unibus backplane list?

Dwight K. Elvey dwight.elvey at amd.com
Mon Aug 15 17:33:33 CDT 2005

>From: "Joe R." <rigdonj at cfl.rr.com>
>At 02:31 PM 8/15/05 -0700, Dwight wrote:
>>>From: "Joe R." <rigdonj at cfl.rr.com>
>>>At 03:51 PM 8/12/05 -0600, you wrote:
>>>>On 8/12/05, Brad Parker <brad at heeltoe.com> wrote:
>>>>> Is there a list of the various pdp-11 unibus backplanes anywhere?
>>>>I do not know of a master list online.
>>>>> My 11/44 has a DD11-DF in it which is impossible to get cards into and
>>>>> out of.  It's like something is physcally wrong with it.  Rather than
>>>>> damage any cards I thought I'd replace it.
>>>>It takes a bit of force to get hex cards in a nearly-unused backplane.
>>>> I've bent latches trying to get boards in. 
>>>   I've had similar trouble with the HP 1000 boards. I found that if I
>>>clean the edge connectors and them wipe them with a rag slightly dampened
>>>with WD-40 (mostly kerosene, a light oil) that the cards go in and out much
>>>easier and I have a lot less intermitant contacts. I believe the oil
>>>coating also helps reduce oxidation of the contacts.
>>>  Joe
>> From what I've been told, WD-40 contains both silicon and
>>petrolium oils. I prefer using silicon grease for this purpose.
>>Past experiments with petrolium oil and grease showed that the
>>contact resistance increased on clean contacts while the
>>silicon grease showed a significant drop in resistance.
>> I recommend Dow-Cornings, DC-4.
>   Does DC-4 lower the force required to insert and remove the board? Where
>can you get it? Any idea how much WD-40 increases the contact resistance?
>Even if it does increase the resistance it has cured many of problems that
>I've had with the 1000s so it seems to do more good than harm.
>   Joe

Hi Joe
 Most any electrical supply shop has it or can get it.
McMaster-Carr list it as well.
 The measurements were done with petrolium grease but
I forget which one. We'd see a normal 10 milli-ohm contact
go as high as 20-30 milli-ohms. The silicon grease would
usually take a 10 milli-ohm dry contact and reduce it to around
2.5 milli-ohms ( close to our measurement limit, using a
4 point DVM ). These were typical gold-gold edge connectors.
 It does reduce the force required but not as much as the
petrolium grease did. I'd suspect that it might be similar
to the wd40, being a lighter oil.

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