9 Apr
2015
9 Apr
'15
11:14 a.m.
On Thu, 9 Apr 2015, Noel Chiappa wrote:
My usual cleaning process for such stuff is to give it a bath in simple
green (either the 1:10 I keep mixed up in spray bottles or 50/50 in a
bucket if the rodent mess is /really/ bad), scrub lightly with a small
nylon bristle brush, and rise. Once clean of the rodent mess, scrub at the
corrosion again with a baking soda and water paste mix and rinse again
with clean water. The cleaning process might well remove some loose
copper, but such traces are going to already be beyond salvage anyway.
There /is/ actually a source for replacement gold fingers (and copper
trace material), but that sort of stuff can get expensive if you need to
replace a lot of them. You might try contacting http://circuitmedic.com/
and see if they have any replacement gold fingers the correct width.
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 about.
Animal urine.
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 washed away.
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 something?