UNIBUS backplane finger contact repair

Adrian Stoness tdk.knight at gmail.com
Sat May 16 11:57:18 CDT 2015

the fingers are cast in place or least they are on the 8i backplane
i know this cause i have a bucket of smashed up bits from the 8i i found..

On Sat, May 16, 2015 at 6:48 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>

>     >> it looks like the backplane blocks .. are cast around them
>     > From: Brent Hilpert
>     > all have secured the pin in the housing via some deformation of the
> metal
>     > pin, post-insertion; as opposed to moulding the housing around the
> pin.
>     > From: Ethan Dicks
>     > these are cast blocks of plastic with embedded pins.
>     > From: Jon Elson
>     > On some of the connectors, the pins are pressed in from the card
> side.
> There appears to be some question as to whether thyy are cast in place,
> or inserted.
> Actually, I started to wonder about my assertion shortly after I posted it,
> and took another look at the backplane. The thing is that the hollows that
> the finger contact pins are in are fairly complicated (since they allow the
> contact pins to move back and forth, but hold them from going too far), and
> I'm really wondering if it would be possible to cast that shape, and then
> remove the mold, and also have the pin in there. So I'm wondering if in
> fact
> they weren't inserted post-casting.
>     > From: Brent Hilpert
>     > The problem in your situation of course, is getting the remainder of
>     > the pin out from between the edge connector housing and the backplane
>     > PCB without having to unsolder the entire connector.
> Well, I'm kind of assuming they are inserted from the edge-connector side,
> and not the wira-wrap pin side (what with the contact pins being bent, etc
> on
> the edge-connector side), If they _were_ inserted from the wire-wrap pin
> side, I'm totally @&@^$#%@&^, there's no way to get that PCB off now.
> So in theory, at least, I'd have to de-solder them from the PCB and then
> try
> and push the remaining part back through (after identifying and defeating
> whatever the capture mechanism is - which I might not be able to reach with
> the PCB in the way). And then I'd have to find replacement pins and put
> them
> in. Both of those sound non-trivial.
> (All assuming, of course, that they are inserted post-casting, and not
> cast into place... still not sure about that.)
> This has assumed a little extra urgency as on closer examination, some of
> the
> pins in the UNIBUS in-out area are clearly very weak - I imagine there's
> only
> a tiny bit of metal holding the contact pin in place, and it could break
> off
> any time. And I won't be so lucky as to have them all be ground pins..
> So if one breaks off, the backplane is toast (unless it's the the last
> thing
> on the UNIBUS, it could be kludged - i.e. attach the termination/ pull-up
> directly to the wire-wrap pin).
> Which I guess is not the end of the world - DD11's aren't _that_ rare...
>         Noel

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