[cctalk] Re: flipchip cleaning and pin corrosion inhibition

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? 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 did purchase and build out one of Vince’s flip chip tester kits, and have found it super useful for this project. Of the large percentage modules that have test vectors supplied, most have tested fine. Three M216 flip-flop modules and one M113 nand module were flagged for repairs this way. Advice appreciated, as always! cheers, —FritzM.