Slightly rare Mac 512k with D(?)-25 connector

Ethan Dicks ethan.dicks at gmail.com
Wed Sep 5 10:49:50 CDT 2007


On 9/5/07, Mark Tapley <mtapley at swri.edu> wrote:
> All,
>         spotted in the San Antonio Goodwill Computerworks:
>
>         A Mac 512k, but with a minor difference. On the back side,
> above where the power switch normally is and far away from the rest
> of the connectors, is a 25-pin D connector reminscent of the Mac
> "SCSI" connectors on Mac Plus and other machines. I did not
> disassemble or power up the machine (no KB or Mouse in evidence), so
> I don't know what it is.

Could be SCSI.

I have one myself - it was one of the 512K Macs my mother used in the
mid 1980s for her typing and typesetting shop.  I upgraded that one to
a 512Ke (double-sided floppies and replacement ROMs), then installed a
"Dove Snap" 512K and SCSI expansion.  You removed the 512K mobo, then
positioned the Dove Snap over the right part of the mobo, then pressed
down with a *large* amount of force to "snap" the expansion board
connectors right over the legs of chips on the mobo.  Think of a bunch
of 5mm-tall Gompers Clips and you aren't too far off.  I don't recall
what pins were tapped, but it was certainly all the necessary signals
from the memory field to refresh another 512K.  There must have been
some unused memory select on a 74LS138 or something to enable the new
memory, and probably the 5380 SCSI chip.  The connector for this one
was on the back of the battery door - you removed the factory battery
door, threaded a 24-pin cable through the back of the battery
compartment, then plugged it into the Dove Snap before reassembling
the case.

In effect, the Dove Snap turned her 512Ke into a Mac Plus, with DE9
serial/printer connectors.  She was using Farallon PhoneNet, with a
networked Apple LaserWriter, so the lack of DIN serial/network didn't
matter.

This was all in the 1985-1989 timeframe - I was happy to be her
in-house Mac hardware dude, especially since it meant that I had a key
and could work on papers after hours with, in effect, a personal laser
printer.  If you think back to those days, that was a nice perk.  (We
also used to go over and play NetTrek on her collection of 512Kes and
Pluses and SEs, but the laser printer was what really did it for me).

>         Don't know whether they'll pak/n/ship. They were asking $5
> for the machine.

If you don't already have a 512K machine, that certainly sounds cheap.
 Keyboards and mice shouldn't be hard to find.

>         Forgotten what the correct designation for those D-connectors
> is, and wanted to get this out fast in case anyone wants it.

Mac SCSI is a DB25F - it's one of those times when it _really_ is a DB
connector.

-ethan



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