[time-nuts] HP E1938

Richard (Rick) Karlquist richard at karlquist.com
Sat Apr 15 19:01:16 EDT 2017

It's been 20 years, but I will try to recap what I remember
about this connector.  I believe there were 3 customers,
and one of them required the DB connector with coax inserts
for reasons of backward compatibility.  I think this
vendor was Motorola.  We did not actually use the coax
inserts, but left them blank and ran the RF, etc on
ordinary pins.  I believe you can make an ordinary male
DB-25 mate with these insert versions by clipping off some
of the pins that would be blocked by the female insert
version.  I vaguely remember that the other 2 vendors
used gender changers or something.  There might have
an issue with the mating plane location being different
for different customers.

I am sure that time-nuts, being talented at repurposing,
will be able to think about this problem and come up with
a simple solution to interfacing with these boards.
No need to buy insert type connectors.  I never had
any trouble making cables that connected to these units
using plain vanilla DB25's.

Rick N6RK

On 4/15/2017 10:42 AM, Larry McDavid wrote:
> Ok, so a standard DB 25-pin socket-contact connector will mate with the
> on-board connector with the center hole and missing pins. That's good!
> I now notice a comment on your webpages about this device in which you
> mention a schematic. Do you have a schematic of this board? If so, can
> you point to it or send me a copy.
> I was unaware of the complete packaged unit on eBay; thanks for that.
> Another poster mentioned the wiring of the connector on the full
> instrument version power connector; is that pin-out and spec available?
> Larry
> On 4/15/2017 5:05 AM, Tom Van Baak wrote:
>>> I purchased one of these HP E1938 OCXO recently on eBay but have not yet
>>> received it.
>>> Is that special D-Submin connector a receptacle-shell, pin contact
>>> version? Will a standard plug-shell, socket contact 25-pin D-Submin
>>> fit it?
>> Hi,
>> I'll cc the group here since we may get some useful comments.
>> I'm not exactly sure what you mean. The E1938A oscillators that I've
>> seen and tested look like this:
>> http://www.leapsecond.com/museum/e1938a/
>> And those can be interfaced with a simple D-sub DB25 connector on the
>> PCB. For connections, see that page, or any number of postings about
>> the E1938 in the time-nuts archives.
>> Note that on eBay there are at least three variations of E1938A
>> oscillator. The item#'s below are just random search picks (I have no
>> affiliation with any buyers or sellers) and I also know not all
>> surplus refurbished surplus recycled surplus stuff works. But we do
>> this because when they did work, they are sometimes totally amazing.
>> 1) There's the bare "puck" alone, as in
>> http://www.ebay.com/itm/290829077542 -- and I have no idea where one
>> would start with that item since all the support circuitry on the PCB
>> would have to be re-created by hand.
>> 2) There's the integrated PCB assembly, as in
>> http://www.ebay.com/itm/181043193416 -- which is more like what I tested.
>> 3) There's the full instrument version, as in
>> http://www.ebay.com/itm/171293069062 -- which is most likely to work,
>> or be less hacked up, or dented, or salvaged, or rusted. It even has
>> all the connectors and power supplies, and GPS, etc.
>> If any other time nuts have experience with each of these methods to
>> obtain a E1938 oscillator, please let us know.

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