> 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
