23 Apr
2023
23 Apr
'23
5 p.m.
On Apr 23, 2023, at 12:54 PM, Fritz Mueller via cctalk
<cctalk(a)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