this sound OK? I can't think of a reason why immersing a backplane in
fresh water for a couple of days would do it any harm, but maybe I'm missing
I just think it's critical to recovering these to get as much out of that
area as I possibly can. If an open develops somehow, well, that can easily be
fixed with a wire. But a short.... you're screwed.
Moral of the story: if you're going to store your antique computers in a barn
- make sure to keep the rodents out!
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