PDP-11/35: Disgusting, Nasty, Dirty Unibus Backplanes

Published Sunday, June 10 2012

Tonight I moved on to a task I’ve been dreading: cleaning up the Unibus backplanes.

Electrically, they seem like they were probably in acceptable shape, but they are incredibly filthy. They were exposed to the elements in a shed for many years, face up and just waiting for God knows what to fall or crawl into them. The slots that did not have cards had become embedded with bits of fiberglass, dirt, spider webs, insect droppings, and probably a goodly dose of mouse piss. Some of the individual nooks and crannies (I don’t know the technical term here - the individual slot openings where a single finger of one card edge connection is installed) had what I assume were insect or spider egg sacs in them, gripping the sides tightly.

All in all, I spent about an hour and a half on just one backplane, the four-slot DD11-A. My method for cleaning involved using a vacuum cleaner, a stiff-bristled brush, and a variety of toothpicks to get into the slots and worry out all the junk. Some of it was quite sticky and hard to get out. Spider and cobweb debris, I assume? It felt like it took forever, brushing, picking, vacuuming, brushing, picking, vacuuming…

When I felt like it just wasn’t going to get any cleaner and all of the obvious bits and pieces had come out, I gave the whole thing a healthy dose of Deoxit contact cleaner spray, and worked a bus terminator card (dual height) gently in and out of the slots to clean the contacts. It looks pretty clean now. Maybe not “good as new”, but less likely to cause a gag reflex at least.