On 2023/04/23 10:00 a.m., Paul Koning via cctalk wrote:
On Apr 23, 2023, at 12:54 PM, Fritz Mueller via cctalk <cctalk@classiccmp.org>
wrote:
Hi folks,
I’ve been picking my way through a PDP-8/L restoration lately. I’ve found that
everything in the machine is covered with a uniform layer of dark “soot”
(enough to blacken your hands while working with it) which I would like to
clean up. Perhaps the “soot” is actually from a decomposed air filter, as I
don’t imagine this machine was operated in a smoky environment, and there is no
smoke odor.
I usually use 99 IPA and cleanroom wipes for spot cleaning these sorts of
things, but in this case there is so much of it that I feel that would just
push the soot around rather than clean it off. I think some sort of actual
rinse would be needed here.
I’ve been eying the dishwasher, for the subset of flip chips that that are just
DIP logic, carbon comp resistors, and ceramic bypass caps, anyway. But I
haven’t been brave enough to try that yet... Most of the logic here has date
codes to ’68 or ’69, so I’m inclined to treat it gently. Any suggestions for
approaches to clean this up?
Dish washer soap may be caustic. Detergent for washing dishes by hand may be a
better choice.
Follow-on question: the majority of the legs on these old DIPs are showing what
I’d call “moderate” corrosion — nothing looks like it is in danger of being
eaten all the way through, but the process is underway. I was wondering if
something like a light shellac or other inhibitor could be brushed over these
pins to at least slow their inevitable demise?
I wonder if you might be seeing corrosion caused by leftover flux. Modern flux can be of the "water
soluble" kind, which indeed washes away nicely with warm water; I've used that for surface mount
projects. The traditional flux is rosin flux. That can be removed with a solvent but that wasn't
necessarily done. Amateur project built with that typically would not be cleaned, and that was generally
considered ok. A bit like modern "no clean" flux. But flux is somewhat corrosive, and "no
clean" may mean simply that it's not an issue within the life expectancy of the device. So -- you might
see if rosin flux remover does anything.
paul
I use Dow Corning #4 Dialectic Grease to reduce or prevent corrosion on
power and signal connectors. Read the spec sheets on that stuff, it is
really good for metal on metal connections. I imagine it would work well
on those silver alloy IC legs that are gradually oxidizing away...
John :-#)#
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