Solving an old surplus mystery

Several years ago, we came across this interesting artifact at one of our local electronics surplus shops, and couldn't really make heads or tails of it. But after the passage of the aforementioned several years-- along with several dozen interesting suggestions from our readers --we haven't been able to get much closer to an answer.

But then, at this month's Electronics Flea Market, we came across what appears to be a related chunk of hardware:

While we do not have the original "artifact," the thickness and hole size of this new board are reasonably consistent with that of the other board. Certainly, the layout pattern is the same, suggesting that they serve the same purpose, if maybe not the same brand or manufacturer.

The visible markings on the different sides of the board are as follows: Chassis series No 62800 #279, 24930-101916-5, AMP-53, AMP 397503-4 8128. Amp is the manufacturer (they still exist, as a brand of TE Connectivity), and 8128 (week 28 of 1981) appears to be the date code.

The elements installed on the board-- clearly some kind of electronic patchboard --come in a few different varieties. First, there are binding posts, anchored semipermanently into certain locations, with electronic components such as resistors, capacitors, and permanent wiring, soldered between them. There are also movable "patch" cables (the ones with the plastic rings on the ends) that can be moved from point to point.

Here's what one of the movable patch cables looks like: just a single insulated conductor, that snaps into place.

Every binding post and cable inserted from the top sticks all the way down through the bottom, with a gold plug showing through on the other side. The blue patchboard itself is just a passive chunk of plastic-- there's no internal wiring. So it's clear that this whole assembly itself actually plugs into something else: some kind of backplane that connects the electronics together in a prescribed manner, and can be reconfigured with the movable patch cables.

If you look a little closer at the back, you might notice that the holes appear to be D-shaped. It turns out that the hole is circular until the very bottom, where there's just that little lip on one side. This lip provides a little snap-action detent when inserting or removing a patch cable, and probably also prevents the semipermanent components from rotating. You might also notice why those binding posts are "semipermanent": each one is held in place with a little snap ring.

In a sense what we've found looks like the military-grade version of the common electronic breadboard. But some of the big questions still remain. What kind of instrument or machine did this come out of? What did this board actually plug into? Was its "backplane" the interface to a complex system, or just a simple block that connected together the four pins in each checker-square together? And, why so rugged?

Armed with the manufacturer name and the new certainty that this is some kind of patch panel, we did some more searching and turned up what appears to be an actual usage example of one of these panels, at the scale of our original artifact:

This patchboard cartridge-- this one consisting of two of these AMP panels together in a frame with a handle --is one of ten created for a set of art and engineering performances in the mid 1960's. The engineers devised a way to quickly reconfigure stage wiring between different acts going on stage, all of whom needed different wiring.

For each act, they configured the stage wiring appropriately the patchboard: Mike 1 goes to Effects Processor 3 to Amp 2 and so forth. Once the wiring for a given act was complete, all that they had to do was remove the front panel-- as a cartridge -- and set it aside for later use. Because the custom wiring is attached to the removable cartridge, it's easy to quickly switch between customized setups. And with the rugged design, it will survive repeated insertion and removal without dislodging the patch wires or any semipermanent electronics installed on board.

(Photo: Éric Legendre. From The Daniel Langlois Foundation for Art, Science, and Technology, 9 Evenings: Theatre and Engineering fonds.
http://www.fondation-langlois.org/html/e/page.php?NumPage=294)

Now, to revisit our original mystery object.

This one was made of modern injection molded plastic. These things often show their age, and those didn't appear to date back even as far back as 1981. The design is in the style of those older patch panels, and it is very likely that it was used in the same way-- as an interchangeable faceplate for a patch bay of some sort.

There are some differences, however. For one thing, the holes sizes and spacing don't appear to be an exact match with the Amp panels. Perhaps more importantly, the holes are circular all the way through, without any D-shaped retaining lip. The retaining lips are necessary in the Amp boards, because there is significant insertion force when the patchboard cartridge was plugged in and all those pins (including the movable patch cables) need to make contact with the corresponding pins in the backplane-- and not pop out in the process. But these don't have that feature-- so it's reasonable to suppose that the insertion force from swapping cartridges was much lower.

So what does it all add up to? Here is our conclusion: This a fiber optic patch panel, part of an interchangeable faceplate system, that allows the operator to quickly switch between different fiber optic "wiring" configurations. The faceplate brings the fibers up to the backplane, which they butt up against, rather than insert into. An old solution to the modern version of an old problem.

So once again, we'll open it up for questions as well: Have you ever come across any of these? Got one to show us, or a different conclusion? We'd love to hear about it in the comments.